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Not Your Typical Renal Cyst

Computed tomography (venous phase) of the abdomen and pelvis shows a large thick-walled, centrally hypodense, cystic mass (arrow) in the left portion of the horseshoe kidney.

Computed tomography (venous phase) of the abdomen and pelvis shows a large thick-walled, centrally hypodense, cystic mass (arrow) in the left portion of the horseshoe kidney.

A 32-year-old man with no significant past medical or family history presented to his primary care physician with lower back and abdominal pain. Renal function tests and urinalysis were unremarkable. Computed tomography scan demonstrated a mixed cystic solid renal lesion with focal wall thickening and contrast enhancement within the left portion of a horseshoe kidney.

Assessment

The patient was referred to our institution. Follow-up imaging showed that while the cyst was stable in size (5.8 × 5.9 cm), the peripheral enhancement and calcifications (Figure 1) raised concerns for cystic renal cell carcinoma (Bosniak classification of renal cysts category IV). There was no evidence of metastases. The patient underwent a partial nephrectomy.

Diagnosis

Pathology revealed a 5.8-cm well-differentiated neuroendocrine carcinoma with extensive necrosis, perineural invasion, and extension into perinephritic tissue (Figure 2). Surgical margins were negative. Immunohistochemical stains showed that the tumor exhibited a high mitotic count (20 mitoses per 10 high power fields by phosphohistone H3 stain) and elevated Ki-67 labeling index (20%). These findings are consistent with an aggressive histology.

Management

The patient was followed closely postoperatively. He did not report symptoms of carcinoid syndrome (eg, pain, flushing, diarrhea), and his Eastern Cooperative Oncology Group performance status was excellent (grade 0). However, 13 months after surgery, computed tomography of the abdomen and pelvis showed a possible sclerotic density within the medial left iliac wing. Imaging 30 months after surgery confirmed several sclerotic bone lesions consistent with metastases. An octreotide scan was positive for bone uptake and possible uptake in the surgical bed. The patient began receiving denosumab to prevent bone loss and lanreotide injections, a synthetic somatostatin analogue used to treat neuroendocrine tumors.

One year later, multiple enhancing liver lesions were found and biopsy confirmed metastatic neuroendocrine carcinoma. It has now been more than 4 years since surgery, and he is also taking sunitinib, a targeted tyrosine kinase inhibitor that has been US Food and Drug Administration approved for gastrointestinal stromal tumors, renal cell carcinomas, and pancreatic neuroendocrine tumors. The patient has tolerated the medication well, with minor bloating and occasional nausea, but his prognosis remains guarded because of extensive metastatic disease.

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-Yaolin Zhou, MD, Shi Wei, MD, PhD

This article originally appeared in the October 2017 issue of The American Journal of Medicine.

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