Uretheral invagination of multilocular cystic nephroma; a case report of a new pathologic variant.

Background: The multilocular cystic nephroma (MLCN) is a unilateral cystic neoplasm of the kidney exhibiting benign biological behavior. The etiology and histopathogenesis of the disease is controversial (dysplastic/hamartomous/neoplastic). MLCNs show bimodal age distribution, with peak incidence occurring at 2-4 years of age and between the fourth and sixth decades. The male to female ratio in patients aged below 4 years is 3:1, which reverses to 1:8 between the fourth and sixth decades.
Patients and Methods: A 59-year-old female patient presented with left flank pain and abdominal pain. Ultrasound (US) revealed 220×109×82 mm multiple septated hyperechoic kidney cysts with a semi-solid appearance. MRI showed a 245×119×98 mm multilocular cystic renal mass in the left kidney with hypointense appearance in T1-weighted images and hyperintense in T2-weighted images, and multicystic appearance in ureter projection, the largest portion measuring 17 mm in diameter. Radical nephrectomy was planned with the pre-diagnosis of multilocular cystic nephroma or multicystic renal cell carcinoma.
Results: The patient underwent transperitoneal radical nephroureterectomy. The immunohistopathological examination revealed MLCN with ureteral invagination.
Conclusion: The etiology, pathogenesis, and genetic basis of multilocular cystic nephroma are currently unknown. This tumor is confused with cystic partially differentiated nephroblastoma and cystic Wilms tumor in childhood, and multilocular cystic renal cell carcinoma, clear cell papillary renal cell carcinoma, and tubulocystic carcinoma in adults. The association of this tumor with pleuropulmonary blastoma in children exhibits genetic inheritance. US control is particularly recommended in siblings of these children. Albeit rare, the disease can occur as a bilateral synchronous or metachronous lesion. There are four reports of cases with recurrence in the literature. The laparoscopic partial nephrectomy is the recommended treatment method in patients with sufficient renal reserve that are found to be free of malignancy in the frozen section examination. The symptoms of hematuria and flank pain can be associated with invagination of the cysts into the pelvis and intrarenal rupture of the cysts. The invagination of cysts into the pelvis has been previously described. The authors consider that this was the first case of MLCN in the literature exhibiting invagination into the ureter.