These types of pathology do not need conservative surgery and segmentectomy. The only exception is Ask-Upmark kidney or segmental hypoplasia. This maldevelopment forms cortical scars, sinking, and wrinkling of the underlying pyramids, and dilation of relative calyces. Histologic examination of this abnormal metanephric differentiation shows microcysts and the absence or glomerular paucity. Urethral valves and vescicorenal reflux, with or without infection, frequently coexist. This demonstrates the acquired maturation of the lesions, although already present in intrauterine life. Obviously conservative surgery and segmentectomy could be considered when the segmentary form of the hypoplasia is associated with normal unaffected parenchyma. It is also obvious that prior to renal conservative surgery, any other malformations (urethral, ureteral) must be corrected, if present [104–109].

Some types of pyelonephritis could arise mainly or exclusively in a single area of the kidney. In these cases, when surgery is indicated, renal segmentectomy could be the best choice.

Among those conditions, pyelonephritis, the xanthogranulomatos type, also known as renal pseudotumor, has been observed in thousands of cases worldwide despite not being a frequent disease, and has attracted the attention of urologists for presentation, modality, and treatment choice, which often proves to be surgical.

As is known, it is a granulomatous form with typical foamy cells that can evolve silently, but that routinely manifests with symptoms of infection, general weakness, toxicosis, and local and general complications that can sometimes be very serious, such as septic syndrome, amyloidosis, parietal and visceral fistulae, renal vein thrombosis, and so on. Bilateral forms are exceptional. The regional or segmental forms give rise to a strong suspicion of the presence of a tumor, due to the unaffected integrity of the parenchyma. Thus a careful differential diagnosis, both clinical and radiologic, is necessary. The persistent or relapsing history of a urinary infection, the bacterial peculiarity (proteus, pseudomonas, coli), the typical urinary cells, the associated urinary stones, the sequence of previous sonographic examinations, as well as the precision of imaging tests are all useful or even indispensable for obtaining the correct preoperative diagnosis.

When surgical conservative treatment seems necessary, segmentectomy could be considered given the good results that can be obtained with regard to the healthy parenchyma. This is the case in infantile forms or in medullary localized forms in adulthood.

Though exceptional, some forms of conservative surgery for renal xantogranulomatosis caused by bilharzia have been described. Routinely renal lesions of bilharziosis consist of ureterohydronephrosis due to vesico-ureteric parasitic invasion. Nevertheless, cases of true parasitic renal xantogranulomatosis due to schistosomas are rarely missed. In a minority of those reported cases a good portion of the kidney was sound, thus allowing for conservative surgery [113, 114, 117].

This malformation consists of the dilation of a calyx with consequent tributary parenchyma destruction, caused by the compressive ischemia, which could also affect the neighboring parenchyma. The hydrocalyx is drained by the obstructed infundibulum. It is still a matter of disagreement whether or not the congenital forms are due to calyceal neck achalasia and if the acquired form could be caused by something capable of creating an obstruction such as prolonged spasms, fibrosis, etc. Hydrocalyx is clinically relevant only for complications, such as hemorrhage, infections, and painful stones.

According to the nature of the symptoms and the seriousness of the renal harm, when endoscopic treatment fails, partial ablation is indicated and typically segmentectomy as well.

This maldevelopment concerns a small calyx eventration lying within the renal parenchyma and communicating with the main collecting system through a narrow channel. The diverticulum is lined by a transitional epithelium, which appears to be because of the absence of reabsorption of third- or fourth-generation ureteric branching. It is often asymptomatic and clinically irrelevant, but it could be a sign of obstruction, stones, or suppurative flogosis requiring surgical treatment. Endoscopic, percutaneous, or minimally invasive pathways are frequently available, but if the corresponding renal lobe is hopelessly compromised, segmentectomy should be the treatment of choice.

This malformation is a medullary papilla hypoplasia with consequent dilation, expansion, and apparent multiplication of calyces without obstruction. The pelvis and ureters are normal. The condition is due to an anomaly in the development of the ureterogenic blastema in the collecting ducts. It would seem to be supported by late channeling of the high ureter, to which the ureteral gem branches are connected via the metanephric blastema. The delay creates some sort of obstruction of primitive glomeruli when they start to work. According to the general concept of the ureterogenic theory, the epithelial structure also induces the support of scaffolding organization. Consequently the failure of the uretrogenic blastema prevents development of the pyramidal structure.

Megapolicalycosis is thus congenital. The male/female ratio is 6:1, and the White population are most commonly affected. In males it is bilateral and in females it can only be segmentary.

The medullary portion is hypodeveloped with a crescent or sickle shape. The collecting ducts are not dilated but are shorter than normal and are transversely oriented compared to the cortico-medullary junction. The renal function remains normal.

In the majority of cases the disease is discovered casually. Surgical indication is quite rare or exceptional, as it is reserved for local, sectorial complications like infections or stones. Segmentectomy involves improving the outcomes of those lobar complications.

An infundibulo-pelvic stenosis is probably caused by an anomaly in the ureteral gem. It is often associated with a cystic dysplasia of the kidney. The stenosis grading is variable. A focal form that involves only one or two calyces may exist, but commonly the disease is bilateral and associated with vesico-renal reflux.

Histologic examinations of infundibular renal stenosis [38, 43] have shown a hyperplasia of smooth muscles within the submucosa with scattered rare interstitial spindle cells that are CD117 positive, similar to the cells responsible for peristaltic pacemaker activity of the gastrointestinal tract. The presence of CD117 cells suggests that the calyceal narrowing is due to renal hyperplasia and not to leiomyomatosis. However, which of them is the hyperplasic stimulus is unknown.

This condidion is frequently asymptomatic and the diagnosis is achieved on the basis of the presence of hypertension, infection, and lumbar pain.

An indication for a conservative surgery, such as a segmentectomy, is put forward based on its localization, renal function, and symptoms.

Conversely, due to the superior calyx dilation being the longest, it is the only one to be caused by a vascular compression, which is more frequently arterial, and also known as Fraley syndrome [79], for which normally there is no question of a segmentectomy (Fig. 5.1).

There are conditions of the reno-ureteric duplicate collecting systems in which the ablation of one of the two segments is necessary. The reason for surgery is commonly aplasia or another pathology of the parenchyma, which has been drained by the supernumerary excretory pathway share. Such malformative conditions are generally recognized in childhood and, if complicated, surgery (strictly that of ablation) is not compulsory.

The collecting system duplicity occurs in just under 1 % of births and in the majority of cases it is asymptomatic. It may be complete or partial in the pelvis and ureter, depending on whether the ureteral gem branched to join the metanephric blastema at an early or late stage in development. It seems to be a dominant autosomal form with poor penetrance. In 12 % of cases it is associated with other urinary anomalies, 50 % of which are on the same side and to which the causal role of complications and related symptoms are attributed. In a majority of cases (88 %) there are no true complications.