Recurrent Congenital Mesoblastic Nephroma: A Case Report

Congenital mesoblastic nephroma (CMN) is the most common tumor of kidney in early infancy. We present here a case of antenatally detected right renal mass that was excised and reported cellular CMN. He developed recurrence while on adjuvant chemotherapy. We emphasize that the management of cellular CMN, especially adjunct chemotherapy, has not been standardized yet.


INTRODUCTION
Congenital mesoblastic nephroma (CMN) is mostly a benign tumor of kidney, with nephroureterectomy as a standard of care and usually excellent prognosis. The cellular or atypical CMN is potentially aggressive variant and is known for local recurrence and even distant metastasis. With documented chemosensitivity of CMN, we propose the pendulum should be swung in favor of sarcoma-based chemotherapy.

CASE REPORT
The antenatal scan of a baby at 32 weeks gestation detected right renal mass arising from upper pole with polypoidal and peripheral cystic components (Fig.1). It was associated with retroperitoneal perirenal collection? hemorrhagic. The post-natal computed tomography performed at 3 weeks of age revealed a 6.5 x 5.2 x 4.1 cm right renal mass with solid and cystic components and associated localized peri-renal collection (Fig.2

CASE REPORT
He received 13 cycles of Actinomycin-D and vincristine based chemotherapy, starting from 40th postoperative day. At the age of 4.5 months (while on chemotherapy), he developed recurrence that grew to larger than original tumor in coming 6 weeks.
CECT of abdomen showed a large complex heterogenous, predominantly cystic mass in right renal fossa, with multiple hemorrhagic areas ( Fig.3). At 6 months age, he was first seen at our center. Exploration revealed a large friable mass infiltrating adrenal gland. The tumor got ruptured intraoperatively; R2 resection was done. HPE showed tumor composed of round by spindled out cells present in sheet, entrapping adrenal gland, clear to eosinophilic cytoplasm, showing brisk mitosis and cystic degeneration, suggestive of cellular CMN (Fig.4).  He received whole abdomen radiation 10.8 Gy over 6 fractions in view of intra-op tumor rupture and 6 cycles of adjuvant chemotherapy (Ifosfamide, Carboplatin and Etoposide-ICE). He has been in close follow up and is disease-free for last 10 months.

DISCUSSION
CMN accounts for 3-10% of childhood renal tumors [1] and commonly present in less than 2 months of age. Two main variants are recognized on histology, classical and cellular variants. The cellular or atypical CMN is known for local recurrence and even distant metastasis. The genetic aberrations mentioned in CMN include somatic trisomy 11 and t(12;15)(p13;q25), resulting in a fusion of ETV6 and NTRK3. [2,3] Shared histopathology and translocation gene fusion results support the concept of cellular CMN as the renal form of infantile fibrosarcoma (IFS), while classic CMN is equivalent to infantile fibromatosis. [4] The antenatal diagnosis of CMN and its opponent renal tumors like Wilm's tumor is difficult to conclusively confirm, as many masses show solid and cystic components and even polyhydramnios. [ The chemosensitivity of CMN tumor is well documented as evidence by reduction in size or necrosis post neoadjuvant chemotherapy such as Actinomycin-D and vincristine (AV) regimen. [6,9] But the need for neo-adjuvant chemotherapy in CMN may only be indicated in case of large mass or risk of tumor rupture intra-operatively. To conclude, AV therapy used for Wilms tumor is not an ideal chemotherapy for cellular CMN and chemotherapy used for sarcomas should be administered to infants with cellular CMN.

Consent:
Authors declared that they have taken informed written consent, for publication of this report along with clinical photographs/material, from the legal guardian of the patient with an under-standing that every effort will be made to conceal the identity of the patient however it cannot be guaranteed.