Fetal megacystis as a prenatal challenge: megacystis–microcolon–intestinal hypoperistalsis syndrome in a male fetus

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The prenatal detection of megacystis is only the first step towards identifying the etiology and deciding on suitable treatment for this condition. Here we present a report highlighting the difficulties in the prenatal diagnosis of this severe fetal anomaly. A 28-year-old healthy primigravida was referred at 24 weeks' gestation to a tertiary hospital after an ultrasound scan at 18 weeks revealed megacystis and unilateral hydronephrosis in a male fetus with normal karyotype. On referral, a further ultrasound examination revealed a large bladder with a dilated posterior urethra (the ‘keyhole sign’) and normal wall thickness. Based on these findings, posterior urethral valves (PUV) syndrome was first suspected. Following weekly clinical and ultrasound surveillance, a progressive and unexpected increase in the amniotic fluid index (AFI) was observed in the third trimester, with polyhydramnios and grade IV hydronephrosis (Figures 1 and 2). These findings were suggestive of the rare megacystis–microcolon–intestinal hypoperistalsis syndrome (MMIHS). At 32 weeks' gestation, fetal magnetic resonance imaging (MRI) showed a dilated bladder measuring 135 × 111 × 86 mm that was compressing the abdominal organs, and severe bilateral hydronephrosis (21 mm right and 18 mm left); in addition, the stomach was clearly visible, but not the intestines (Figure 3). Vesicocentesis was performed for fetal urinalysis (sodium, potassium, calcium, phosphorus, creatinine, urea, total proteins and β2-microglobulin), and amniocentesis for evaluation of digestive enzymes (including γ-glutamyl transferase, alkaline phosphatase and biliary salts); findings from these tests were consistent with MMIHS. A Cesarean section was performed at 33 weeks, after spontaneous rupture of membranes. The neonate weighed 2950 g and had Apgar scores of 8 and 8 at 1 and 5 min, respectively. During the neonatal period the diagnosis was confirmed, and vesicostomy and total parenteral nutrition were needed. At 12 months, the infant had normal physical and neurological development, but still needed parenteral nutrition and vesicostomy. MMIHS is a rare congenital disease with fewer than 200 cases described in the literature, most of whom died in the first year of life1-4. It is characterized by a functional neonatal bowel obstruction with dilated small bowel, microcolon and non-obstructive urinary bladder distension. The etiology of the disease is unknown1-3. The prenatal sonographic features of MMIHS include megacystis, hydronephrosis, hydroureters, normal or decreased AFI in the second trimester, and polyhydramnios, intestinal and/or stomach dilatation in the third trimester1, 5-9. The fetal sex should also be considered, because MMIHS occurs 3–4 times more frequently in females2-5, 8, 9, although, as our case shows, the diagnosis should not be ruled out in male fetuses. The presence of oligohydramnios, progressive bladder wall thickening, hydronephrosis, echogenic kidneys and dilated posterior urethra are more suggestive of obstructive uropathy caused by a distal urethral obstruction such as PUV5, 9-11. For this reason, amniotic fluid analysis and fetal urinalysis are also helpful in the prenatal diagnosis of MMIHS6, 9, 12, as elevated digestive enzymes and high calcium levels, respectively, can be indicative of the disease6. Fetal MRI may also improve the diagnosis, especially when upper gastrointestinal tract distension (esophagus, stomach or small bowel) and microcolon are observed13. Despite the absence of pathognomonic findings of this rare syndrome, prenatal diagnosis is mandatory for optimal counseling and postnatal treatment.