Contributed by Henry Armah, MD, and Anil Parwani, MD, PhD
The patient is a 39-year-old woman who had a left kidney tumor incidentally discovered during CT scan as part of a diagnostic workup for colonic diverticulosis. She had no personal or family history of significance, including no personal or family history of tuberous sclerosis complex (TSC), lymphangioleiomyomatosis, renal cyst, renal malignancy, or estrogen hormonal therapy. The CT scan demonstrated a 2.5-cm complex cystic mass in the upper pole of the left kidney with a 1-cm enhancing nodule in its wall, radiologically worrisome for cystic renal cell carcinoma. In view of this concern of malignancy, the patient elected to undergo laparoscopic left partial nephrectomy for definitive surgical treatment. The entire tumor was surgically resected with an excellent margin of 5-mm of normal parenchyma surrounding the entire cyst wall, and the tumor was confined to the kidney. She is alive with no evidence of recurrence or metastatic disease, 24 months postoperatively, and subsequent clinical follow-up with interval abdominal imaging studies is planned.
Grossly, the tumor was well demarcated and partially cystic, with the largest cyst measuring up to 1.1-cm. Sectioning of the tumor revealed part of the cyst wall contained a single 1-cm mural nodule with homogenous tan cut surface. The entire tumor was submitted for histological examination.
The histological examination revealed three components of the tumor. The first component was cystic or multicystic spaces lined by epithelium, which ranged from flat to cuboidal to columnar. Whilst the cuboidal to columnar cells had unremarkable clear cytoplasm, the flat cells had abundant eosinophilic cytoplasm with nuclei that often protruded into the lumen, resulting in a hobnailed appearance [image 1]. The second component was a subepithelial "cambiumlike" condensation of small stromal cells with indistinct cytoplasm immediately subjacent to the cyst epithelium. This subepithelial stroma showed prominent capillary vasculature (reminiscent of endometrial or mullerian-like stroma) and prominent lymphoplasmacytic infiltrate [image 2]. The third component was a thick exterior wall of plump smooth muscle cells with focally clear cytoplasm arranged in poorly formed fascicles, often appearing to emanate from irregular and tortuous blood vessels [image 3]. The third component was exterior to the subepithelial stroma and was typical of myomatous or muscle- predominant predominant AML. Additionally, noncystic native renal tubules were observed entrapped within this exterior muscular wall [image 4].
HMB45 [image 5] and Melan-A labeling was patchy in the exterior muscle-predominant AML component, but were most intense and concentrated in the compact subepithelial cellular stroma. Conversely, smooth muscle actin [image 6] and desmin labeling was most intense and concentrated in the exterior muscle-predominant AML component, but were patchy in the compact subepithelial cellular stroma. Similarly, the compact subepithelial cellular stroma showed strong and diffuse nuclear labeling for estrogen receptor (ER) [image 7] and progesterone receptor (PR) [image 8], along with strong and diffuse cytoplasmic labeling for CD10 [image 9], but labeling for ER [image 7], PR [image 8], and CD10 [image 9] were patchy in the exterior muscle-predominant AML component. However, vimentin [image 10] showed strong and diffuse cytoplasmic labeling of all 3 components equally. The cyst lining was positive for epithelial markers (pancytokeratin [image 11], AE1-AE3, and CK7), but negative for melanocytic (HMB-45 [image 5] and Melan-A), muscular (smooth muscle actin [image 6] and desmin), and hormonal (ER [image 7] and PR [image 8]) markers. The tumor showed low proliferative index with Ki67 labeling less than 1% of neoplastic cells [image 12]. Additionally, RCC marker antigen, inhibin, WT-1, c-kit (CD117), S-100 protein, and CK20 did not label any of the 3 components of the tumor (not shown). Except for patchy labeling of blood vessels, CD34 (endothelial markers) did not label any of the 3 components of the tumor (not shown).