Dedifferentiated liposarcoma with peculiar meningothelial-like whorling and metaplastic bone formation.

Dedifferentiated liposarcoma with peculiar meningothelial-like whorling pattern and metaplastic bone formation (DDLMB) is an unusual morphologic entity that is characterized by an atypical lipomatous tumor/well-differentiated liposarcoma with epithelioid or spindle cells concentrically arranged into meningothelial-like "whorls," and mature bone trabeculae rimmed by reactive osteoblasts. We recently experienced 2 cases of DDLMB, one in a 64-year-old male patient with a painless right groin mass and another in a 42-year-old female patient with a painless right abdominal mass. The size of the tumors was 3.5 and 18 cm; and the tumors were located in the right scrotal sac and retroperitoneum in case 1 and case 2, respectively. Under the initial clinical diagnosis of cord lipoma in case 1 and high-grade sarcoma in case 2, the masses were removed. The cut surfaces of the masses were well circumscribed with encapsulation, red-tan, firm, and multinodular. Microscopically, the tumors consisted of atypical lipomatous tumor/well-differentiated liposarcoma with meningothelial-like whorls and metaplastic bone formation in both cases. In addition, the first case showed focal areas of paraganglioma-like pattern; and the second case showed pleomorphic high-grade sarcoma with low-grade myxofibrosarcoma-like areas. Immunohistochemically, the tumor components with meningothelial-like pattern and paraganglioma-like pattern in DDLMB were positive for vimentin and CD56 and negative for pancytokeratin, epithelial membrane antigen (EMA), desmin, and smooth muscle actin. Characteristically, the paraganglioma-like area was immunoreactive for S-100 protein, with a "dot-like" staining pattern. The patient additionally underwent radical orchiectomy in case 1. Review of the literature revealed that only 34 cases of DDLMB have been reported. One case of dedifferentiated liposarcoma with a predominant paraganglioma-like pattern has also been reported in the literature. To our knowledge, case 1 represents the first report of DDLMB with paraganglioma-like pattern. A brief literature review was made with focus on the morphologic variations of DDLMB.