Leiomyosarcoma is a malignant tumor of smooth muscle component of soft tissue. It is essentially a tumor of adults or elderly but cases have also been reported in children [2
]. Apart from the uterus, soft tissue leiomyosarcoma commonly occurs in the retroperitoneum, and also arises from the blood vessels. Leiomyosarcomas of nonperitoneal soft tissue sites usually involve the lower extremity but they can occur in the head and neck region also [3
Primary leiomyosarcomas are rare in the kidney and represent 1%-2% of all malignant renal tumors [1
]. They appear to arise from renal capsule or smooth muscle tissue of the vessels or renal pelvic wall. The mean age at presentation is 50–60 years with a female preponderance. Grossly, the tumors look like leiomyomas with a well-circumscribed margin and whorled cut surface. The malignant counterpart, however, appears fleshy and has areas of necrosis, haemorrhage, and cystic degeneration [4
]. Leiomyosarcomas rarely metastasize to the kidney. In case of metastasis, they appear as intraparenchymal lesion or as a microscopic diagnosis. Bulky tumors that replace and invade the renal tissue are typical of renal leiomyosarcoma as seen in this case.
Microscopically, leiomyosarcomas show characteristics of smooth muscle tumor with alternating fascicles of spindle shaped cells. The cells have blunt ended, nontapering nuclei and eosinophilic cytoplasm [5
]. Indicators of malignancy are necrosis, nuclear pleomorphism, and more than rare mitotic figures [6
]. Grignon et al. [6
] have recommended that large smooth muscle tumors should be treated with high suspicion unless proved otherwise. Focal myxoid change has also been reported [5
Epithelioid angiomyolipoma, a variant of angiomyolipoma, can be mistaken for a leiomyosarcoma. Occasionally, the smooth muscle cells are epithelioid and exhibit nuclear atypia. They are negative for epithelial markers [7
] but positive for smooth muscle and melanocytic markers. Another important differential diagnosis is sarcomatoid variant of renal cell carcinoma. Morphologically, this tumor lacks the alternating fascicles, is more pleomorphic, and usually has foci of typical renal cell carcinoma. Absence of smooth muscle markers with cytokeratin positivity is supportive of a diagnosis of carcinoma [5
]. Primary monophasic synovial sarcoma of the kidney also shows monophasic spindle cells. The spindle cells are plump with irregular cell borders. They tend to grow in sheets and usually have entrapped renal tubules within them in the form of cysts. However, these tumors show positivity for Bcl-2 [8
]. Fibrosarcoma and malignant peripheral nerve sheath tumor are other differential diagnoses to be considered.
The most common presenting sign is an abdominal mass with or without pain and haematuria similar to renal cell carcinoma [1
]. Leiomyosarcomas, metastasizing to lungs, liver small intestine, and colon have been discussed but renal leiomyosarcomas with adherence of colonic segments only without any microscopic evidence of metastasis are rare. Sonography demonstrates multinodular masses sometimes defining the origin. Computed tomography imaging shows multinodular low-density areas with high-density septum- like structures [9
Radical nephrectomy is the treatment of choice for renal leiomyosarcoma [1
]. However, chemotherapy and radiotherapy are also recommended considering the aggressive behavior of the neoplasm. Despite resection, the tumor shows an unfavourable prognosis, metastasizing to lungs, liver and colon.