Surgical therapy for these cysts is not frequently indicated, is nearly exclusively for atypical or hemorrhagic or suppurated forms of puncture treatment [57]. In such cases segmentectomy, rather than extracapsular removal, can be considered when and if nearly all of the segment is involved (which is exceptional).

This is a rare kind of non-hereditary, organogenetic, dysembryogenetic, malformative disease, considered similar to benign neoplasia. It is relatively rare, but not excessively so given that recently five cases have been reported in Piedmont alone (an Italian region of 4,400,000 inhabitants) [62, 65]. Part of the renal parenchyma is replaced by a cluster of cysts that do not communicate between themselves and are not connected with the pelvis and calyces. A capsule envelops the cluster. It is always monolateral, and almost exclusively in women. What remains of the renal parenchyma is normal. There are often other malformations.

An infantile form also exists. It is generally considered to be one of the following: benign cystic Wilms’ tumor, cystic nephroblastoma, or differentiated nephroblastoma. The diagnosis of this is generally on the basis of the presence of an abdominal mass.

Surgical treatment is by no means the rule, as especially in adulthood, patients are often symptomless, so surgery is reserved for large, complicated masses protruding in the abdomen. When the cyst bunch concerns one or more lobes, complicated by inflammation or hemorrhage, segmentectomy is indicated and the remainder of the kidney is considered normal and sound. Obviously preoperative or intraoperative tumor lesions have to be excluded.

As mentioned earlier, the cystic nephroma is often associated with other genitourinary malformations or the pathologies of different organs.

A possible, though very rare, association with endometriosis makes the diagnosis even more difficult, as in the case of C. Boccafoschi, in which this disease was associated with cystic lymphangioma involving the bladder and sigmacolon. The lymphangioma was presumably caused by a diffuse lymphatic obstruction at the pelvis level, which consequentially created lymphatic dilations and cysts. A type of lymphangioma was then at least partially acquired [65].

As mentioned above, since multilocular renal cysts may be considered neoplastic lesions, this was suggested as a more appropriate name [47]. This definition must be reserved particularly for cystic tumors that have been formed from entirely differentiated tissues, without blastema, or other embryonal elements. The designation of “nephroblastoma partially differentiated” defines cystic lesions as lacking in a solid, nodular area, while blastema or other embryonal tissues are present in cystic septa. They are not especially aggressive and never result in metastasis.

The reason for the lesion being known by such a variety of names, such as multilocular renal cysts, partially polycystic kidney, renal cystadenoma, polycystic nephroblastoma, differentiated nephroblastoma, and cystic nephroma, is the result of different etio-pathogenetic interpretations. Essentially there are two contrasting theories: neoplastic and dysplastic. The first seems to be more accredited today, supported by the fact that in dysplasic skeletal muscle, spots of metanephric undifferentiated blastema and immature mesenchyme such as that of nephroblastoma have never been found. The absence of typical elements of dysplasia, such as cartilage and embryonal ducts, support the neoplastic hypothesis.

The dysplastic-malformative theory relies on the idea of an autonomous vascularization that is independent from the renal vessels and originates in the lumbar vessels. This contention has appeared in the same literature and it assumed that cystic nephroma is a species of renal sequestration similar to pulmonary sequestration [70]. The latter is also a cystic malformation of the lung that does not communicate with the bronchial system and pulmonary vessels, but is nurtured by a systemic few vessels that it captures from the rest of the lung.

Another group of renal neoplastic cysts is the group of multilocular cystic renal-cell carcinomas, which represents a sub-group of renal cell carcinomas with proper macro- and microscopic characteristics. The features of these cysts include a variable quantity of neoplastic clear cells, with nuclear grade 1, and small or no mitotic activity. The cystic wall is fibrotic and often has no epithelium. Tumors are diploic at flux-cytometry and experience very low proliferative activity. Joshi et al. [47] believe this group of cyst to be a variant of low-grade clear cell renal tumors.

Finally, in order to avoid confusion, it is necessary to remember that the diagnosis of cystic nephroma is mainly based on the following characteristics: unilateral, isolated, multilocular, and unconnected to the pelvis or calices. The different cysts do not communicate with each other, and all the have a lined, defined epithelium, whilst normal and mature renal tissue is absent in them, and, importantly, the adjacent kidney is normal [69]. With regard to conservative therapy and then renal segmentectomy, it is very important to reach the diagnosis preoperatively, demonstrating that a good amount of normal paremchyma can be saved. One should also be aware of the possible presence of adenocarcinama or nephroblastoma foci in the lesion; however, this does not exclude conservative surgery with favorable results [67, 68].

About 50 cases of this disease have been published. They are differentiated from polycystic autosomic diseases (recessive or dominant) by the absence of familiarity, unilaterality, and segmentarity. This is a benign form that does not have the tendency to evolve into renal insufficiency and for which surgical treatment is not generally necessary, except in cases of space-occupying masses and pain [72].

The literature provides examples of nephrectomies being carried out due to the suspicion of the presence of a tumor, despite a good biopsy result. The anatomic specimen showed that the normal parenchyma was lesion free. Thus we now know that when a surgical indication exists, segmentectomy or another partial resection can be considered.

Two typical cyst-tumor associations are those of von Hippel-Lindau and tuberous sclerosis. Von Hippel-Lindau disease is transmitted by an autosomal dominant character. Cerebellar and retinal hemangioblastomas, pancreatic cysts and carcinomas, and renal cysts and tumors represent such a serious problem]. that the issue of the cyst itself is completely non-existent. Surgical treatment, which takes into account the complete or partial nature of the tumor, will be indicated. It is well known that maximum effort should be extended toward preserving the not-yet invaded parenchyma. For tumors that are less than 3 cm in size, nonsurgical renal-spearing strategies (radiofrequency, percutaneous ablation, and selective trans-catheter arterial embolization) have shown promise in short-term trials. For tumors that are more than 3 cm in size, conservative surgery, such as partial nephrectomy or even segmentectomy, should be considered.

In multiple tuberous sclerosis, which is transmitted via an autosomal dominant character, the hamartomas of the skin, brain, retina, skeleton, lungs, and kidneys are often associated with cysts. Sometimes the cysts are big and cause arterial hypertension. Indication for surgery is exceptional and nearly always based on the angiomyolipomas situation (present in 50 % of cases) and its clinical scenario is as follows: hematuria, hemorrhage, flank-loin pain, and life-threatening retroperitoneal hemorrhage. Bleeding complications create an emergency and require urgent surgery. For this reason, conservative treatment, which would otherwise always be desirable, becomes in practice impossible. In that sense renal segmentectomy in cases of tuberous sclerosis represents just a theoretical indication.

It must be remembered that the first manifestation of tuberous sclerosis, though extremely rare, being unilateral, could be segmental cysts found in children, as in the case of the segmental cysts reported in 1997 by Wel Lara et al. [73].

Indeed, with regard to the relationship between renal cysts and tumors, interesting research is beginning to clarify the co-responsibility of proliferative activity of the cystic epithelium and genes regarding the induction of tuberous sclerosis. In this regard it was strongly suspected that the two major genes of tuberous sclerosis and polycystic kidney disease, TSC2 and PKD1, respectively, are adjacent in chromosome 16p, 13.3. It is on this basis that Sampson et al. believe that PKD1 has a role in the etiology of tuberous sclerosis [79].

Apart from von Hippel Lindau and tuberous sclerosis diseases, with regard to the cyst/tumor association, clinically the problem of identifying the presence of neoplastic tissue in cysts appears predominantly in complex cysts, where the occurrence of malignancy is greater. Imaging with radiologic follow-up and guide biopsy is able to reach the correct diagnosis and avoid unnecessary surgery in 39 % of cases of cystic renal masses, the second category of Bosniak, according to Hansinghani et al. [80]. Apart from complex cysts, CT imaging shows some cysts with unusual content, now known as hyperattenuating renal masses. These cysts are wholly or predominantly filled with CT attenuation, higher than the surrounding parenchyma. Protein or iron concentration, hemorrhage, colloids, infections, and occasional iodine accumulation are the most frequent reasons for the hyperattenuation of simple cyst content. Hyperattenuating renal masses may also be constituted by hematoma, vascular aneurysm, malformations, malignant cysts, benign hyperattenuating cysts, and other hyperattenuating solid masses. As a consequence, the importance of recognizing the etiology and pathogenesis of the lesion is essential for correct clinical diagnosis. In the majority of cases the cysts are benign, and it must be emphasized that when neoplastic, the small cysts, with homogeneous enhancement hyperattenuating, should be considered to be of benign origin [80, 81].