Fig. 1.1
Small RCC discovered incidentally on CT. (a) Contrast-enhanced CT shows a 2.4 cm-sized, hypervascular mass (arrow) in the left kidney. (b) The diameter of the mass increased as much as 2 mm during 2-year follow-up without metastasis. Clear cell RCC was confirmed after partial nephrectomy
1.3 Characterization
1.3.1 US
Renal masses can be divided into solid and cystic lesions. Although it is well known that US is accurate in differentiating between cystic and solid renal masses, it is also known that often this differentiation is difficult. Sometimes a homogeneous solid renal mass may be difficult to differentiate from a simple renal cyst if it accompanies posterior sonic enhancement and edge shadowing. The diagnosis of a simple renal cyst can be made if a renal mass is round, well demarcated, and anechoic and accompanies posterior acoustic enhancement. If a renal mass does not meet these criteria but also does not appear as an overt RCC, it can be defined as an indeterminate renal mass and should be evaluated further. Indeterminate renal masses can be categorized into mainly cystic, mixed cystic and solid, and mainly solid renal masses, and the amount of solid portions is important in the suspicion of malignancy [1, 2].
Although the main role of US in renal masses is detection and CT or MRI is usually used for further characterization, US may be required to provide additional information of renal masses detected on CT or MRI. Technical advances in US including tissue harmonic imaging, Doppler US, and contrast-enhanced US (CEUS) increase the ability of US in characterizing renal masses (Fig. 1.2).
Fig. 1.2
Clear cell RCC. (a) Contrast-enhanced CT in corticomedullary phase shows a hypervascular mass (arrow) in the right kidney. The degree of the enhancement is similar to that of the renal cortex. (b) In nephrographic phase, the mass enhances less than the renal parenchyma. (c) Contrast-enhanced US shows early enhancement of the mass (arrows), similar to the renal cortex (*)
1.3.1.1 Solid Renal Mass
The most common solid renal tumor is RCC. Solid renal mass on US in adult should be considered as RCC unless strong evidence of other tumors is present. Differential diagnosis includes AML, oncocytoma, adenoma, lymphomas, metastases, and various benign mesenchymal tumors and sarcomas. A study showed that oncocytomas and AMLs were almost all of benign masses (12.8 %) among 2770 solid renal masses that were surgically removed [3]. AML can show typical US findings such as bright high echo comparable to renal sinus fat (Fig. 1.3). Small RCCs are also usually hyperechoic but may show characteristic findings such as intratumoral cysts and hypoechoic rim (Fig. 1.4). Lymphomas and metastases may be differentiated by clinical settings, but other tumors usually show nonspecific US finding, and other imaging modalities such as CT or MRI are required for further characterization.
Fig. 1.3
AML. (a) Contrast-enhanced CT shows a small, poorly enhancing mass (arrow) in the right kidney. (b) Noncontrast CT shows subtle low attenuation in the mass (arrow). (c) The mass (arrow) shows low SI on T2-weighted MR image. (d, e) Small area of signal drop (arrow) is detected in the mass on out-of-phase T1-weighted MR image (d) compared with in-phase image (e). (f) The mass appears as a brightly high-echoic mass (arrow) on US
Fig. 1.4
US of small RCC. (a) About 2 cm-sized, high-echoic mass shows low-echoic rim (arrow). (b) Small cysts (arrows) are visible in the mass on another plane. (c) Increased vascularity is noted around the mass (arrows) on color Doppler US
1.3.1.2 Cystic Renal Mass
Simple cyst is the most common renal mass detected incidentally. If a cystic mass does not show typical findings of a simple cyst on US, it should be considered a complicated cyst. In evaluating cystic masses based on US findings, internal echoes, septa, wall thickness, calcification, and mural nodularity are important in assessing the risk of malignancy.
Bosniak proposed a four-category classification system of cystic renal masses. Although it is based on CT findings, this classification is widely used also in US or MRI [4].
Bosniak I: Clearly simple cysts that have hairline-thin wall without septa, calcifications, or solid components. Hounsfield units (HU) of CT in the content is usually smaller than 20 (0–20), and does not enhance.
Bosniak II: Minimally complicated cysts with few, thin septa, or thin, fine calcification. The septa may be minimally thickened (Fig. 1.5).
Fig. 1.5
Bosniak II cyst. Thin septal calcification (arrow) is noted on contrast-enhanced CT
Bosniak III: More complicated cystic masses that contain thick or irregular walls or septa in which enhancement can be measured (Fig. 1.6).
Fig. 1.6
Bosniak III cyst. Irregular wall and nodular thickening of a septum (arrow) is visible on contrast-enhanced CT. This cyst turned out to be cystic nephroma after surgery
Bosniak IV: Clearly malignant cystic masses that not only contain all the characteristics of Bosniak III lesions but also contain enhancing soft tissue components adjacent to, but independently of, the wall of septa. Most malignant complex renal cysts are cystic renal cell carcinomas (Fig. 1.7).
Fig. 1.7
Bosniak IV cyst. A complex cystic lesion in the left kidney shows multiple irregular septa with enhancement on contrast-enhanced CT. Multilocular cystic RCC was the pathologic diagnosis
In Bosniak classification, the probability of malignancy is virtually 0 % for I and almost 100 % for IV. The problem in this classification is almost always the differentiation between II and III, because the criteria are apt to be subjective. In 1993, Bosniak added class IIF, which is a little bit more complicated than class II, but less than class III, and so needs close follow-up (Fig. 1.8).
Fig. 1.8
Bosniak IIF cyst. (a). Noncontrast CT shows a hyperattenuating nodule (arrow) in the left kidney. (b). This nodule shows no definite enhancement on contrast-enhanced CT, suggesting hemorrhagic cyst
Malignant risk of Bosniak IIF and III lesions is known as 5–10 % and 40–60 %, respectively [5]. A recent study retrospectively evaluated the outcome of Bosniak IIF and III cysts and reported higher malignancy rate (25 %) in IIF lesions and similar rate (54 %) in III lesions. However, in this study, resected Bosniak IIF lesions were highly selected in patients with a high number of risk factors associated with malignancy: a history of primary renal malignancy, coexisting Bosniak IV lesion, and/or solid renal neoplasm [6].
1.3.1.3 Doppler US and Contrast-Enhanced US
Color Doppler US (CDUS) or power Doppler US (PDUS) can be helpful in evaluating indeterminate renal masses by depicting vascularity in the mass (Fig. 1.4). Increased vascularity in a renal mass can suggest malignancy, whereas the absence of flow signals may suggest high likelihood of benign lesion. However, the presence of flow signals in the septa of a cystic mass does not always indicate malignancy, because benign neoplasms such as cystic nephroma or even nonneoplastic cysts may show flow signals in the septa. Flow signals on CDUS or PDUS should be confirmed by using spectral Doppler US, because artifacts may mimic flow signals.
Contrast-enhanced Doppler US can increase the detection of intratumoral vascularity compared to CDUS and PDUS. Recent development of contrast-enhanced harmonic US imaging has provided for a better assessment of the vascular morphology and the enhancing patterns of renal tumors, such as early enhancement and washout of RCC, in contrast to delayed and prolonged enhancement of AML (Fig. 1.2). Ultrasound contrast agents are strictly intravascular and not excreted by or retained in kidneys, so that they can be used in patients with renal failure or urinary obstruction, unlike CT or MRI. Because CEUS is very sensitive for vascularity, it is especially useful in the differential diagnosis of hypovascular renal tumors or the detection of blood flow in the septa of complex renal cysts, even if enhancement on CT is equivocal [7]. A study showed higher sensitivity of CEUS in the diagnosis of hypovascular renal tumors compared with contrast CT (94.4 % vs 88.9 %) [8]. In a prospective study comparing CEUS with CT in the assessment of complex renal cysts, CEUS was proved to be appropriate for renal cyst classification with the Bosniak system, and complete concordance between CT and CEUS was observed regarding the need for surgery [9]. Another study demonstrated the superiority of CEUS as compared to grayscale US and to CT for the diagnosis of complex renal cysts [10].
1.3.2 CT
1.3.2.1 Unenhanced CT
Renal cysts show low attenuation (0–20 HU) on CT images regardless of contrast enhancement, but hemorrhagic cysts may show higher attenuation on unenhanced CT. These high-attenuation cysts should be categorized as Bosniak IIF, and follow-up is required (Fig. 1.8). Complicated cysts may show septal or wall calcifications, and close comparison with contrast-enhanced images should be made to differentiate from enhancing part. Solid RCCs usually show attenuation similar to surrounding renal parenchyma. However, the attenuation becomes heterogeneous in large tumors due to hemorrhage or necrosis. Calcifications in a renal mass may suggest malignancy, because RCCs can contain calcifications but AMLs do not. AMLs usually show higher attenuation than RCCs on unenhanced CT and contain low-attenuation part comparable to fat (Fig. 1.9). However, 5 % of AMLs do not contain enough fat to be detected on CT (Fig. 1.10). In these fat-free or fat-deficient AMLs, the analysis of the shape and the enhancement pattern of the mass may be clues for the differentiation.
Fig. 1.9
AML. (a) Noncontrast CT shows fatty component (arrow) of a mass in the right kidney. (b, c) Nonfatty component of the mass (arrow) enhances well in corticomedullary phase (b) and shows persistent enhancement in nephrographic phase (c)
Fig. 1.10
Multiple AMLs in tuberous sclerosis. (a) Noncontrast CT shows a hyperattenuating mass (arrow) without detectable fatty component in the left kidney. (b) This mass (arrow) shows heterogeneous enhancement on contrast-enhanced CT. (c) Other AMLs (arrows) are also found in bilateral kidneys. Note fatty component of an AML (small arrow) in the right kidney
A recent study with 193 pathologically proven RCCs reported that all RCCs contained substantial noncalcified regions that measured 20–70 HU in ROI attenuation on unenhanced CT. Therefore, indeterminate renal lesions on unenhanced CT measuring within this range warrant further workup, whereas lesions that fall entirely outside this range may be considered benign [11].
1.3.2.2 Contrast Enhancement
Renal masses that do not enhance after the injection of contrast material are almost always benign, such as Bosniak I and II cysts. Enhancement in the septa and the wall of a cyst raises the probability of malignancy, and the enhancing solid part strongly suggests the malignancy. However, in small renal masses, enhancement itself is not definite evidence of malignancy because several investigators have reported that about 20 % of the enhancing renal masses smaller than 4 cm turned out to be benign tumors after surgery [12]. On the other hand, severely necrotic masses may fail to demonstrate contrast enhancement in rare instances. Hemorrhage in the mass may mask subtle or small enhancing part, and close comparison with unenhanced CT or follow-up is required. In mildly enhancing lesions, true enhancement should be differentiated from pseudoenhancement due to strongly enhancing renal parenchyma. Although there is no strict cutoff value, a threshold of 20 HU is commonly used to indicate definitive enhancement and values of less than 10 HU as indicating no enhancement [13].
Dynamic contrast enhancement is essential for the differential diagnosis of solid renal masses. RCCs usually show strong enhancement on early or corticomedullary phase, and lower attenuation than renal parenchyma on delayed or nephrographic/excretory phase (Fig. 1.2). This is true in most clear cell-type RCCs, but may be not in other types, such as papillary or chromophobe type. AMLs show variable degree of enhancement according to the ratio of components in the mass. Strong and early enhancement may be visible in AMLs with dominant angiomatous component, and the differentiation from RCC may be difficult. However, most AMLs show less and delayed enhancement compared with clear cell-type RCCs [14, 15].
1.3.3 MRI
MRI can be useful in some circumstances to further evaluate a renal mass. It is usually used as a problem-solving modality in suspicious or undetermined renal masses. MRI can replace CT if patients cannot receive iodinated contrast agent. Furthermore, if the lesion has features such as endophytic property, small size (<1 cm), equivocal enhancement, or confluent areas of dense calcification, MRI may give more sensitive or specific information than CT.
1.3.3.1 Signal Intensity
Cyst or cystic masses show low signal intensity (SI) on T1-weighted image (T1WI) and high SI on T2-weighted image (T2WI), identical to water. Hemorrhagic cysts show various signal, and recent hemorrhage tends to show high SI on T1WI and low SI on T2WI. The septa and wall of complicated cysts usually show low SI on T2WI. Most solid renal lesions appear isointense to the surrounding normal renal parenchyma on T1WI and variable in SI on T2WI. Therefore, SI itself cannot provide many clues to the diagnosis. Chemical shift imaging is helpful to detect small amount of fat in AMLs, which may show signal drop on out-of-phase images (Fig. 1.3). However, this should be interpreted with caution because a similar signal drop can be visible in clear cell RCC due to intracytoplasmic lipid [16]. Renal mass signal on T2WI may be helpful in differentiating fat-deficient AML from clear cell RCC. Fat-deficient AML shows low SI due to its smooth muscle content, whereas clear cell RCC usually shows iso- or high SI on T2WI. Papillary RCC, however, also shows low SI on T2WI. Therefore, T2WI cannot be used to differentiate papillary RCC from AML (Figs. 1.3 and 1.11).
Fig. 1.11
Clear cell RCC in the left kidney and papillary RCC in the right kidney in the same patient. T2-weighted MR image shows bilateral renal masses (arrows). The right renal mass shows low SI but the left mass appears as a heterogeneous mass with high SI
1.3.3.2 Contrast Enhancement
Gadolinium-enhanced dynamic images can increase the diagnostic accuracy of renal masses. However, in MRI, there is no widely accepted method in determining enhancement objectively in renal masses. Subjective comparison of unenhanced and contrast-enhanced images is usually used and may be useful in hypervascular tumors, but the detection of enhancement may be difficult in hypovascular tumors. Hyperintense masses on unenhanced T1WI, such as hemorrhagic masses, are another problem in evaluating enhancement.. In such cases, subtraction technique can be helpful to detect enhancement (Fig. 1.12), and calculation of percent enhancement using arbitrary SI units can be also applied [17, 18].
Fig. 1.12
Xp11.2 translocation–TFE3 gene fusion carcinoma. (a) Noncontrast CT shows a heterogeneous, highly attenuating mass (arrow) in the left kidney, suggesting hemorrhage inside. (b) The enhancement in the mass is difficult to assess due to hemorrhage. (c, d) The mass (arrow) shows high SI on T1WI of MRI (c) and heterogeneous SI on T2WI (d). (e). Subtraction image obtained from dynamic contrast-enhanced MRI shows mildly enhancing component (arrow) in the mass
1.3.3.3 Diffusion-Weighted Imaging (DWI)
DWI is a functional MR imaging based on the diffusion of water molecules in biological tissues. Apparent diffusion coefficient (ADC) can be calculated and mapped on imaging, which reflects the random thermal motion of protons. DWI in renal masses can be useful in identifying solid renal masses and evaluating the possibility of malignancy (Fig. 1.13). Previous studies suggested that DWI could provide comparable accuracy to contrast-enhanced MRI in identifying renal lesions, and combined DWI and contrast-enhanced MRI had more specificity when compared to using those two methods alone [19]. ADC values of malignant solid masses are known to be lower than those of benign masses. Furthermore, the mean ADC value of clear cell RCC was reported to be significantly higher than other subtypes [20]. In a recent study with 3.0Tesla DWI MRI, the mean ADC value was significantly lower in RCC than in normal renal parenchyma, and the ADC value was also statistically different between clear cell RCC and other subtypes of RCCs [21]. However, objective evaluation of DWI is not easy because there is substantial inter- and intra-scanner variability in ADC measurement. ADC values also depend on selected b values that vary across institutions and protocols.
Fig. 1.13
Diffusion-weighted MR imaging of RCC. (a) Contrast-enhanced T1WI of MR shows a round, mildly enhancing mass (arrow). (b) The mass shows low SI on T2WI. Note low-SI rim (arrow) in the periphery of the mass. (c) The mass (arrow) shows decreased diffusion on ADC image
1.3.4 Positron Emission Tomography
FDG PET is capable of visualizing malignant tumors and associated lymph nodes and distal metastatic sites in a single test. In renal cell carcinoma, FDG PET can detect the renal cell carcinoma with various uptake patterns according to the histologic grades. Despite higher specificity, the sensitivity for the detection of malignant renal tumors is quite low of 47–60 % because of the urinary excretion of FDG and incapability of discrimination of tumor uptake and excreted urine activity [22] (Fig. 1.14). However, FDG PET can detect the regional node or distant metastasis for the staging. About 30 % of patients with renal cell carcinoma have metastatic diseases at the initial diagnosis [23] (Fig. 1.15). The lung, bone, and brain are the most common sites of distant metastasis. The sensitivity for detecting metastases is higher than the detection of primary tumors in renal cell carcinoma [24] (Fig. 1.16). Moreover, FDG PET has better diagnostic performance in restaging and recurrence. Nakatani et al. [25] studied the value of FDG PET to detect recurrence disease in 23 postsurgical RCC patients with the sensitivity, specificity, and diagnostic accuracy of FDG PET for detecting recurrent malignancy of 81 %, 71 %, and 79 %, respectively. The higher detection rate of recurrence in renal cell carcinoma enables FDG PET with positive findings as a prognostic marker in patients with recurrent renal cell carcinoma [26]. FDG PET seems to be useful in characterizing anatomic lesions of unknown significance in patients with renal cell carcinoma [27] (Fig. 1.17). However, we need the clinical results in larger-scale patient numbers to establish the clinical utility of FDG PET in staging and restaging renal cell carcinoma.
Fig. 1.14
A 63-year-old man presented with incidentally detected mass in the right kidney. FDG PET shows mild hypermetabolism (3.2 of SUVmax) in the corresponding mass (arrow) on enhanced CT scan. The hypermetabolic mass lesion is discriminated from the adjacent urine activity with an aid of CT localization. Renal cell carcinoma is confirmed on histopathology after radical nephrectomy
Fig. 1.15
A 60-year-old man underwent FDG PET for staging of renal cell carcinoma. Para-aortic lymph node as well as left renal mass shows hypermetabolism (arrows), which were confirmed as renal cell carcinoma with node metastasis after radial nephrectomy
Fig. 1.16
A 57-year-old man presented with incidentally detected renal mass. FDG PET shows an exophytic hypermetabolic mass in the inferior pole of the left kidney with hypermetabolic bone lesion in the sacrum (arrows). FDG PET is a useful method to detect unexpected metastasis in a single test
Fig. 1.17
A 58-year-old man underwent diagnostic work-up for the evaluation of incidentally detected lymph node enlargement in the left aortic lymph node, which was metastatic adenocarcinoma on biopsy. FDG PET shows hypermetabolism in the solid area of the cystic mass which is corresponding with cystic mass in the left kidney on contrast-enhance CT. Clear cell RCC was confirmed on histopathology after resection
Recently, targeted drugs have been developed and approved for use in metastatic renal cell carcinoma. Multikinase inhibitors inhibit the receptor tyrosine kinase VEGF receptor or the platelet-derived growth factor receptor in the endothelial cells and pericytes, respectively [28]. These drugs can be administered in patients with metastatic renal cell carcinoma as single agent, which makes PET imaging with a specific radiotracer that visualizes steps in the metabolic pathway of the targeted drug an attractive biomarker for predicting and monitoring the effect of the drug [29]. The expression of glucose transporter (GLUT) is a downstream product of HIF transcriptional activity. Thus, the intensity of FDG uptake on PET may be reflective of the entire pathway of hypoxia [25]. FDG PET with its variable intensity in renal cell carcinoma may reflect the variable expression of the HIF signaling pathways in tumor hypoxia and expression of its downstream products, which may be predictive marker of the effect of the inhibitors of this pathway [30, 31]. Kayani et al. reported that tumors of renal cell carcinoma with a lower pretherapy uptake on FDG PET demonstrate a larger size decrease on CT after treatment with tyrosine kinase inhibitors [29, 31]. They proposed that the reduction of metabolic activity of more than 20 % in SUV on FDG PET can be used as a predictive marker for targeted therapeutics.
Other kinds of molecular imaging targets have been proposed in order for more specific to renal cell carcinoma. The PET with 11C-acetate can also detect renal cell cancer. 11C-acetate, as a metabolic substrate of beta-oxidation, that is, precursors of amino acid, fatty acid, and sterol, has been proved useful in detecting various malignancies [32]. In addition, it is an advantage for the 11C-acetate that the urinary excretion is negligible compared with FDG on PET imaging. Liu et al. [33] proposed another radiotracer of FLT on PET to characterize and quantify changes in tumor proliferation during sunitinib exposure and its temporary withdrawal and to explore pharmacodynamics changes that may yield insight into predicting treatment response. In another view point of metabolic alteration by hypoxia, tumor hypoxia can be evaluated by 18F-FMISO (Fig. 1.18). However, Hugonne et al. [34] reported that hypoxia in metastatic RCC as assessed by FMISO PET was less frequent and less pronounced than initially suspected.
Fig. 1.18
Tumor hypoxia can be evaluated by 18F-FMISO PET. Two patients with liver metastasis underwent palliative chemotherapy. (a) One patient with a metastatic lesion of high FMISO uptake shows progression and (b) the other patient with a metastasis of low FMISO uptake shows response after palliative chemotherapy (arrow)
In summary, FDG is the most commonly used PET radiopharmaceutical in assessing malignant tumors. However, urinary tract tumor assessment is hampered by the renal elimination of FDG. On the contrary, PET scan using C-11 labeled acetate or other molecular tracers enables us to obtain pelvic images with molecular target specific information in order for staging, restaging, prognosis assessment, response evaluation, and/or prediction as well as without radioactivity of eliminated tracers in the urinary tract [32]. Larger studies are required before it can be advocated for clinical use in the field of urology.
1.3.5 Biopsy
Percutaneous biopsy of renal masses has been usually performed in the suspicion of metastatic renal tumor, for the pathologic diagnosis of unresectable renal mass including multiple, bilateral masses, or suspicion of renal involvement of inflammatory or autoimmune diseases. However, biopsy is also frequently performed in other renal masses nowadays, because nephron-saving surgery becomes popular. Core biopsy can provide an accurate and safe diagnostic tool in small renal masses, which turn out to be benign in 13–16 % after surgery. In a study of 268 small renal masses (≤4 cm) biopsied, diagnostic yield was obtained in 80 % and 26 % of them were benign. The accuracy of biopsy in determining benign or malignant lesions was 100 % in cases where nephrectomy was done [35]. Therefore, biopsy should be offered before surgical intervention in indeterminate small renal masses. US is usually used for guiding biopsy, and CT-guided biopsy is being also used for small masses.
1.4 Malignant Renal Cell Tumors: Renal Cell Carcinoma
The most common renal cell tumor is RCC in adults. It is also the most common renal malignant tumor, comprising more than 90 % of them. Owing to early detection, the incidence of RCC is rising, as 30–40 % of RCCs are detected incidentally by imaging. It is more common in males than females and the most common in 40–60-year-old patients.
In the WHO classification proposed in 2004, several distinct histologic subtypes of RCC include clear cell RCC, papillary RCC, chromophobe RCC, hereditary cancer syndromes, multilocular cystic RCC, collecting duct carcinoma, medullary carcinoma, mucinous tubular and spindle cell carcinoma, neuroblastoma-associated RCC, Xp11.2 translocation–TFE3 carcinoma, and unclassified lesions. Sarcomatoid RCC is considered as the result of sarcomatoid dedifferentiation of other RCCs and no longer a subtype [36].
1.4.1 Pathologic Consideration
1.4.1.1 Clear Cell Renal Cell Carcinoma
Grossly, clear cell renal cell carcinoma is relatively well demarcated and frequently uncapsulated but occasionally has fibrous pseudocapsule. On cut surface, clear cell renal cell carcinoma typically reveals golden yellow color, and high-grade area shows white to gray cut surface (Fig. 1.19). They frequently have variable cystic change, hyaline change, necrosis, and hemorrhage (Fig. 1.19c). Calcification or ossification is rarely found.
Fig. 1.19
Macroscopic findings of clear cell renal cell carcinoma. (a) Grossly, clear cell renal cell carcinoma typically shows golden-yellow-colored cut surface. (b) Occasionally whitish- to grayish–colored area (arrow) can be found in high-grade clear cell renal cell carcinoma. (c). Hyaline changes, cystic changes, or hemorrhages are frequently found
Histologically clear cell renal cell carcinoma shows various architectural patterns such as solid sheet, nest, alveolar, tubular, or microcyst formations. Tumor cells typically have clear cytoplasm with distinct cell border (Fig. 1.20a), but eosinophilic granular cytoplasm can be found especially in high-grade area. Rhabdoid feature of tumor cells is rarely found (Fig. 1.20b) [37, 38] and is associated with aggressive behavior and metastasis [39, 40]. Tumor cell nuclei of low-grade clear cell renal cell carcinoma are small, round, and uniform with fine chromatin. High-grade clear cell renal cell carcinomas generally have larger nuclei with prominent nucleoli. Highly pleomorphic nuclei can be found in high-grade tumor. Sarcomatoid change is also found in about 4–5 % of clear cell renal cell carcinomas [41, 42] (Fig. 1.20c).
Fig. 1.20
Microscopic findings of clear cell renal cell carcinoma. (a) Tumor cells of clear cell renal cell carcinoma typically have clear cytoplasm and distinct cell border. (b) Some tumor cells of this clear cell renal cell carcinoma reveal rhabdoid changes (arrow). (c) Sarcomatoid change of clear cell renal cell carcinoma shows malignant spindle cells between clear tumor cell nests
1.4.1.2 Multilocular Cystic Renal Cell Carcinoma (Multilocular Cystic Neoplasm of Low Malignant Potential)
Multilocular cystic renal cell carcinoma is a well-demarcated multicystic mass without solid or expansile tumor nodules. Generally, this tumor is entirely cystic with fibrous capsule, thin septa, and multiple cysts containing clear or bloody fluid (Fig. 1.21).
Fig. 1.21
Multilocular cystic renal cell carcinoma shows well-circumscribed multiple cysts without solid tumor nodules
Microscopically, multilocular cystic renal cell carcinoma is composed of multiple cysts lined by mainly single layer of clear tumor cells, but lining cells are often absent. Small clear cell clusters can be present in fibrous septa. Tumor cells have small low-grade nuclei with clear cytoplasm (Fig. 1.22).
Fig. 1.22
Microscopically, cyst wall is lined by tumor cells with clear cytoplasm and low-grade nuclei
1.4.1.3 Papillary RCC
Papillary renal cell carcinoma is a well-demarcated mass with frequent fibrous pseudocapsule. Cut surface of papillary renal cell carcinoma reveals gray to red brown to golden yellow color with frequent hemorrhage and necrosis (Fig. 1.23).
Fig. 1.23
Macroscopic findings of papillary renal cell carcinoma. (a) A papillary renal cell carcinoma shows a well-circumscribed mass with encapsulation. On cut surface, massive hemorrhage and necrosis are found. (b) This papillary renal cell carcinoma reveals prominent yellow color, indicating lipid-laden macrophage collections
Microscopically, the main architectural pattern of papillary renal cell carcinoma is papillary arrangement with fibrovascular core and occasionally shows tubular arrangement. The papillae are covered by single layer of tumor cells or occasionally pseudostratified tumor cells. Varying degrees of aggregates of lipid-laden macrophages are frequently found in fibrovascular core. Psammomatous calcifications are occasionally present. Papillary renal cell carcinoma is classified into two subtypes, type 1 and type 2 [43, 44]. Type 1 papillary renal cell carcinoma shows small tumor cells with scanty basophilic cytoplasm, small nuclei, and inconspicuous nucleoli. Covered tumor cells mainly form single layer (Fig. 1.24a). Type 2 papillary renal cell carcinoma is characterized by tumor cells with voluminous eosinophilic cytoplasm, large nuclei, and prominent nucleoli. Tumor cells are frequently pseudostratified (Fig. 1.24b). Type 2 papillary renal cell carcinomas show more aggressive behavior [43].
Fig. 1.24
Microscopic findings of papillary renal cell carcinoma. (a) Type 1 papillary renal cell carcinoma shows well-formed papillary configurations lined by small tumor cells with scanty cytoplasm and small nuclei. Foamy macrophage collections are found. (b) Type 2 papillary renal cell carcinoma reveals papillary architectures lined by eosinophilic tumor cells with abundant cytoplasm and prominent nucleoli. Tumor cells show pseudostratification. Foam cell collections are also found
1.4.1.4 Chromophobe RCC
Grossly, chromophobe renal cell carcinoma is a well-circumscribed mass with yellow-tan- to brown-colored, homogeneous cut surface (Fig. 1.25). Hemorrhage or necrosis is rarely found. Central fibrous scar can be present.
Fig. 1.25
Grossly, chromophobe renal cell carcinoma is a well-defined mass with yellowish cut surface
Microscopically, tumor cells of chromophobe renal cell carcinoma are mainly arranged in solid sheet or trabecular pattern. Tumor cells have distinctive thick cell border and abundant pale eosinophilic to clear cytoplasm (Fig. 1.26a). Perinuclear halo is frequently found (Fig. 1.26b). Nuclei of chromophobe renal cell carcinoma are small and uniform and occasionally have irregular nuclear membrane. Binucleated nuclei are also present. Sarcomatoid change is rarely found in chromophobe renal cell carcinoma (Fig. 1.26c).
Fig. 1.26
Microscopic findings of chromophobe renal cell carcinoma. (a) Tumor cells are arranged in solid pattern. Cytoplasms are clear or eosinophilic with thick cell border. (b) Perinuclear halo is frequently found. (c) Sarcomatoid change of chromophobe renal cell carcinoma shows malignant spindle cells between typical tumor cell nests
1.4.1.5 Carcinoma of Collecting Duct of Bellini (Collecting Duct Carcinoma)
Collecting duct carcinoma is mainly located in renal medulla and often involves renal cortex. Generally, this tumor shows white- to gray-colored, firm cut surface with infiltrative border (Fig. 1.27). Hemorrhage and necrosis are frequent.
Fig. 1.27
Collecting duct carcinoma is a whitish firm mass with infiltration into the renal parenchyma
Microscopically, collecting duct carcinoma is mainly composed of irregular-shaped tubules and papillae. Tumor cells have high-grade morphology with eosinophilic cytoplasm and pleomorphic nuclei (Fig. 1.28). Frequent mitosis, desmoplastic stroma, and infiltration into surrounding renal parenchyme are typical features of collecting duct carcinoma.
Fig. 1.28
Microscopic findings of collecting duct carcinoma. Tumor shows tubulopapillary architecture with fibrotic stroma. Nucleoli are prominent
1.4.1.6 MiTF/TFE Family Translocation-Associated Carcinoma
This specific renal cell carcinoma subtype is defined by gene translocations between MiTF/TFE family gene (TFE3 (Xp11.2), TFEB (6p21)), and variable partner genes including PRCC (1q21) and ASPL (17q25) [45–50]. TFE3 translocation renal cell carcinomas and TFEB translocation renal cell carcinomas are included in this category.
Grossly, TFE3 translocation renal cell carcinoma has variable gross appearance. Sometimes this tumor has infiltrative border. Cut surface shows white, tan, or yellow color with occasional necrosis and hemorrhage (Fig. 1.29) [46, 47].
Fig. 1.29
This TFE3 translocation renal cell carcinoma is a whitish mass with focal hemorrhage
Microscopic features can be variable according to translocation type. Many reported cases show tubulopapillary architecture with voluminous clear to eosinophilic cytoplasm and often psammomatous calcification in TFE3 traslocation renal cell carcinomas (Fig. 1.30) [46, 47].
Fig. 1.30
Microscopic findings of TFE3 translocation renal cell carcinoma. (a) TFE3 translocation renal cell carcinoma frequently shows papillary configurations. (b) Clear tumor cells and calcifications are found in this tumor
Immunohistochemistry and FISH study help in the correct diagnosis of these translocation carcinomas [51]. Immunohistochemical staining for TFE3 shows strong and diffuse nuclear positivity in TFE3 translocation carcinoma (Fig. 1.31a). TFE3 break-apart FISH study reveals split signals of TFE3 gene (Fig. 1.31b) [52, 53].
Fig. 1.31
Ancillary tests for TFE3 translocation renal cell carcinoma. (a) Immunohistochemical staining for TFE3 shows diffuse strong nuclear staining in TFE3 translocation carcinoma. (b) TFE3 break-apart FISH study shows one set of fused signal and one set of red and green split signals (arrows) in TFE3 translocation renal cell carcinoma
1.4.1.7 Mucinous Tubular and Spindle Cell Carcinoma
Grossly, mucinous tubular and spindle cell carcinoma is a well-demarcated solid homogeneous mass with pale yellow- to gray-colored cut surface (Fig. 1.32).
Fig. 1.32
Gross photograph of mucinous tubular and spindle cell carcinoma shows a well-demarcated solid whitish mass with homogeneous cut surface
Microscopically, mucinous tubular and spindle cell carcinoma is composed of small tightly packed tubules and spindle cells with mucinous stroma (Fig. 1.33). Tumor cells generally have low-grade nuclei and scanty cytoplasm.
Fig. 1.33
Microscopically, this mucinous tubular and spindle cell carcinoma reveals vague tubule formation and spindle-shaped cells with mucinous background. Tumor cells have low-grade nuclei
1.4.1.8 Renal Cell Carcinoma Associated with End-Stage Renal Disease (ESRD)
Two specific renal cell carcinoma types are frequently related to end-stage renal disease [54].
Acquired Cystic Disease-Associated Renal Cell Carcinoma
Acquired cystic disease-associated renal cell carcinoma is generally found in acquired cystic disease patients on dialysis. Grossly, acquired cystic disease-associated renal cell carcinoma is a well-circumscribed small tumor and is often found within cysts (Fig. 1.34a). Microscopically, this tumor shows acinar, alveolar, solid, and cystic pattern. The tumor cells have abundant eosinophilic cytoplasm and prominent nucleoli (Fig. 1.34b) [55].
Fig. 1.34
Pathologic features of acquired cystic disease-associated renal cell carcinoma. (a) Grossly, acquired cystic disease-associated renal cell carcinoma is a well-circumscribed mass with cystic change. (b) Microscopically, tumor cells have abundant eosinophilic cytoplasm
Clear Cell Papillary Renal Cell Carcinoma
Clear cell papillary renal cell carcinoma is found in ESRD or non-ESRD patients. Grossly, this tumor is a well-circumscribed yellowish or whitish mass with fibrous capsule and occasional cystic change (Fig. 1.35a). Microscopically, clear cell papillary renal cell carcinoma is composed of exclusively clear cells with tubule–papillary architecture (Fig. 1.35b). Nuclei are generally low grade. Unlike papillary renal cell carcinoma, foamy macrophages are not present. Cystic change is frequently found [56].
Fig. 1.35
Pathologic features of clear cell papillary renal cell carcinoma. (a) Grossly, clear cell papillary renal cell carcinoma is a well-circumscribed whitish mass with encapsulation and frequent cystic change. (b) Microscopically, clear cell papillary renal cell carcinoma is composed of clear cells with tubule–papillary architecture. Tumor cell nuclei are low grade
1.4.1.9 Unclassified Renal Cell Carcinoma
Unclassified renal cell carcinoma is defined as renal cell carcinomas that cannot fit into one renal cell carcinoma category. Some cases have morphologic features of two or more renal cell carcinoma types. Other cases are high-grade undifferentiated cases or pure sarcomatoid renal cell carcinoma [57].
1.4.1.10 Nuclear Grading of RCC
Fuhrman nuclear grading is a very important prognostic factor of renal cell carcinoma [58]. This grading system is mainly defined by nuclear size and nucleolar prominence. Tumors of Fuhrman grade 1 have small dense nuclei with no visible nucleoli in × 10 objective lens. Grade 2 tumors have fine granular open chromatin with inconspicuous nucleoli. Nucleoli are identifiable at higher magnification (×40 objective lens). Grade 3 tumors reveal prominent nucleoli that can be easily identifiable at × 10 objective lens. Grade 4 nuclei show nuclear pleomorphism with large nucleoli (Fig. 1.36).
Fig. 1.36
Fuhrman nuclear grading of renal cell carcinoma. (a) Fuhrman nuclear grade I. Tumor cells have small nuclei and inconspicuous or invisible nucleoli (×400). (b) Fuhrman nuclear grade II. Tumor cells show distinct nucleoli at high magnification (×400) but not conspicuous at × 10 objective lens. (c) Fuhrman nuclear grade III. Tumor cells reveal distinct nucleoli at this magnification (×100). (d). Fuhrman nuclear grade IV. Tumor cells have large and pleomorphic nuclei
1.4.2 Imaging
1.4.2.1 Staging
The TNM staging system of RCC is summarized in Table 1.1. T1 and T2 tumor without nodal or distant metastasis belongs to Stage I and II, respectively. Stage III means T3 or N1 disease without distant metastasis, and T4 or M1 disease are in stage IV [59]. The staging is important not only in predicting the prognosis but also planning the treatment, because tumorectomy or partial nephrectomy is preferred in locally noninvasive tumors nowadays.
Table 1.1
TNM Staging system of RCC (7th edition)
T1 | Tumor confined to renal capsule |
T1a | ≤4 cm |
T1b | 4–7 cm |
T2 | Tumor confined to kidney |
T2a | 7–10 cm |
T2b | >10 cm |
T3a | Spreading into perinephric tissue, renal sinus, or renal vein |
T3b | Spreading into inferior vena cava (IVC) below diaphragm |
T3c | Spreading into IVC above diaphragm or invasion into wall of IVC at any level |
T4 | Beyond Gerota’s fascia or direct invasion into ipsilateral adrenal gland |
N0 | No nodal involvement |
N1 | Regional lymph node(s) metastasis |
M0 | No distant metastasis |
M1 | Distant metastasis |
In staging of RCC, invasion into renal fascia or adjacent organs, renal vein thrombosis, regional lymph node enlargement, or distant metastasis are important CT findings (Fig. 1.37). Multidetector-row CT (MDCT) is now the imaging modality of choice for staging and preoperative planning of RCCs. MDCT increases the accuracy of CT in staging RCC compared with MRI. In a prospective study to compare the diagnostic accuracy of MRI and MDCT, similar accuracy (0.78–0.87 vs 0.80–0.83) was shown. MDCT also yields similar staging results in evaluating the extent of venous thrombosis as MRI [60].
Fig. 1.37
RCC staging on CT. Contrast-enhanced CT in coronal plane shows a large RCC (large arrow) in the left kidney. Multiple lymph node metastases (white small arrows) and thrombus in the inferior vena cava (black small arrow) are important findings for staging
When considering nephron-sparing surgery, the detection of intrarenal infiltrations of RCC is important. MDCT shows good sensitivity in predicting arterial infiltration but the lowest specificity in excluding infiltration of the renal pelvis [61]. In the detection of perirenal fat invasion, stranding, collateral vessels, fat obliteration, discrete soft tissue mass, and fascial thickening are suggestive CT findings. Among them, mass over than 1 cm is the only strong evidence of perirenal invasion. The interruption of the pseudocapsule, which is formed by compressed renal parenchyma around RCC, is an important sign of locally invasive tumor within perirenal fat. On MRI, the pseudocapsule appears as low SI rim in the periphery of tumor on T2WI (Fig. 1.13). Multiplanar images are required to prove an intact pseudocapsule, which implies a lack of perinephric fat invasion and that the tumor can be removed by partial surgery. The pseudocapsule also appears as low-attenuation rim on contrast-enhanced CT (Fig. 1.38), and a recent study reported that the accuracy of MDCT in the detection of pseudocapsule was 83 % with the histopathologic results as the standard of reference. Imaging in the portal and nephrographic phases with coronal and sagittal reformations proved more accurate in the detection of pseudocapsule [62].
Fig. 1.38
Pseudocapsule of RCC on CT. Contrast-enhanced CT shows a hypervascular mass in the left kidney. Note thin, low-attenuation rim (arrow) between the mass and renal parenchyma
MDCT is also important in providing renal vascular information before surgery. Multiplanar reformation (MPR) and 3D volume-rendering (VR) images can provide the accurate information of the renal vasculature including the number, early branching and late confluence of renal vessels, the relations with the collecting system, and the depiction of anatomic variants. In a series of 47 cases with two-phase MDCT angiography, the accuracy for the only-arterial anatomy was 97.9 % and only-venous anatomy was 100 %. This result can suggest the MDCT angiography can fully replace catheter-based angiography for assessing vascular supply of the kidney before surgery [63].
1.4.2.2 Subtypes of RCC
Because prognosis is significantly different among subtypes of RCCs, preoperative knowledge of the subtype is important in planning treatment. CT may differentiate these subtypes based on the degree of enhancement, enhancement pattern, calcification, and tumor-spreading patterns. 91–100 % specificity was reported in differentiating clear cell RCCs from other subtypes on biphasic contrast-enhanced CT, depending on the degree of enhancement. Homogeneous enhancement is the most common in chromophobe type, and calcification is more common in papillary and chromophobe types. Perinephric change and venous invasion are common in collecting duct carcinoma [64].
Clear Cell RCC
Clear cell RCCs are the most common subtype of RCC (70–75 %). Multicentric (5 %) or bilateral (1–2 %) tumors are rarely encountered. They are usually spherical and the margin is smooth and well demarcated. They are located in the renal cortex with expansile growth. The tumors are often surrounded by the pseudocapsule formed by the compressed surrounding renal parenchyma (Fig. 1.38) [65].
On imaging, they commonly appear heterogeneous due to hemorrhage, necrosis, and cysts. Calcification can be found in 10–15 % and gross fat is seldom detected on CT. Clear cell RCCs are typically hypervascular on contrast-enhanced CT and show earlier and stronger enhancement than other subtypes. Characteristically, they enhance similarly to or stronger than renal cortex at early arterial or corticomedullary phase of contrast-enhanced CT (Fig. 1.2). A recent study reported that multiphasic MDCT could discriminate clear cell RCC from oncocytoma, papillary RCC, and chromophobe RCC with the accuracies of 77 %, 85 %, and 84 %, respectively, because clear cell RCCs exhibit significantly greater enhancement at the corticomedullary phase [66].
On MRI, clear cell RCCs usually show high SI on T2WI and iso SI on T1WI to that of the renal parenchyma (Fig. 1.11). Hemorrhage and necrosis make the tumor appear heterogeneous on T2WI. Pseudocapsule of the mass appears as low-signal rim at the periphery of the mass. Considerable signal drop within the solid portions of a clear cell RCC on opposed phase MR images can be detected in up to 60 %, due to the presence of intracytoplasmic fat. Dynamic contrast-enhanced MRI can provide important information in differentiating from other subtypes. A study reported that tumor-to-cortex enhancement indexes at the corticomedullary and nephrographic phases of dynamic contrast-enhanced MRI were the largest for clear cell RCCs and the smallest for papillary RCCs. SI changes on corticomedullary phase images was the most effective parameter for the differentiation [67].
Papillary RCC
It accounts for 10–15 % of all RCC and the second most common subtype. There are two histomorphologic subtypes (type 1 and 2), and type 1 tumors are typically of a lower stage and grade than type 2 tumors and associated with a better prognosis. Bilateral or multifocal tumors are more common in papillary RCC than in other subtypes, which is especially common in hereditary syndromes. Papillary type is the most common in RCCs arising in patients with ESRD. Long duration of dialysis may be a predisposing factor (Fig. 1.39). It is usually solid, slow growing, and in intrarenal location in 70 % at presentation [65]. On US, it usually appears as a homogeneous mass of variable echogenicity and hypovascular on Doppler US. On CT, high attenuation within tumor on unenhanced images may be visible due to hemorrhage, even in small tumors. Fat is rarely detected. Papillary RCCs show weak, homogeneous, and persistent enhancement on dynamic contrast-enhanced images (Fig. 1.40). These findings are not different between type 1 and 2 tumors [68]. On MRI, they show homogeneous low SI compared with the cortex on T2WI. This low SI on T2WI, which may be due to hemosiderin deposition, hemorrhage, or necrosis, is an important MR characteristic in differentiating from clear cell RCCs [69] (Fig. 1.11). Clear cell RCCs usually show heterogeneously high SI on T2WI and strongly enhance on corticomedullary phase, but papillary RCCs enhance minimally on early phase and less than renal parenchyma on nephrographic phase.
Fig. 1.39
Papillary RCC in ESRD. Contrast-enhanced CT shows a small hypervascular mass (arrow) in the left kidney, suggesting RCC. Note atrophic kidneys
Fig. 1.40
Papillary RCC. (a–c) In three-phased contrast-enhanced CT, a mass (arrow) in the left kidney is slightly hyperattenuating on noncontrast CT (a) and mildly enhancing both in corticomedullary (b) and in nephrographic (c) phase
Chromophobe RCC
It is the third most common subtype and accounts for approximately 4–11 % of RCCs. There is no gender preponderance, and it is most common in the sixth decade of life. It has the best prognosis among RCCs, although large tumors may be accompanied by hepatic metastases. On US, chromophobe RCCs tend to be homogeneously echogenic. On CT, and MRI, they enhance homogeneously and mildly. This homogeneous enhancement is also visible in even large tumors (Fig. 1.41). On dynamic contrast-enhanced images, they enhance intermediately on corticomedullary phase and show variable enhancement (early washout or constant enhancement) on delayed phases. Fine reticular enhancement has been reported on corticomedullary phase in 70 % of cases, which may be helpful for the differentiation from other subtypes [65]. Spoke-wheel pattern of enhancement has been also described, similar to the enhancement pattern of oncocytoma. Oncocytomas share similar histologic features with chromophobe RCCs and may show similar imaging findings [70]. On MRI, chromophobe RCCs may show signal intensity similar to that of clear cell RCCs or might appear low SI on T2WI compared with renal parenchyma [71].
Fig. 1.41
Chromophobe RCC. (a–c) Three-phased contrast-enhanced CT show a mass (arrow) in the left kidney, which is homogenous and mildly enhancing ((a) noncontrast scan, (b) corticomedullary phase, (c) nephrographic phase)
Multilocular Cystic RCC
Multilocular cystic RCC is a rare subtype and constitutes 1–4 % of all RCCs. The incidence is more common in males than females and higher in middle-aged patients (around 50 years old). Its prognosis is usually favorable, and the cure can be almost achieved by nephrectomy. It appears as a multilocular cystic mass on imaging with septa of variable thickness. It is separated from renal parenchyma by a fibrous capsule, and the septa and the capsule enhances mildly or minimally on CT and MRI (Fig. 1.7). They may show enhancing nodular thickening and can contain calcifications in 20 %. They appear as cystic masses of variable Bosniak category from IIF to IV, and the higher the category, the larger the volume of malignant cells and/or vascularized fibrous tissue [72].
Collecting Duct Carcinoma
It is a rare and highly aggressive subtype, accounting for less than 1 % of all RCCs. Metastasis is present at the time of diagnosis in one-third of the patients. The prognosis is very poor, and two-thirds of patients cannot live for more than 2 years after the diagnosis. It is more common in males (male to female ratio: 2:1) and the mean age is 55 years. Its typical imaging appearance is an infiltrative tumor with the epicenter in the medullary portion of the kidneys near the renal pelvis. US appearance is nonspecific and usually shows heterogeneous echogenicity due to necrosis and hemorrhage. CT and MRI findings are also nonspecific, especially in larger tumors, and the differentiation from other subtypes is often difficult. On CT, it is poorly enhancing and may have calcifications. The enhancement pattern is heterogeneous or predominantly peripheral. Its infiltrative pattern of growth preserves renal contour (Fig. 1.42). On MRI, it shows variable SI on T1WI and usually low SI on T2WI. Heterogeneous SI is common due to necrosis, hemorrhage, and calcification, and a cystic portion may be visible in 50 % [65, 73].
Fig. 1.42
Collecting duct carcinoma. Contrast-enhanced CT shows a large, ill-defined mass (large arrow) in the left kidney. Renal contour is preserved, and enlarged regional lymph node (black small arrow) and renal vein thrombus (white small arrow) are visible
Renal Medullary Carcinoma
It is also rare, accounting for less than 1 % of all RCCs. It occurs exclusively in patients with sickle cell trait. The patients are almost always young, aged between 11 and 40 years. The male-to-female ratio is 2:1. Medullary carcinomas are aggressive tumors with early local invasion and distant metastasis and the prognosis is unfavorable. On imaging, they appear as ill-defined and infiltrative masses centered on the renal medulla. The renal contour is usually persevered, and caliectasis is commonly associated. On CT and MRI, they are hypovascular and heterogeneously enhancing. They show heterogeneous SI on T2WI due to necrosis and hemorrhage [65, 74].
Mucinous Tubular and Spindle Cell Carcinoma
It has been often diagnosed as a sarcomatoid RCC or a renal sarcoma but newly classified as a distinctive subtype. Its clinical course is indolent and the prognosis is favorable. Imaging findings are nonspecific.
Xp11.2 Translocation–TFE3 Gene Fusion Carcinoma
It is also a newly classified subtype and accounts for 20 % of RCCs in the first and second decades of life. The prognosis is favorable, although it is discovered in the advanced stage. Its imaging findings are rarely described in the literature, and reported CT and MRI findings include hyperdense and hypovascular mass on CT and hypointense on T2-weighted MR images (Fig. 1.12). The imaging finding may be similar to papillary RCC due to histopathological resemblance [75].
Hereditary RCC Syndromes
Von Hippel–Lindau syndrome is the most famous hereditary RCC syndromes, in which multiple RCCs are developed in bilateral kidneys associated systemic syndromes including retinal angiomas, central nervous system hemangioblastomas, and pheochromocytomas (Fig. 1.43). In Birt–Hogg–Dube’ syndrome, renal tumors including chromophobe RCC, oncocytoma, or hybrid tumors are associated with skin lesions or lung cysts. Hereditary syndromes associated with papillary type include hereditary papillary RCC (type 1) and hereditary leiomyoma RCC (type 2). Recently, PTEN hamartoma tumor syndrome (PHTS) is newly reported as a hereditary syndrome associated with papillary RCC [65, 76].
Fig. 1.43
Von Hippel–Lindau syndrome. (a) Contrast-enhanced CT shows a large mass (large arrow) in the left kidney. Note bilateral adrenal masses (small arrows). (b) Another small mass (arrow) suggesting RCC is also found in the right kidney
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