Aneurysmal dermatofibroma: An uncommon variant of a common disease

Dear Sir,

Aneurysmal dermatofibroma is an uncommon variant of dermatofibroma that closely mimics tumors such as Kaposi sarcoma, angiosarcoma, and malignant melanoma. As compared to classic dermatofibroma, this variant is larger in size, soft in consistency, has accelerated growth, and is often painful. We hereby present a case of aneurysmal dermatofibroma in a middle-aged female.

A 37-year-old female presented with an asymptomatic nodular swelling over the left periumbilical area for the past four years. She noticed an increase in size and intermittent pain for the last three months. There was no history of prior trauma, bleeding, or ulceration from the lesion. Clinical examination revealed a solitary bluish-brown nodular swelling of size measuring approximately 2 x 2 cm on the left side of the abdomen [Figure 1a]. It was soft, tender, non-blanchable, and had no local rise in temperature, thrill, or bruit. Dermoscopy showed a bluish-purplish, prominent, homogeneous area, shiny white structures, and fine white scaling [Figure 1b].

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Figure 1: (a) A well-circumscribed bluish-brown nodular swelling seen on the left side of the abdomen; (b) Dermoscopy showed a bluish-purplish prominent homogeneous area in the background (black star), shiny white structures arranged in linear streaks (black triangle) and fine white scaling (black arrow) (Dermlite 4 in non-polarised mode at 20x magnification).

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Differential diagnosis of dermatofibroma (DF), Kaposi sarcoma (KS), and spindle cell angiosarcoma was considered, and a skin biopsy was sent for histopathological examination. Biopsy revealed a well-circumscribed dermal tumor composed of thin, elongated, spindle-shaped cells arranged in a focal storiform pattern with irregular borders, peripheral collagen trapping, and pseudo-vascular space in the center, which was not lined by endothelial cells. There were admixed hemosiderin-laden histiocytes. The Grenz zone was noted between the tumor and the overlying epidermis. The tumor cells showed moderate nuclear atypia with coarse chromatin and a mitotic rate of 7-8 per 10 high-power fields. However, no atypical mitoses, necrosis, or infiltration were noted [Figures 2a and b]. To further characterize the tumor cells, immunohistochemistry was done, which showed diffuse positivity for cluster of differentiation (CD)10 and focal positivity for CD68 [Figures 2c and d]. There was no positivity found for CD34, smooth muscle antigen (SMA), human melanoma black (HMB)45, desmin, melan A, SOX10, estrogen receptor (ER), CD31, PAX8, CK7, CD45, epithelial membrane antigen (EMA) and anaplastic 28 lymphoma kinase (ALK). Based on both histopathology and immunohistochemistry (IHC) findings, a final diagnosis of aneurysmal dermatofibroma was made, and the patient underwent surgical excision with no local recurrence after six months of follow-up.

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Figure 2: (a) Histopathology revealed a circumscribed dermal tumour with an irregular border, peripheral collagen trapping and pseudovascular space in the central region (black star). The Grenz zone is seen (bracket). Hypocellular and hypercellular areas seen (hematoxylin and eosin, 20x); (b) thin elongated spindle cells with admixed histiocytes with pale eosinophilic cytoplasm (black arrow) and hemosiderin within them (black star) (hematoxylin and eosin, 200x); (c) tumour cells with diffuse CD10 positivity (CD 10 IHC, 200X); (d) histiocytes with CD68 positivity (CD68 IHC, 200x). IHC: Immunohistochemistry

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DF or benign fibrous histiocytoma is a commonly occurring dermal tumor. Multiple variants of dermatofibroma have been identified in the literature, which include cellular DF, aneurysmal DF, hemosiderosis DF, epithelioid DF, atrophic DF, ulcerated DF, erosive DF, and lichenoid DF.^[1,2] Clinically, aneurysmal DFs are characterized by benign, slow-growing nodular lesions that are soft in consistency and can have associated pain. It occurs due to intra-tumoral bleeding, which can explain the soft consistency, larger size, and more painful nature of this variant as compared to the typical dermatofibroma.^[3] Histopathologically, it shows multiple spindle-shaped cells in a storiform pattern with hemosiderin-laden giant cells and macrophages, which are interspersed with small capillaries without endothelial atypia. It classically shows large blood-filled spaces not bound by the typical endothelial lining of vascular structures.^[2] It is crucial to distinguish the benign aneurysmal DF from its worrisome clinical mimics, including KS and angiosarcomas. KS was ruled out in our case, as it classically lacks the presence of fibrohistiocytic cells and has slit-like spaces containing red blood cells, and shows CD34 positivity. Also, KS is associated with human herpesvirus (HHV) - 8 and human immunodeficiency virus(HIV) infection and shows positivity for c-kit (ki-67). Cutaneous angiosarcoma usually occurs on the scalp in the elderly population. It shows irregular anastomosing vessels with atypical endothelial cells and mitotic figures that dissect through the underlying dermis, forming the network. Angiosarcoma shows positivity to CD31 and CD34 on IHC.^[4,5] As both CD 31 and CD 34 were negative in our case, and histopathology also did not favor the features of angiosarcoma. Aneurysmal DF generally has a favorable prognosis, and surgical excision is considered the first-line treatment option. But this variant has a higher recurrence rate, reaching up to 20%, which is significantly higher than the classic DF, which shows less than 2% recurrence rates.^[3] Surgical excision was done for our case, and there were no recurrences at six months of follow-up. However, she was advised to do regular follow-up visits as there is a high chance of recurrence.

It is crucial to differentiate aneurysmal DF from its close mimics, like vascular and malignant tumors, as the prognosis and management of these entities differ. Although they can be differentiated on the basis of histopathological examination, sometimes it might be difficult. Additional investigations that help in differentiation include special stains like Prussian blue and IHC. Siderophiles in aneurysmal DF are Prussian blue positive, and IHC is positive for vimentin and negative for factors CD31, CD34, desmin, and CD8.^[3] Subtle histopathological changes and additional specific investigations, as mentioned, can help reach an accurate diagnosis.