Dendritic fibromyxolipoma is a rare benign soft tissue tumour that was
first reported by Suster et al. in 1998 in twelve patients.
(2) Since then, only 24 cases have been reported in the English literature and cited in Pub Med.
(3) The tumour most commonly arises in the subcutaneous tissue of subcutis or muscular fascia of the head, neck, back, chest wall and shoulder, other rare sites including muscle, lip, median nerve and nasal tip.
(4) Dendritic fibromyxolipoma often occurs in older males, presenting as a slowly growing mass, which is described as a well-demarcated, encapsulated soft-tissue mass, with a gray-yellow, mucoid or gelatinous cut surface.
(5) The most striking histologic feature of Dendritic fibromyxolipoma is an admixture of mature adipose tissue, spindle and stellate cells, abundant myxoid stroma with prominent collagenization and a prominent delicate plexiform capillary vascular network which is present throughout the tumour.
(6) Immunohistochemically, the CD34, Bcl-2 and vimentin immunohistochemical stains accentuate the cell's dendritic nature by revealing slender, complex cytoplasmic prolongations.
(7) The adipocytes, but not the spindle or stellate cells, show positive staining for S-100 protein and staining for cytokeratin, epithelial membrane antigen, smooth muscle actin and desmin is also negative.
(8) Dendritic fibromyxolipoma should be differentiated from some benign lesions: spindle cell lipoma, solitary fibrous tumour, lipoblastoma, lipoblastomatosis, and nodular fascitis.
(9) Due to the presence of abundant myxoid matrix and proliferation of capillaries, dendritic fibromyxolipoma can be misdiagnosed as myxoid liposarcoma, myxofibrosarcoma and low-grade fibromyxoid sarcoma. Careful microscopic examination and a panel of immunohistichemistry can lead to a correct diagnosis.
(10) Of the other tumour-like lesions, spindle cell lipoma is most likely to be confused with dendritic fibromyxolipoma.
Spindle cell lipoma is composed of a mixture of mature adipocytes and uniform spindle cells within a matrix of mucinous material traversed by a varying number of birefringent collagen fibers and shares many features with dendritic fibromyxolipoma including age, male predilection, location, gross features. Suster et al. emphasized the dendritic nature of the spindle cells, the plexiform vascular pattern, and the abundance of keloidal collagen as the three essential features in dendritic fibromyxolipoma, which are not commonly present in spindle cell lipoma.
(11) Other benign spindle cell tumour that should be distinguished from dendritic fibromyxolipoma is solitary fibrous tumour.
Solitary fibrous tumours which have a predilection for the thoracic cavity are rare fibrous neoplasms. Histologically, the tumour is characterized by a "patternless pattern" of short spindle cells with scant cytoplasm and bland cytologic appearance separated by strands of rope-like collagen, and a "hemangiopericytoma-like" pattern where the lesional cells are densest around small and medium ectatic and branching vessels.
(12) Lipoblastoma and lipoblastomatosis are another two rare benign soft tissue mesenchymal tumours that may be confused with dendritic fibromyxolipoma.
The tumours mainly occur almost exclusively in infants and children under the age of 3 years. The common microscopic features of lipoblastoma and lipoblastomatosis have been described as a mixture composed of immature lipoblasts,mature lipocytes, embedded in an abundant myxoid stroma. Dendritic fibromyxolipoma can be easily distinguished from lipoblastoma and lipoblastomatosis by the patients age and the absence of lipoblasts.
(13) Nodular fascitis is another lesion that should be differentiated from dendritic fibromyxolipoma.
Nodular fascitis shows proliferating spindle cells embedded in a loosely textured myxoid and inflammatory stroma. Unlike dendritic fibromyxolipoma, the lesion is relatively well circumscribed but poor encapsulated. Immunohistochemically, the spindle cells are positive for muscle markers except desmin and are S-100 protein and CD-34 negative.
(14) Dendritic fibromyxolipoma has abundant myxoid stroma and a prominent plexiform vascular pattern reminiscent of that observed in myxoid liposarcoma, therefore, the tumor may be mistaken for a myxoid liposarcoma,
Myxoid liposarcoma often occurs in the deep soft tissue, especially in lower extremities and retroperitoneum. The tumor is characterized by the presence of lipoblasts and invasive growth. Immunohistochemically, most of the tumour cells are positive for S-100 protein, while negative for CD34 protein. Moreover, almost all (>95%) myxoid liposarcomas involve chromosomal translocations of t(12;16)(q13;p11) and t(12;22)(q13;q12).
(15) Myxofibrosarcoma and low-grade fibromyxoid sarcoma should be distinguished from dendritic fibromyxolipoma.
Myxofibrosarcoma is generally characterized by a significant degree of nuclear pleomorphism and occasional mitotic figures. The important features are vacuoles of thepseudolipoblasts and a vascular pattern characterized by large curvilinear vessels. Low-grade fibromyxoid sarcoma exhibits myxoid areas and cytologically bland spindle cells. The spindle cells are characterized by whorled or swirling growth patterns.
(16) When a myxoid spindle cell tumour is diagnosed, dendritic fibromyxolipoma should be considered. It is important to avoid misdiagnosis of more aggressive neoplasms.
Liu S, Wang X, Lei B, et al. Dendritic fibromyxolipoma in the latissimus dorsi: a case report and review of the literature. International Journal of Clinical and Experimental Pathology. 2015;8(7):8650-8654.
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