Applied Radiology

CASE SUMMARY:

A 34-year-old female (gravida 5, term 2, para 2, abortion 2, living 2) presented to the ultrasound lab as measuring large for gestational dates. She was normotensive and asymptomatic. Her prenatal course had been unremarkable, and she reported no incidences of bleeding or pain. She had no personal or family history of birth defects. Images from a routine obstetrical ultrasound are illustrated in figures 1-4. Following the ultrasound, a fetal karyotype demonstrated a normal 46 XY male. Two weeks later, she delivered a still-born male fetus. Autopsy results confirmed the presence of an 8-cm unencapsulated neoplasm replacing the normal right kidney and extending into the lateral abdominal wall. The mass compressed the liver and inferior vena cava. There was generalized body wall edema. Microscopic examination revealed an infiltrative neoplasm composed of spindle cells with fine chromatin along with residual renal parenchyma and areas of necrosis and dystrophic calcifications.

FIGURE 1. Transverse image of the fetal abdomen demonstrating a large 5-cm cystic and solid mass in the right abdomen. Abdominal ascites is present.

FIGURE 2. Ultrasound image of the fetal calvarium displays skin thickening consistent with anasarca and hydrops.

FIGURE 3. Sonogram of the fetal scrotum shows large bilateral hydroceles.

FIGURE 4. Ultrasound image shows a large pocket of amniotic fluid. The amniotic fluid index was calculated to be 25 cm, indicative of polyhydramnios.

DIAGNOSIS:

Congenital mesoblastic nephroma in association with hydrops fetalis

IMAGING FINDINGS:

The patient was scanned using a Toshiba SSH 140A and a 5 MHz transducer. Obstetrical ultrasound revealed a large, complex cystic mass measuring 8.5 × 6.3 × 6.1 cm within the upper fetal abdomen centered just to the right of midline and extending into the lateral abdominal wall. The mass distorted the fetal abdomen and the thoracic cavity appeared compressed. Bilateral hydroceles, ascites, and anasarca were noted consistent with fetal hydrops. The amniotic fluid index (AFI) was 25 cm or >97.5 percentile consistent with polyhydramnios. The biparietal diameter and the femur length were compatible with a 27-week gestation. The abdominal circumference measured >95th percentile for a 27-week gestation. The placenta was slightly edematous, measuring 4.6 cm in thickness. The right kidney could not be identified. Differential diagnosis considerations included multidysplastic kidney, congenital mesoblastic nephroma, and Wilm's tumor.

DISCUSSION:

Mesoblastic nephroma is the most common neonatal renal neoplasm. ¹ Mesoblastic nephroma is usually discovered within the first few months of life, however, it may be diagnosed by obstetrical sonography as a complex renal mass. ² Occasionally the pregnancy may be complicated by hydramnios or dystocia, but usually the prepartum history is unremarkable. ² Mesoblastic nephroma may demonstrate gross cystic changes involving the junction of the tumor and the normal kidney, thus mimicking a multilocular cystic nephroma. ³ Congenital mesoblastic nephromas are usually a benign disease, but in association with hydrops fetalis can result in fetal death as was the situation in this case report. After a review of the English literature, we could find only one other case of fetal hydrops in association with congenital mesoblastic nephroma that was diagnosed prenatally. ⁴ There were two other cases of fetal congenitalmesoblastic nephroma associated with hydrops fetalis; however, these were both diagnosed following autopsy. ^5,6

Most renal anomalies result in oligohydramnios and, therefore, a renal anomaly in association with polyhydramnios should be concern for a mesoblastic nephroma. The etiology of the polyhydramnios is uncertain; however, some observations have included a relationship to gastrointestinal compression by the tumor or that the tumor will increase fetal urine production. ⁷ The outline of a mesoblastic nephroma may be difficult to ascertain because it is not always encapsulated in contrast to a Wilm's tumor. ⁸

It is important that this anomaly is diagnosed prenatally in order to ensure proper obstetrical management to avoid such occurrences as premature birth and dystocia.

Prepared by Crosby L. Gernon, MD, Chairman of Ultrasonography, and Bob Alston, BS, RDMS, RVT, Chief Sonographer, Department of Ultrasound, at Sabetha Community Hospital of Sabetha, KS.