Clinical History:
A 56 year old man was seen for a slow-growing, indolent subcutaneous mass on
his left back. The tumor measured 9 x 7 x 5 cm, was well-circumscribed but unencapsulated, and was
located above the fascia. The lesion was completely excised.
Case 6 - Figure 1 - Scanning magnification showing sparsely cellular lesion composed of areas showing dense collagen bundles admixed with mature fat, and areas composed of sparse collagen bundles against a prominentl myxoid background.
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Case 6 - Figure 2 - Predominantly myxoid area showing admixture of collagen bundles and mature fat surrounded by a proliferation of bland spindle and stellate cells.
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Case 6 - Figure 3 - Higher magnification showing small spindle cells with hyperchormatic nuclei and occasional elongated cytoplasmic prolongations (center).
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Pathologic findings:
At surgery, a 5.5 x 3.0 x 3.0 cm, ill-defined, unencapsulated soft tissue
mass was removed. The cut surface showed yellow-gray, glistening soft tissue with a mucoid consistency.
On histological examination, the lesion showed an admixture of three principal elements: mature adipose
and fibrous tissue embedded in abundant myxoid matrix, and a proliferation of small, stellate to spindle
cells with scant cytoplasm and hyperchromatic nuclei devoid of atypia or mitotic activity. No lipoblasts
or atypical adipocytes could be identified. Scattered small lymphocytes, plasma cells and mast cells
were also present. The lesion contained a well-developed vascular network composed of small to
medium-sized vessels, some of which adopted a curvilinear or plexiform configuration.
Immunohistochemical stains showed strong positivity of the spindle cells for CD34 and bcl-2, and negative
staining with actin, smooth muscle myosin, desmin, S-100 protein and cytokeratin. The myxoid stromal
component showed strong reaction with alcian blue stains at 2.5 pH; the reaction was abolished after
treatment with hyaluronidase.
Diagnosis - Dendritic Fibromyxolipoma
Comment:
Dendritic fibromyxolipoma (DFML) is a recently described entity that is characterized
by a combination of various elements that can resemble either a spindle cell lipoma or a solitary fibrous
tumor.1 In the cases reported in the literature, the tumors showed a predilection for adult men (mean
age: 64 years) and were located in the head and neck region, chest and back. The tumors are usually
well-circumscribed and unencapsulated, with a lobulated, yellow white and glistening cut surface
displaying a mucoid appearance. The size of the lesion may vary from 2 to 11 cm. (mean size: 6 cm).
Histological examination usually shows an admixture of several cellular elements in various proportions,
including mature fat, mature collagen, and a diffuse proliferation of spindle cells set against an
abundant myxoid stroma. Bland cytologic features characterize the spindle and stellate cells, with
hyperchromatic nuclei showing an evenly distributed dense chromatin pattern. The cells also contain
delicate, thin, elongated dendritic cytoplasmic prolongations that are more often best appreciated with
the use of special stains. The cells are remarkably uniform in appearance and usually do not display
cytologic features of malignancy or mitotic activity. Another important component of these lesions is
the presence of a prominent vascular network, which is composed of small to medium sized vessels that can
often adopt a "chicken-wire" appearance. When such vessels are present within heavily myxoid areas they
can closely mimic myxoid liposarcoma.
Immunohistochemical studies showed strong positivity of the spindle cells with antibodies against CD34
and bcl-2,1 and negative staining for muscle specific actin, desmin, S-100 protein, and cytokeratin.
The above features are similar to those encountered in other types of benign and malignant fibroblastic
proliferations of soft tissue such as solitary fibrous tumor, spindle cell lipoma, and other soft tissue
lesions of fibroblastic lineage.2-4 Ultrastructural studies have confirmed the dendritic nature of
the spindle cells, which show slender cytoplasmic processes lacking external lamina and foci of
pinocytotic activity.1
Differential diagnosis:
Due to the variegated composition of the lesions, the differential
diagnosis for these tumors can be quite broad, and includes benign and malignant soft tissue lesions. In
our study, because of their relatively large size and some of their particular histologic features, four
of the cases were initially misdiagnosed for a malignancy by the contributing pathologist.1 Three
cases were diagnosed as myxoid liposarcoma, and one case as a myxoid malignant fibrous histiocytoma.
Among the benign lesions, DFML is distinguished from a "true" myxolipoma because the latter generally
lacks prominent collagenization as well as a spindle cell component admixed with the myxoid stroma.
Another benign condition that shares many features with DFML is spindle cell lipoma.5,6 Spindle cell
lipoma (SCL) shares with DMFL its predilection for the head and neck, the bland-appearing proliferation
of spindle cells admixed with mature adipose and fibrous tissue, and an identical immunohistochemical
profile. In fact, a recent review article by Guillou and Coindre 7 on newly described adipocytic
lesions suggested that dendritic fibromyxolipoma may simply represent a myxoid variant of SCL. We
believe DFML is probably a very closely related lesion to SCL, but sufficiently distinctive that it
should merit separation from it.
A few subtle features help separate SCL from DFML. The spindle cell proliferation in SCL is usually
compact andtends to form fascicles, while the spindle cells in DFML do not grow forming bundles or
fascicles but are usually widely separated and scattered throughout the myxoid and fibrous areas.
Additionally, the spindle cells in SCL are usually elongated and fibroblast-like, unlike the short, oval
or stellate cells in DFML which display characteristic dendritic cytoplasmic prolongations. Although
there are a few isolated cases of SCL described in the literature that showed prominent myxoid changes,
the latter does not generally constitute a prominent feature in this condition. From the description of
the latter cases, we believe they probably represent examples of DFML, a condition not yet described at
the time of publication of those papers.6,8
Another benign, superficial soft tissue tumor that may also be characterized by a prominent myxoid
stromal component is solitary fibrous tumor of soft tissue.9,10 Such lesions also show a predilection
for the head and neck region in adult men, and present as well-circumscribed masses in subcutaneous or
fascial distribution. Histologically, they are characterized by a bland proliferation of spindle cells
that may adopt a variety of growth patterns. A characteristic feature is the deposition of rope-like
strands of thick keloidal collagen admixed with the spindle cells. The spindle cells also stain strongly
positive with CD34 and bcl-2.3,9 These lesions differ from our cases, however, by the absence of the
mature adipose tissue component.
Prognosis and behavior:
DFML is a benign condition. In all the cases in our series,1 none
recurred or metastasized despite the treatment being limited to local conservative excision. The main
importance of recognizing this condition lies in avoiding a misdiagnosis of a malignant neoplasm.
DFML shows some degree of overlap with both SCL and solitary fibrous tumor. Because of their distinctive
combination of morphologic features, we believe these lesions deserve separate recognition from both of
the above. It is likely that all three represent simply different manifestations or phases of the same
process. The possibility, for example, that spindle cell lipoma may represent a solitary fibrous tumor
that happens to be arising within fat rather than a neoplastic proliferation of "preadipocytes" as
originally proposed, has been previously postulated by some.2,11 Because of the potential for these
lesions to be confused for a malignancy, we believe that awareness of this entity is of importance to
avoid unnecessary aggressive treatment.
References
- Suster S, Fisher C, Moran CA. Dendritic fibromyxolipoma. Clinicopathologic study of a distinctive
benign soft tissue lesion that may be mistaken for a sarcoma. Ann Diagn Pathol 2:111-120, 1998.
- Suster S, Fisher C. Immunoreactivity of the human progenitor cell antigen (CD34) in lipomatous
tumors. Am J Surg Pathol 21:195-200, 1997.
- Suster S, Fisher C, Moran CA. Expression of bcl-2 oncoprotein in benign and malignant spindle cell
tumors of soft tissue, skin, serosal surfaces and gastrointestinal tract. Am J Surg Pathol 22: 863-872,
1998.
- Van de Rijn M, Lombard CM, Rouse RV. CD34. A review. Appl Immunohistochem 2:71-80, 1994.
- Enzinger FM, Harvey DA. Spindle cell lipoma. Cancer 36: 1852-1859, 1975.
- Angervall L, Dahl I, Kindblom LG et al. Spindle cell lipoma. Acta Pathol Microbiol Scand A84:
477-487, 1976.
- Guillou L, Coindre JM. Newly described adipocytic lesions. Semin Diagn Pathol 28: 238-249, 2001.
- Fletcher CDM, Martin-Bates E. Spindle cell lipoma: a clinicopathological study with some original
observations. Histopathology 11: 803-817, 1987.
- Suster S, Nascimento AG, Miettinen M et al. Solitary fibrous tumor of soft tissue. A
clinicopathologic and immunohistochemical study of 12 cases. Am J Surg Pathol 19: 1257-1266, 1995.
- De Saint Aubain Somerhausen N, Rubin BP, Fletcher CD. Myxoid solitary fibrous tumor: a study of
seven cases with emphasis on differential diagnosis. Mod Pathol 12: 463-471, 1999.
- Maggio P, Szumigala J, Brooks JJ. CD34 positive spindle cell lipoma. Are some cases incipient
solitary fibrous tumors? Mod Pathol 9: 10A, 1996.
