REF Intraabdominal Fetal Echogenic Masses: A Practical Guide to Diagnosis and Management
Ann McNamara, MB, FFR (RCSI) and
Deborah Levine, MD
ENTERIC DUPLICATION CYST
CONGENITAL MESOBLASTIC NEPHROMA
The diagnosis of meconium peritonitis is made when scattered calcifications are seen throughout the peritoneum. The calcifications may be seen to line the liver (Fig 4). At times, only a focal calcification with shadowing is seen. Meconium peritonitis occurs when there is perforation of the bowel in utero, resulting in a sterile chemical peritonitis. In most cases, foreign-body giant cells and calcium deposits form within inflamed tissues, resulting in lesions that are echogenic at antenatal US. Eighty-six percent of fetuses with meconium peritonitis have intraabdominal calcifications at US (which occur at approximately 8 days after the perforation). These calcifications can be seen after 18 weeks gestation (7).
Causes of meconium peritonitis include ileal or jejunal atresia, volvulus, and microcolon. Cystic fibrosis is associated with meconium peritonitis, although the extent of association varies depending on the series examined (7,8).
DirkesK, Crombleholme TM, Craigo SD, et al. The natural history of meconium peritonitis diagnosed in utero. J Pediatr Surg1995; 30: 979–982.
FosterMA, Nyberg DA, Mahony BS, Mack LA, Marks WM, Raabe RD. Meconium peritonitis: prenatal sonographic findings and their clinical significance. Radiology1987; 165: 661–665.
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Associated abnormalities are often detected in fetuses with meconium peritonitis, particularly dilated bowel (27%–29%), fetal ascites (54%–57%), polyhydramnios (64%–71%), and meconium pseudocyst (Fig 5) (9). Meconium pseudo-cyst is seen as a well-defined hypoechoic mass surrounded by an echogenic calcified wall, indicating a contained perforation.
In the evaluation of the fetal abdomen for meconium peritonitis, the following should be documented: the site, size, and location of calcifications (including the scrotum and thorax) and the presence of dilated or echogenic bowel loops, meconium pseudocyst, ascites, and signs of hydrops fetalis.
When the calcifications are isolated, there generally is a favorable neonatal outcome and intervention is not necessary (Fig 4). In the series of Dirkes et al (7), all five fetuses with isolated calcifications had a normal outcome at postnatal follow-up. These cases are thought to represent perforation of bowel that spontaneously heals in utero. Therefore, in the absence of other findings, isolated calcifications can be followed sonographically during pregnancy. Parental cystic fibrosis gene carrier status can be assessed. In this assessment, parental blood is tested for the 25 most common alleles associated with cystic fibrosis, allowing detection of 90%–97% of cystic fibrosis cases. However, it has been shown that peritoneal calcifications have a lower association with cystic fibrosis than had been previously thought (8). After birth, plain radiography of the abdomen is performed, frequently followed by upper and lower gastrointestinal tract barium studies to assess for occult perforation. If results of these studies are normal and the neonate has passed meconium, no further follow-up is needed.
When peritoneal calcifications are seen in conjunction with other findings, the outcome is more guarded (7). Closer follow-up is warranted. Post-natal imaging commonly demonstrates obstruction with or without perforation, and surgery is often indicated.
Liver Calcifications and Calcified Liver Lesions
Calcifications in the fetal liver are a relatively common finding, identified at 1 in every 1,750 second-trimester US examinations (10). The site, size, and distribution of the lesions are major factors in determining further management. The presence of an associated liver, abdominal, or retroperitoneal mass as well as the association with ascites are important considerations.
If the liver calcifications are single, no other fetal morphologic abnormalities are detected, and infectious screening tests are negative, then the prognosis is promising. Follow-up sonography typically shows stability or regression of the finding, and no further work-up is required.
Punctate echogenic lesions on the surface of the liver usually represent peritoneal calcifications, the commonest source of which is meconium peritonitis (Fig 5). Isolated subcapsular calcifications also can be due to emboli from the portal or hepatic veins (11).
Calcifications in the liver can be single or multiple (Fig 6). In the majority of cases in which isolated hepatic calcific deposits are detected, no underlying abnormality is found. Most studies document that screening tests for the infections associated with calcifications in the liver—such as cytomegalovirus infection, toxoplasmosis, rubella, syphilis, and herpes simplex—are negative, and the outcome is almost always favorable if no other abnormality is detected (10–12). A vascular etiology for these lesions has been postulated but not proved (12). The development of ascites is associated with congenital viral infection (13).
Calcified liver masses are suspicious for malignancy. These tumors are very rare, the most likely being hepatoblastoma (a heterogeneous mass with coarse calcifications and an osseous matrix) and metastatic neuroblastoma (a poorly differentiated neural crest cell tumor, most commonly originating in the adrenal gland).
Hemangioma is a benign tumor characterized by increased turnover of endothelium, mast cells, macrophages, and fibroblasts. It is the commonest tumor of infancy, occurring most often in the liver, lung, and gastrointestinal tract (Fig 8). Although it is the commonest vascular tumor, antenatal detection is uncommon. Hemangioma is classically a well-defined echogenic liver lesion. It tends to appear avascular at color Doppler sonography and is more likely to exhibit calcification than hamartoma. Hemangiomas up to 12 cm have been described antenatally (19). With lesions of this size, significant morbidity has been reported. Complications are related to congestive cardiac failure, thrombocytopenia, anemia, and intraabdominal hemorrhage as a result of rupture of the tumor. Maternal steroids and interferon alpha-2a have been used to treat these lesions medically with varying success (9). When these methods fail, surgery may be required postnatally. Spontaneous regression of hemangioma has been documented.
Enteric Duplication Cysts
Enteric duplication cysts are structures in immediate contact with the alimentary tract, made up of a two-layer smooth muscle wall and an internal epithelium of a respiratory or intestinal type. They are associated with additional abnormalities in one-third of cases, particularly those of the spine and gastrointestinal tract (20). These cysts are typically anechoic but can manifest as an echogenic abdominal mass (Fig 9). The thick wall that duplication cysts possess can make differentiation from mesenteric cysts difficult (20). These cysts may or may not communicate with the lumen of the gastrointestinal tract. They are classified as cystic or tubular. The tubular type communicate with the bowel more commonly and are less likely to be identified at sonography.
Most gastric duplications are cystic and of the noncommunicating type. They are found on the greater curve of the stomach near the pylorus. The differential diagnosis of gastric duplication includes retroperitoneal tumor (neuroblastoma) and teratoma of the stomach.
Forty percent of duplication cysts involve the ileum (20). The colon and rectum can also be affected. The most common complication is bowel obstruction. Hemorrhage and perforation have also been described. Surgery is therefore recommended in most cases. If an enteric duplication is suspected, examination should be directed toward the identification of communication with the remainder of the gastrointestinal tract, dilated bowel loops, and/or evidence of perforation. Spinal malformations are associated with foregut duplications; thus, careful evaluation of the spine should be performed. Follow-up examinations should be directed to documenting change in size, development of calcifications, and the presence of bowel obstruction.
Neuroblastoma is the most common neoplasm of the adrenal gland (Fig 10). It is usually identified for the first time in the third trimester at a mean gestational age of 36 weeks. Associated malformations are unusual. Neuroblastoma is characteristically a heterogeneous solid mass with cystic components that displaces the adjacent kidney inferiorly and laterally. It can metastasize to the liver. Spontaneous regression occurs in up to 40% of cases. Peripheral calcification may persist.
Subdiaphragmatic Extra-lobar Pulmonary Sequestration
Approximately 10%–15% of extralobar pulmonary sequestrations occur below the diaphragm, where there is a 4:1 left-sided predominance (9). In contrast to this, neuroblastomas are more commonly right sided. In addition, sequestrations are generally appreciated earlier in the pregnancy, in the second trimester, and are more echogenic than neuroblastomas (Fig 11). If a feeding vessel can be seen arising from the thoracic aorta and extending below the diaphragm to the mass, this strongly favors the diagnosis (9).
Congenital Mesoblastic Nephroma In utero, it is seen as a large solid vascular mass (Fig 12). Owing to arteriovenous shunting, heart failure and polyhydramnios are common. Mesoblastic nephroma is benign, and postnatal nephrectomy is curative (22).
Color Doppler image shows blood supply from the ipsilateral renal artery. At surgery, a mesoblastic
Work-up of Adrenal Region Lesions
The following approach to assessment of lesions in the adrenal region is suggested: First, determine if the mass is of renal or adrenal origin. At times, this is not possible to determine. When a mass identified during a routine fetal survey (18–22 weeks gestation) is uniform and left sided, consider subdiaphragmatic extrapulmonary sequestration the most likely cause. If the mass is uniform with a central cystic portion, right sided, or bilateral, then adrenal hemorrhage is at the top of the differential diagnosis list, particularly if follow-up shows rapid resolution. In both cases, management is expectant.
If a highly vascular mass is identified later in pregnancy and is not clearly separate from the kidney, consider mesoblastic nephroma. Most pregnancies with mesoblastic nephroma will deliver prior to 38 weeks gestation. Postnatal nephrectomy (or partial nephrectomy) is curative. If a mass identified at this stage of gestation is right sided with cystic spaces, consider neuroblastoma and assess carefully for liver metastases. Close expectant management should be advised with resection in the neonatal period.