| Abstract|| |
Pseudoangiomatous spindle cell lipoma is a rare variant of spindle cell lipoma. It exhibits irregular and branching spaces with villiform connective tissue projections, leading to formation of a characteristic angiomatoid pattern in addition to benign spindle cells and mature adipocytes. Recent studies have shown that these branching spaces are lined by endothelial cells and express markers. Therefore, the term “angiomatous variant” instead of “pseudoangiomatous” has been proposed for these lesions. We describe one of such lesions in the thumb of a young female. To the best of our knowledge, this is the first reported case of pseudoangiomatous variant of spindle cell lipoma from India.
Keywords: Angiomatous, lipoma, pseudoangiomatous, spindle cell, variant
|How to cite this article:|
Bhat A, Vijaya C, Rao SB. Pseudoangiomatous variant of spindle cell lipoma: Report of a rare case. Indian J Pathol Microbiol 2016;59:376-8
| Introduction|| |
Pseudoangiomatous spindle cell lipoma is a rare variant of spindle cell lipoma. The pathogenesis is uncertain. Very few cases have been reported in the past. The median age of presentation is 52 years and median size is 3 cm.
These lesions develop predominantly in the shoulder and cervical regions of adult males. The lesions exhibit features of typical spindle cell lipoma along with irregular and branching spaces with villiform connective tissue projections, which impart a striking angiomatoid appearance. Positivity of CD34 is strongly suggestive of diagnosis. To the best of our knowledge, this is the first case of pseudoangiomatous variant of spindle cell lipoma reported from India.
| Case Report|| |
A 30-year-old female presented with a slowly growing swelling in the left thumb since 1 year. On examination, the swelling measured about 1 cm × 1 cm and was located in the subcutaneous tissue plane. It was mobile and nontender. The overlying skin was unremarkable. There were no functional abnormalities of the thumb. The other fingers were unremarkable. There were no other swellings in the body. Fine-needle aspiration cytology was attempted, but it yielded only hemorrhage. Thus, an excision biopsy was performed. The gross specimen consisted of a gray-brown round to oval nodular structure with tiny yellow nodularities [Figure 1]a. The cut section showed brownish linear areas separated by gray-white areas and small yellowish areas [Figure 1]b. Histopathological examination showed a partially encapsulated lesion [Figure 1]c with nests and clusters of mature adipocytes separated by dense fibrocollagenous stroma containing occasional bland spindle cells and congested vascular channels [Figure 1]d. The collagenous stroma showed irregular branching cleft like vascular spaces lined by flattened cells filled with red blood cells [Figure 2]a. Villiform projections of connective tissue stroma into these cleft-like spaces covered by flattened cells were characteristically seen [Figure 2]b. A histopathological diagnosis of pseudoangiomatous variant of spindle cell lipoma was made. Immunohistochemical (IHC) marker CD34 was positive in the cytoplasm of the endothelial cells lining the characteristic “pseudoangiomatous” spaces and was diagnostic of the lesion [Figure 2]c and [Figure 2]d.
|Figure 1: Gross picture showing (a) occasional pale yellow nodule on the external surface, (b) brownish linear branching channels on cut section. Photomicrograph showing (c) the delicate fibrous capsule (H and E, ×100). (d) The sinusoidal branching channels and lobules of mature adipocytes (H and E, ×100)|
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|Figure 2: Photomicrographs showing (a) villiform connective tissue projections protruding into the lumen of irregular branching vascular channels (H and E, ×100), (b) surface of villiform projections lined by benign endothelial cells(H and E, ×400). (c and d) CD34 cytoplasmic positivity in the lining epithelial cells of sinusoidal vascular spaces (IHC-CD34, ×400)|
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| Discussion|| |
Spindle cell lipoma was first described in 1975. It is a unique variant of lipomas affecting chiefly the subcutaneous tissue of the neck, shoulder, and back and accounts for up to 1.5% of all adipocytic neoplasms. Chin, elbow, finger, and jaw are the unusual locations. It is characterized by the replacement of mature fat from spindle cells and eosinophilic collagen bundles, and has a benign clinical course. Several histological subtypes of spindle cell lipoma have been documented. Cutaneous spindle cell/pleomorphic lipoma presents as poorly circumscribed dermal nodule mainly affecting females. Histopathologically it shows floret giant cells in addition to benign spindle cells and adipocytes in a myxoid stroma. Dendritic fibromyxolipoma shows predominant myxoid stroma and the spindle cells display dendritic processes. In the fibrous variant, the major component of the lesion is the presence of dense fibrous stroma., The “pseudoangiomatous variant” which is now labeled by some authors as “angiomatous variant” displays endothelial lined spaces within the lesion.
Histologically, the pseudoangiomatous variant of spindle cell lipoma shows mixture of mature fat cells, short spindled stromal cells with bland regular nuclei, and blood vessels ranging in size from small capillaries to thick walled vessels containing smooth muscle bundles. The most characteristic feature is numerous irregularly branching sinusoidal channels that divide the tumor into lobules. They lack mitosis and atypia. Branching cleft-like spaces lined by flattened endothelial cells and villiform myxoid connective tissue projections into these spaces are characteristic., In our case, the connective tissue projections showed extensive sclerotic change.
Immunohistochemically, CD34 positivity is noted in spindled stromal cells, vascular endothelial cells, the flattened cells lining the surface of villiform projections, and cleft-like spaces. CD31 and factor VIII are positive in vascular endothelial cells, cells lining the cleft-like spaces, and villiform projections. Alpha smooth muscle actin shows focal positivity. Calponin shows positivity only in smooth muscle cells of the large vessels. Estrogen receptor, progesterone receptor, and androgen receptor show positivity in 50%, 70% and 40% of the tumor cells, respectively. S100 stains the adipocytes. CD10, cytokeratins AE1-AE3, and epithelial membrane antigen are negative in these tumors. In our case, IHC marker CD34 was used and it was positive in the cells lining the sinusoidal spaces and villiform projections.
The differential diagnosis of pseudoangiomatous variant of spindle cell lipoma includes spindle cell lipoma, fibrolipoma or sclerotic lipoma, angiolipoma, and angiomyolipoma. Vascular tumors such as retiform hemangioendothelioma may also resemble it at some foci.
Histopathologically, spindle cell lipomas show bundles of ropy eosinophilic collagen and benign spindle cells that function like fibroblasts arranged in fascicles. Numerous mast cells may be seen. These spindle cells are CD34 positive, S100, and desmin negative.
Fibrolipomas exhibit considerable amounts of fibroconnective tissue. Sclerotic lipomas show occasional bland spindle cells within dense fibrotic stroma. They lack irregular branching vascular channels and villiform projections of stroma into these channels.
Angiomyolipomas are composed of admixture of thick-walled medium-sized blood vessels from which sheets of plump smooth muscle cells appear to be derived and mature adipocytes. Cutaneous angiomyolipomas may not show HMB positivity. They may be CD34 positive. However, they lack the classical “pseudoangiomatous pattern.”,
Angiolipomas exhibit delicate small-sized vessels containing microthrombi intricately admixed with mature adipose tissue. These vessels do not display sinusoidal branching patterns.,
Although retiform hemangioendotheliomas show elongated, delicate branching vascular channels embedded in a sclerotic stroma, these channels are lined by hobnail endothelial cells. Furthermore, they lack mature adipocytes and exhibit stromal lymphocytic infiltrates. CD31 and 34 may be positive in the endothelial cells of these tumors.,
Aberrations of the 16q chromosome, unbalanced aberrations of the 13q chromosome, and simultaneous 13q abnormality and a ring chromosome have been associated with spindle cell lipomas.
| Conclusions|| |
Pseudoangiomatous variant of spindle cell lipoma is a rare variant of spindle cell lipoma. Very few cases have been reported in the past. The term “pseudoangiomatous variant” is a misnomer as the irregular branching spaces in this tumor are actually lined by CD34 positive endothelial cells and contain blood. Hence, we believe that the term “angiomatous” variant is more descriptive of this lesion.
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Conflicts of interest
There are no conflicts of interest.
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Dr. Amoolya Bhat
Department of Pathology, Sapthagiri Institute of Medical Sciences and Research Centre, #15Chikkasandra, Hesarghatta Main Road, Bengaluru - 560 090, Karnataka
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]