What you need to know about fetal abdominal masses

Key Points

With routine antenatal ultrasound and advances in ultrasound technology, fetal intra-abdominal cystic masses are recognized more often and are better characterized than in the past. These lesions are usually first suspected when evaluation of the fetal abdomen results in the identification of a cystic mass, independent of the expected sonolucent areas of the bladder and stomach. They are often detected at the time of a patient's anatomical survey at about 18 to 20 weeks' gestational age.

Such diagnoses can be unsettling for the patient, as well as for the physician who generally does not encounter such findings in daily practice.

The key to differential diagnosis hinges on the suspected system from which the mass originates as well as the fetal gender. The origin of the cysts can be divided into potential etiologies: reproductive, bowel, mesentery, or other organs. The urinary system is the most common site of abdominal masses; however, we will not consider the kidneys, ureter, and bladder in this review.

Management is conservative and depends on mass size, symptoms, and presence of complications. Masses greater than 4 cm to 5 cm are associated with a risk of torsion approaching 50% to 78% and typically warrant postnatal surgical resection.^3-5 Neonatal cyst aspiration is generally not recommended because of recurrence risk and the need to ensure that malignancy is not present.³ Otherwise, spontaneous regression is expected for a simple ovarian cyst. If bleeding is suspected within a cyst, excision is usually considered despite size because of its high association with torsion. Complex-appearing cysts (ie, those with septae, nodules, etc) usually undergo surgical removal because of malignant potential.

The gastrointestinal system

Stomach

Stomach size varies with gestational age, filling and emptying during the course of an ultrasound examination. If this does not occur, a cause should be sought. Stomach dilation occurs in proximal obstruction, from duodenal or jejunal intestinal atresia. The etiology may be neurologic or lie within the musculature.

An enlarged stomach can rarely be caused by gastric outlet obstruction other than that associated with duodenal atresia. Failure of recanalization of the gastric lumen during development can lead to pyloric stenosis, with an occurrence of about 1 to 5 per 1,000 births.^2,6,7 Although this diagnosis is usually made after birth, there have been case reports of the detection of pyloric stenosis in the antenatal period.⁸ However, problems with gastric lumen recanalization may produce a membranous antral web leading to pyloric atresia. The latter is far more rare than pyloric stenosis and occurs is about 1 in 1 million births.^2,6,7 Pyloric atresia can be associated with a dermatologic condition called epidermolysis bullosa. In either case, although rarely seen antenatally, a dilated stomach with polyhydramnios and hyperperistalsis in the pyloric antral area can be seen.⁸ Long-term outcome depends on the presence and type of other anomalies, and treatment involves decompression and surgical correction in the postnatal period. Rarely, a congenital duplication of the stomach or a duplication cyst can occur. If present, this can be associated with duplication of other gastrointestinal organs.

Megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS) is a rare constellation of ultrasound findings that includes a dilated stomach. This syndrome results from impaired neuromuscular function of the stomach and bowel. MMIHS is an autosomal recessive condition occurring in females more than males that is usually fatal in the first year of life.⁹ Ultrasound findings include a large, thin-walled bladder and bilateral hydronephrosis, occasionally with visibly dilated ureters.^10,11 Normal or increased amniotic fluid volume can be appreciated, likely because of microcolon.

Echogenic structures may be seen within the lumen of the stomach in about 1 in 300 second-trimester ultrasounds.¹² These usually result from the fetus swallowing bloody amniotic fluid. A maternal history of genetic amniocentesis is often seen with this finding.