# Fetal Megacystis: A New Morphologic, Immunohistochemistryistological and Embiogenetic Approach
## 4 Discussion  
The kidney and urinary tract develops from two different embryonal sheets: kidneys, ureters and bladder trigone from the mesodermal sheet, and bladder and urethra from the endodermal sheet. The bladder develops from the fourth to seventh week of gestational age from the urognital sinus. At the ninth week, after the involution of cloaca, the urognital sinus opens into the amniotic cavity. CAKUT represent up to 20%-30% of all major congenital pre and postnatal defects [3], including both sporadic and familial cases and associated anomalies, such as syndromic malformations. Among all CAKUT, our paper focuses on mainly bladder and urethral malformations. Isolated bladder anomalies, such as bladder agenesis, complete/incomplete duplication or bladder extrophy, are rare. Instead, morphologic bladder anomalies, known as megacystis, are more frequent and related to urethral or neuromuscular anomalies. Fetal bladder is defined as megacystis if its longitudinal diameter is \(>\)10% of crown-rump length in different gestational ages. In the first trimester, the longitudinal diameter may be more than 6 mm. Prenatal detection of a larger bladder could suggest an outlet obstruction, mainly due to urethral obstruction, but also other congenital complex malformations of the kidney and urinary tract. Moreover, in the case of megacystis, microcolon syndrome as well as neuro-muscular malformations should be considered. Figure 8: Case 2, PBS. Immunohistochemical staining in bowel: SMA (**A**) in two longitudinal side-by-side muscular layers (arrow), S100 (**B**) and WT1c (**C**) were not expressed. Figure 7: Case 2, Prune-Belly syndrome (PBS). Immunohistochemistryistochemical staining in bladder: SMA (**A**) in a thin, longitudinal, muscular layer (arrow), S100 (**B**) only in peripheral nervous fibers (arrow), WT1c (**C**) negative. PUV has been considered the most common cause of urethral obstruction in newborn males, while obstruction of the anterior urethral valve is less common and its complications are less severe than PUV. Three types of PUV have been described: type 1, the most common (95%), with two mucosal folds from the bottom of veromontanum to the membranous urethra; type 2, with mucosal folds extending along posterolateral urethral wall from the ureteric orifice to the veromontanum; type 3, with a circular diaphragm with a central opening in the membranous urethra. In any type of urethral obstruction, the high intravesical pressure leads to defects in the muscular differentiation, with fibrotic tissue interposed among muscular fibers and a thickened bladder wall [1,2]. PBS occurs mainly in baby or infant males (97%) and is characterized by atrophy of the anterior abdominal wall due to muscular absence, anomalies in the urinary tract, such as megaureters and bilateral hydronephrosis, and testicular agencies or cryptochidism. More often, the bladder shows thickened walls with dilated ureteral orifices in the vesical trigone and vesicoureteral reflux. However, bladder histology is variable, showing both increased and decreased muscular fibers, with or without interposed connective tissue. In a previous study, [PERSON] et al. [4] described PBS with increased muscular thickness of the bladder in a case of intravesical obstruction, while a more recent work [5] reported PBS with decreased muscular thickness of the bladder in a case of urethral obstruction. In the latter case, the higher intravesical pressure, together with atrophy of the abdominal wall, could cause decreased muscular thickness, increased fibrobl activity and overproduction of collagen type I, inhibiting muscular contractility and electrical impulse diffusion through the muscular layers. Megacystis/megaureter syndrome is characterized by megacystis with thinned walls, vesicoureteral reflux, bilateral hydroureters and hydronephrosis and, often, dysplastic kidneys. It is frequently associated with microcolon and functional obstruction of the gastrointestinal and urinary tracts [6].