Liposarcoma with meningothelial-like whorls: a study of 17 cases of a distinctive histological pattern associated with dedifferentiated liposarcoma.

AIMS: We reviewed 17 cases of liposarcoma with peculiar meningothelial-like whorls to determine the pathological and clinical significance of this distinctive morphological finding. METHODS AND
RESULTS: Seventeen liposarcomas with concentric whorls simulating the whorls seen in meningioma, were retrieved from the soft tissue registry of the Armed Forces Institute of Pathology. There were 10 males and seven females with a mean age of 53 years (range 24-76 years). Twelve of the 17 cases were large retroperitoneal tumours (mean 170 mm in greatest dimensions). All 17 cases had whorls. Three cases were classified as well-differentiated liposarcoma with whorls and bone formation. Five cases showed coalescing of whorls into areas which may be interpreted as low to intermediate grade dedifferentiation. Five cases had spindled areas associated with the whorls which correlate with classical intermediate to high-grade dedifferentiation. Finally, four cases had a predominant spindle cell component resembling malignant fibrous histiocytoma with focal residual possible sclerosing well-differentiated liposarcoma (scattered adipocytes, adipocytic atypia and/or floret-type giant cells). The meningothelial-like whorls were clustered or scattered throughout the tumours and ranged from 0.09 mm to over 10 mm in diameter in cases with coalescent whorls. Metaplastic bone was present within the whorls or in their immediate vicinity in 10 of 17 cases. Immunohistochemically, the whorl-forming spindle cells showed alpha-smooth muscle actin reactivity in three of seven cases but were negative for epithelial membrane antigen, CD21, and CD35 indicating lack of relationship with meningioma and dendritic reticulum cell sarcoma, other tumours that may contain whorls. Whorls with bone formation revealed cells adjacent to the bone to be positive for osteocalcin, a marker of osteoblastic phenotype. The spindle cells of the whorls were negative for CD34 and CD31, yet these highlighted numerous capillaries inside the whorls in a concentric manner. The whorl-forming cells showed moderate to high MIB-1-index and showed p53 immunoreactivity similar to the dedifferentiated areas but differed from the areas of well-differentiated liposarcoma, which were p53-negative and showed a low MIB-1-index. Follow-up (available in 65% cases) revealed seven patients with metastases or dead of the disease and five patients with one or more recurrences.
CONCLUSIONS: The meningothelial-like whorls represent a mesenchymal proliferation which may undergo pericytic or myofibroblastic, or occasionally osteoblastic, differentiation in liposarcoma. These whorls do not represent dendritic or perineurial/meningothelial differentiation. The significant proliferative activity, p53 reactivity and tendency to coalesce and associate with dedifferentiated liposarcoma suggest that the meningothelial whorls may represent an early sign of dedifferentiation of liposarcoma.