Paraspinal Extrarenal Wilms Tumor Case Report and Review of Literature.

Introduction: Extrarenal Wilms tumors (ERWTs) (i.e., nephroblastoma) are exceptionally rare tumors that have only been reported approximately 100 times in the literature. These tumors necessitate histology (rather than imaging) for proper identification, often resulting in a postoperative diagnosis. Case Presentation: At 20 weeks of gestation, a female fetus was diagnosed with a subcutaneous lumbosacral mass by prenatal ultrasound (US). Days after birth, the mass was resected and pathologically determined to be an ERWT. Specifically, the excised mass had a triphasic histologic pattern, including blastemal, stromal, and primitive epithelial components. Centrally, the lesion demonstrated cystic and pseudopapillary architectural features, while peripherally, the lesion was more solid with the morphologic appearance of Wilms tumor (WT). This case is unique due to (1) the unusual lumbosacral location, (2) the presence of normal bilateral kidneys on US, and (3) the detection of the mass on in utero imaging studies. Literature Review: Including our report, ERWT has been reported 16 times in the (para)spinal/vertebral region and range from T9 to the coccyx. Most patients initially receive surgery (gross total resection, if feasible) followed by chemotherapy (vincristine and dactinomycin) and radiation depending on final pathology and additional case considerations. Discussion: Due to the rarity of ERWTs, there is no standardized treatment. Complete excision with adjuvant chemotherapy (vincristine and dactinomycin) is most often suggested as a best/most appropriate approach to treatment, with the addition of radiotherapy for recurrence and/or metastasis. Conclusion: This case report and literature review highlights the necessity of considering ERWT as a potential diagnosis when faced with a patient who has a lumbosacral paraspinal/spinal mass, even if other clinicoradiographic features typical of WT are not identified. We also call to light the need for a standardized treatment regimen for ERWT.