Diagnosis

The majority of patients are asymptomatic, with incidental diagnosis on imaging performed for other indications. The differential diagnosis includes renal or parapelvic cysts, hydrocalycosis (hydronephrosis of a calyx) secondary to infundibular stenosis, cystic tumors, and solitary abscess. In appropriate clinical settings, cortical cavitation secondary to renal tuberculosis has similar appearance [12]. In children, calyceal diverticula commonly present with UTIs and association between calyceal diverticulum and vesicoureteral reflux should be ruled out [19, 20].

The workup includes urinalysis, complete blood count, basic metabolic panel, and imaging of the abdomen. A renal ultrasound or noncontrast computed tomography (CT) scan is typically performed. Renal ultrasound will accurately diagnose calyceal diverticulum in 80% of cases [21] (Figure 28.1). The diverticulum without stones will have appearance and echotexture similar to renal cysts. When echogenic material is present, the patient is scanned in different positions to demonstrate gravitational changes of the content, a tell‐tale sign of calyceal diverticulum [3]. The classic ultrasound finding of “milk of calcium” is a colloidal suspension of precipitated calcium crystals [22]. The milk of calcium will appear as a meniscus‐like, semilunar calcification that changes position on upright and lateral decubitus radiographs [23]. Calyceal diverticula are seen on noncontrast CT as a small, round, low‐attenuation area adjacent to the calyx or as a dilated outpouching from the collecting system containing a stone [24] (Figure 28.2).

Prior to any treatment, the location of the diverticulum and communication with the rest of the collecting system should be confirmed with a CT urogram or an intravenous pyelogram (IVP). Most calyceal diverticula will opacify if they have a significant communication with the collecting system [8]. Since the diverticulum itself is nonsecretory, the opacification will occur later in the examination as it is filled in a retrograde fashion from the collecting system, necessitating delayed images [3, 25] (Figure 28.3). A retrograde pyelogram can be helpful in locating the neck of the diverticulum. Where the calyceal infundibulum is obstructed, the diverticulum will not opacify with contrast administration and becomes difficult to differentiate from a complex renal cyst. This finding is important for surgical access planning. Notably, the failure to demonstrate the diverticular neck does not detract from the diagnosis [11].

Treatment

Patients with asymptomatic calyceal diverticula do not require treatment. Pain, recurrent UTI, hematuria, symptomatic calculi, or progressive renal damage are indications for intervention [7]. Traditionally, open marsupialization and fulguration of the diverticular cavity or partial nephrectomy were performed. Nowadays minimally invasive options for symptomatic calyceal diverticula include SWL, URS, PCNL, and laparoscopy. Treatment options depend on diverticulum location, stone burden, and size [26].

SWL for the treatment of calyceal diverticula is controversial. Although at short‐term follow‐up SWL provided symptomatic improvement in 36–70% of patients, stone‐free rates were low at 4–20% [27, 28]. The highest reported stone‐free rate remains suboptimal at 58% [29]. With longer observation, patients initially rendered symptom‐free with SWL will become symptomatic and require retreatment [27]. Thus, SWL is rarely considered as monotherapy for calyceal diverticula. To prevent stone recurrence, eradication of the diverticulum should accompany stone removal, a goal that is rarely achieved with SWL [30, 31]. Furthermore, while SWL may be effective in stone fragmentation, the passage of these fragments remains a concern. The narrow diverticular neck that is hypothesized to cause stone formation through stasis in the first place can prevent fragment clearance [3].

Ureteroscopy is more effective at stone clearance than SWL. It is minimally invasive and can allow ablation of the diverticular cavity at the same time. Retrograde URS is a reasonable option for selected patients with a diverticulum in the upper or middle portions of the kidney when the stone burden is small and the diverticular neck is short and easily accessible [3, 30, 32]. Lower pole calyceal diverticula are often at an acute angle that precludes retrograde management. Identification of the diverticular neck can be difficult with a retrograde approach and may account for the lengthy operative times (1.25–4 hours) reported in some URS series [32, 33]. In one series the ostium could not be identified at all in a third of patients [12]. Injection of contrast or methylene blue (with subsequent washout from renal pelvis followed by the slow drainage of the dye from the diverticular ostium) can be useful in identifying the ostium [34]. The diverticular neck is then incised or dilated, allowing stone clearance and cavity ablation with either a holmium:YAG laser or a Bugbee electrode. Stone‐free rates for URS range from 19% to 90%, but diverticular obliteration is as low as 18%; furthermore, a significant number of patients demonstrate residual symptoms and require retreatment [31, 33, 35–38]. Bas et al. compared 29 PCNL with 25 URS cases, with similar stone‐free rates but higher major complication rates in the PNL group; however the stones in the PNL group were larger [39]. Auge et al. compared 22 cases of PCNL with 17 URS cases and concluded that PCNL was universally better than URS for all stone locations and should be used as a primary modality for calyceal diverticular stones [36].

Laparoscopy is suitable for large anterior diverticula with a thin layer of overlying parenchyma and significant stone burden [40, 41]. Diverticula in ectopic kidneys, where a percutaneous approach will be hampered, are another indication. However, the laparoscopic approach is more invasive than PCNL with lengthy operative times (up to 2.5 hours) even in experienced hands, and should only be considered in select cases [41–43].

Percutaneous treatment of calyceal diverticulum calculi achieves high stone‐free rates (87.5–100%) and allows simultaneous obliteration of the diverticular cavity in 76–100% [25, 27, 31, 44–49]. Over 90% of patients report symptomatic relief with percutaneous treatment [27, 36, 44–46, 50], with durable 100% success rates at 38 months follow‐up in another study [46]. In a report from Kim et al., operative times were <60 minutes and 20 of 21 patients were sent home tubeless on postoperative day 1 [48]. Typically, percutaneous access is performed directly into the calyceal diverticulum to allow use of a rigid nephroscope as successful treatment of stone‐containing diverticulum is contingent on complete stone removal [48]. Direct puncture of a small or upper pole diverticulum can be difficult, requiring puncture of a neighboring calyx. The diverticulum is then entered indirectly by perforating the wall of the diverticulum or by entering in a retrograde fashion through the diverticular neck [51]. However, this “indirect assess” technique has a lower rate of diverticular cavity obliteration (50% vs. 79%) [45, 52]. Finally, percutaneous balloon dilatation of calyceal diverticular infundibula in the absence of stones has also been described [53].

Controversy exists regarding optimal management of the diverticulum following complete stone removal. An existing communication to the collecting system can be dilated and stented or created anew (neoinfundibulotomy), in an effort to promote drainage [27, 38, 45, 47, 50]. Both techniques carry risk of bleeding and require the placement of a nephrostomy tube for a prolonged period to ensure patency. Another treatment strategy is to fulgurate the diverticulum. This can be achieved percutaneously, without ureteral catheterization or infundibular cannulation, with 87.5–100% diverticular ablation rates [46, 48]. Although calyceal diverticulum is lined by a nonsecretory endothelium, most authors advocate fulguration at the time of PCNL [30, 33]. Dilation or incision of the diverticular neck without fulguration results in complete ablation of the diverticulum in only 30% of cases [54], in contrast to the 76–100% ablation rate when fulguration is performed [27, 45, 46, 55]. Others suggest that diverticular wall trauma from the percutaneous dilation process itself is sufficient to ablate the diverticular lumen [44]. If fulguration is to be performed, avoiding infundibular dilation will maximize the chance of diverticular obliteration. Krambeck and Lingeman compared dilation of the infundibular tract with cavity fulguration alone. The “fulguration only” technique had a higher initial stone‐free rate (94.2% vs. 77.3%) with shorter length of stay. The diverticulum either disappeared or reduced in size in 89% of patients who had follow‐up IVP at three months [56].

Technique

The procedure is preceded by careful review of imaging to assess the degree of diverticular filling. The percutaneous approach is typically achieved with biplanar fluoroscopy and is thus reliant on visualization of the radiopaque target [57]. If the diverticulum does not fill retrogradely with contrast and/or if the stone is radiolucent, the following steps can be taken. First, contrast can be instilled into the diverticular cavity via a retrograde ureteral catheter (Figure 28.4). Care must be taken to avoid overfill and contrast extravasation, as this makes subsequent fluoroscopic targeting difficult. Second, if the diverticulum does not readily fill with contrast due to stenosed infundibulum, a CT‐ or ultrasound‐guided pre‐PCNL opacification of the diverticulum by interventional radiology is an option [25]. A 20G spinal needle is manipulated under radiographic guidance into the diverticulum. Iodinated contrast is gently instilled until resistance is encountered and kidney–ureter–bladder (KUB) imaging is performed to confirm opacification of the target (Figure 28.5). The patient is then transported promptly to the operating room as too long a delay may permit absorption of the contrast and loss of the target. Lastly, ultrasound guidance can be utilized [58]. Unfortunately, it is difficult to monitor guidewire manipulation with ultrasound imaging.

If the target diverticulum is radiopaque, a single‐stage procedure is performed where percutaneous access is directed straight onto the stone [48] (Figure 28.6). The patient is anesthetized and positioned prone without an external ureteral catheter. A C‐arm is used to visualize the diverticular calculi. When possible, a direct infracostal puncture (to reduce risk of pleural injury) is performed using an 18G diamond‐tipped needle and a biplanar fluoroscopic triangulation technique [59]. A 0.035‐inch J‐tipped movable core guidewire is coiled inside the diverticular cavity, taking care to avoid wall perforation with the stiffer portion of the wire. The flexible distal end of the movable core J‐wire can be adapted to the size of the diverticulum, while the wire proximal to the moved core remains stiff enough to function as the working wire. With the J‐wire in place, an 8/10 Fr coaxial dilator is passed over the J‐wire in a sequential fashion. The 8 Fr dilator is removed and a second 0.035‐inch J‐tipped movable core wire is coiled inside the diverticulum and used as the safety wire. The tract is balloon dilated over the working wire, carefully placing the balloon dilator and the wires to avoid perforation of the back wall. A 30 Fr Amplatz sheath is then passed over the balloon dilator under fluoroscopic guidance. The taper on the distal end of the balloon dilator will preclude placement of the sheath directly into the diverticular space unless the diverticulum is large. Next, an offset 24 Fr rigid nephroscope is placed inside the access sheath using normal saline irrigation. Alligator forceps (11 Fr) are used to manually dilate the part of the tract immediately adjacent to the diverticulum, allowing for advancement of the scope and subsequently the sheath into the diverticular lumen. Once inside the diverticulum, ultrasonic lithotripsy or grasping forceps are used to remove the stone burden. Stone culture is obtained by using grasping forceps to transfer a stone fragment directly into the culture cup, where it is ground with a sterile hemostat. After removal of all stone material the entire cavity should be inspected for presence of a flattened renal papilla, indicating an obstructed hydrocalyx rather than a calyceal diverticulum (see Video 28.1).

The irrigant is switched to 1.5% glycine (or sorbitol 2.7% with mannitol 0.54%) to fulgurate the diverticular lining with a resectoscope and a rollerball electrode. Low‐energy electrocautery (20 W coagulation, 0 W cut) settings are used. The tip of the rollerball electrode can be bent to aid fulguration of difficult‐to‐reach areas in the diverticulum or a Bugbee electrode can be used. Fulguration with holmium:YAG laser has also been described [60]. The infundibular communication is neither assessed nor dilated. An 18 Fr red rubber catheter or, in larger cavities, a 10 Fr Cope loop catheter is placed in the cavity. Proper placement of the drainage tube is confirmed by contrast instillation under fluoroscopy. If the diverticulum is small, the red rubber catheter acts as a perinephric drain, as it usually becomes dislodged from the diverticular cavity. The drainage tube can be removed on postoperative day 1 if drainage is minimal. Occasionally, if the communication with the renal collecting system is large, considerable (i.e. >100 ml) drainage from the nephrostomy tube may occur. In this situation the nephrostomy tube is left for one week to allow the tract to mature.