Abstract
A case of benign mixed tumor of the soft tissue in a 64-year-old Japanese male is presented. He noticed a painless, elastic hard mass sized 3 cm in the right knee, which gradually grew larger and harder in the last 5 years. Magnetic resonance imaging demonstrated a mass lesion embedded in the subcutaneous tissue with low and high signal intensity at T1- and T2-weighted images, respectively. Tl-201 scintigraphy showed an early uptake of Tl-201 within the lesion at 10 minutes after injection, which was slightly decreased but still continued at 2 hours later. The patient underwent a resection of tumor, and the pathological diagnosis was a benign mixed tumor of soft tissue without high vascularity, characterized by histological features similar to pleomorphic adenomas in the salivary glands. Immunohistochemical study proved expression of Na+/K+-ATPase of tumor cells. Overexpression of Na+/K+-ATPase of the tumor might be responsible for the early uptake of Tl-201, and poor vascular structure in this tumor might lead to continuous accumulation. The Tl-201 scintigraphic features of mixed tumor of soft tissue are assessed to resemble those of malignant soft tissue tumors.
Highlights
Mixed tumors can occur in soft tissue as well as in the skin and soft palate [1,2], only 18 cases have been described to be primary in soft tissue [3,4]
We present a case of benign mixed tumor arising in the subcutis, which demonstrated an early uptake of thallium-201 chloride (Tl-201) with slightly decreased accumulation in the delayed scan
Thallium-201 chloride (Tl-201) scintigraphy showed an uptake of Tl-201 into the mass at early scan at 10 minutes after injection, which slightly decreased but still accumulated at 2 hours later (Fig. 2)
Summary
Mixed tumors can occur in soft tissue as well as in the skin and soft palate [1,2], only 18 cases have been described to be primary in soft tissue [3,4]. Mixed tumors of soft tissue demonstrate similar histological features to pleomorphic adenomas of the salivary glands, having both benign and malignant forms in the same way. We present a case of benign mixed tumor arising in the subcutis, which demonstrated an early uptake of Tl-201 with slightly decreased accumulation in the delayed scan.
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