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 dis tinctive morphological finding. Methods and results: Seventeen liposarcomas with concentric whorls simulati ng the whorls seen in meningioma, were retrieved from the soft tissue regis try of the Armed Forces Institute of Pathology, There were 10 males and sev en females with a mean age of 53 years (range 24-76 years), Twelve of the 1 7 cases were large retroperitoneal tumours (mean 170 mm in greatest dimensi ons). All 17 cases had whorls. Three cases were classified as well-differen tiated liposarcoma with whorls and bone formation. Five cases showed coales cing of whorls into areas which may be interpreted as low to intermediate g rade dedifferentiation. Five cases had spindled areas associated with the w horls which correlate with classical intermediate to high-grade dedifferent iation, Finally, four cases had a predominant spindle cell component resemb ling malignant fibrous histiocytoma with focal residual possible sclerosing well-differentiated liposarcoma (scattered adipocytes, adipocytic atypia a nd/or floret-type giant cells), The meningothelial-like whorls were cluster ed or scattered throughout the tumours and ranged from 0.09 mm to over 10 m m in diameter in cases with coalescent whorls. Metaplastic bone was present within the whorls or in their immediate vicinity in 10 of 17 cases. Immuno histochemically, 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 menin gioma and dendritic reticulum cell sarcoma, other tumours that may contain whorls. Whorls with bone formation revealed cells adjacent to the bone to b e 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-f orming cells showed moderate to high MIB-1-index and showed p53 immunoreact ivity similar to the dedifferentiated areas but differed from the areas of well-differentiated liposarcoma, which were p53-negative and showed a low M IB-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 recur rences. Conclusions: The meningothelial-like whorls represent a mesenchymal prolife ration which may undergo pericytic or myofibroblastic, or occasionally oste oblastic, differentiation in liposarcoma, These whorls do not represent den dritic or perineurial/meningothelial differentiation. The significant proli ferative activity, p53 reactivity and tendency to coalesce and associate wi th dedifferentiated liposarcoma suggest that the meningothelial whorls may represent an early sign of dedifferentiation of liposarcoma.