Congenital mesoblastic nephroma: a case report.

Congenital mesoblastic nephroma (CMN) is a rare renal tumor. It can be detected antenatally especially with judicious use of ultrasonography.A premature female neonate 28 weeks' gestation, complicated by polyhydramnios, was born to a 28-year-old woman. An abdominal mass was detected antenatally. At the end of the first week of life, the newborn had hypertension that was controlled by hydralazine. Ultrasonography and CT scan showed a right-sided renal heterogeneous solid mass. Right nephrectomy was performed and the histology showed CMN.

INTRODUCTION

Neonatal tumors are rare; however, congenital mesoblastic nephroma (CMN) is the most common neonatal renal tumor.12 The association between CMN and polyhyramnios, hypertension and prematurity has been well described; and although CMN is a benign tumor, it could behave aggressively, resulting in catastrophic complications.3–5

We report a 28-week preterm newborn with a maternal history of polyhyramnios, hypertension in neonatal period and a right-sided renal mass which was confirmed as CMN by histopathology.

CASE REPORT

A premature infant girl was born to a 28-year-old healthy woman (G3, P2) after 28 weeks of gestation. The mother was admitted at 26 weeks gestation because of respiratory difficulty. Ultrasonography showed polyhydramnios. It required therapeutic amniocentesis, about 2000 ml of amniotic fluid was drained. Ultrasonography showed a solid mass involving the right kidney. Two weeks later, the mother developed early labor pain and delivered vaginally.

The infant was born apneic, cyanotic, and bradycardic, and was resuscitated successfully. On admission to the NICU, vital signs were stable. She required mechanical ventilation and surfactant therapy. Physical examination on the first day of life showed a palpable right flank mass occupying almost the whole of the right side of the abdomen. At the end of the first week of life, she developed hypertension that wascontrolled by hydralazine.4 Serum creatinine, blood urea nitrogen and serum electrolytes were within normal limits. Serum renin and aldosterone levels were not measured.

Abdominal ultrasonography showed a 55mm × 40mm heterogeneous solid mass involving the right kidney area. CT scan confirmed a large hypodense mass with heterogeneous enhancement arising from the right kidney with cortical enhancement (Figure 1).

Figure 1

CT Scan of right kidney

After stabilizing the cardio-respiratory status, the newborn underwent an exploration laporatomy at the age of 4 weeks. Right nephrectomy was performed. Gross pathological examination showed a solid renal tumor weighing 50 grams and measuring 4 × 5 × 4.5 cm. No necrosis or hemorrhage was identified. Microscopy revealed a moderately cellular spindle cell neoplasm infiltrating adjoining renal parenchyma, perirenal fat and renal sinus. However, the renal pelvis and calyces and the suprarenal gland were not infiltrated, no vascular invasion was seen. There was a moderate nuclear pleomorphism and mild to moderate mitotic activity.

The neoplastic cells showed positive immunoreactivity for vimentin. There was no reactivity for desmin, actin, keratin or S-100 protein. The kidney had an embryonic appearance (Figure 2), which could be described as mesoblastic nephroma, mixed classic and cellular variant.

Figure 2

Microscopic picture of CMN

DISCUSSION

Congenital mesoblastic nephroma is the commonest neonatal renal tumor; which mostly presents as a palpable abdominal mass.12 The differential diagnosis of a neonatal abdominal mass includes CMN, Wilm's tumor, neuroblastoma, rhabdoid tumor, clear cell sarcoma of the kidney, and renal cell carcinoma.12 Although CMN is usually a benign tumor it can be aggressive in behavior.3 Thus, total nephrectomy is curative.45 In this case, the abdominal mass was detected antenatally by ultrasonography. An increasing number of cases have been diagnosed antenatally especially with the widespread use of antenatal ultrasonography.67

There are two main subtypes of CMN. The classic (typical) type, which is the more common, is of a benign nature and has a better prognosis. The second, the cellular (atypical) variant, is less common and runs an unpredictable course.6 Nevertheless, a mixed type, as in our case, has been reported.7

In our report, the mother had polyhydramnios, believed to be due to fetal polyurea, that required therapeutic amniocentesis. Polyhydramnios, with or without hydrops fetalis, and/or preterm labor are associated with CMN.7

Some CMNs are associated with paraneoplastic syndromes such as hypertension (due to hyperreninemia) and hypercalcemia (due to prostaglandin secretion from the tumor cells).6–8 Our patient developed hypertension at the end of the first week of life and was controlled by hydralazine. Serum creatinine, blood urea nitrogen, and serum electrolytes were within normal limits. Renin and aldosterone levels were not measured.

This report is of a preterm infant girl, of 28-week gestation with CMN of mixed histology (classic and atypical), polyhydramnios and hypertension. The right-sided abdominal mass was detected antenatally by ultrasonography, after which the patient underwent a total nephrectomy. The diagnosis of CMN was made by histopathology. Based on the review of literature and the author's knowledge, this is the youngest reported patient with CMN of mixed histology and hypertension.