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MMIHS prevalence is unknown but the disease has been reported in 230 patients, of which 71% are females.

Enlarged and nonobstructed bladder is the first manifestation of MMIHS and can be detected prenatally. It results in abdominal distension, which is an early constant finding. Usual clinical presentation is similar to other neonatal intestinal obstructions: bile stained vomiting and failure to pass meconium. Patients show various visceral anomalies of the digestive tract including microcolon, malrotation of the gut, intestinal generalized hypo- or aperistalsis and short bowel. Along with the severe megacystis, malformations of the urinary tract with renal dysplasia (see this term), hydronephrosis, ureteral dilatation and hydroureter are frequently described. Undescended testis or bilateral streak gonads, cardiac anomalies, umbilical hernia or omphalocele have been reported in some cases.

Etiology of MMIHS is unknown but various hypotheses have been proposed to describe the pathogenesis including genetic, neurogenic, myogenic and hormonal origin. The 15q11.2 region might be associated with MMIHS.

Postnatally, MMIHS is mainly diagnosed by clinical presentation and supportive radiological and surgical findings. Histologically, vacuolar degeneration in the center of smooth muscle of the bowel and bladder has been described.

This disorder should not be mistaken for a milder and autosomal dominant disorder, called chronic idiopathic intestinal pseudo-obstruction, in which megacystis is also present, or for prune belly syndrome (see these terms).

Prenatal diagnosis of MMIHS is mostly based on fetal ultrasound, revealing enlarged urinary bladder and hydronephrosis. Recent reports have proposed prenatal magnetic resonance imaging (MRI) in combination with analysis of enzymatic changes to contribute to prenatal diagnosis of MMIHS. The enlarged bladder can be observed from the second trimester and polyhydramnios from the third.

MMIHS has been suggested to have an autosomal recessive inheritance pattern so genetic counseling remains difficult, to date.

There is no curative treatment for MMIHS. Various surgical interventions including gastrostomy, jejunostomy and vesicostomy have been reported and have been generally unsuccessful in most patients. Several multivisceral transplantations have also been reported. In the majority of patients total parenteral nutrition is required.

Survival in MMIHS seems to have improved, thanks to more specialized care, innovations in parenteral nutrition, and introduction of multivisceral transplantation. However, prognosis and life expectancy of this generally fatal disease remains poor. Death is mainly caused by sepsis, malnutrition or multiple organ failure.