Dermoscopy of Solitary Epithelioid Histiocytoma of the Scalp: A Novel Feature.

A 31-year-old male presented with complaint of a sudden onset and rapidly growing painless lesion on the scalp of 15 days duration with no preceding history of trauma or insect bite. Examination showed a solitary, firm, well-defined erythematous nodule measuring 1 × 1 cm with smooth non-exudative surface [Figure 1]. There were no palpable lymph nodes and no other systemic abnormalities.

Figure 1

Nodule with a smooth non exudative surface

Dermoscopy of the lesion showed a central yellow orange area [Figure 2a] with superficial white scales overlying structureless areas [Figure 2b] in the periphery. Linear curved vessels of different lengths arranged in a parallel array were seen around the central yellow area [Figure 2b].

Figure 2

Dermoscopic image (Dermlite, DL1, USA, 10X, polarised) (a) Red arrow -setting sun sign; (b) Blue arrow - superficially attached white scales overlying structureless areas, Green arrow – ‘appearance

Excision biopsy of the lesion showed infiltrate composed of large cells with vesicular nuclei and small prominent nucleoli and few cells showing folded crumpled membrane along with diffuse infiltrate of lymphocytes and eosinophils along with occasional giant cells [Figure 3 and 4]. Immunohistochemistry showed that cells were positive for CD68 and stained weakly for S100 and CD1a. CD34 was restricted to endothelial lining.

Figure 3

(a). Photomicrograph showing normal epidermis with papillary dermis, reticular dermis and subcutaneous tissue showing infiltrate composed of large cells with vesicular nuclei and a diffuse infiltrate of lymphocytes and eosinophils. The pilosebaceous units appear normal. (H and E, 100×). (b). Photomicrograph showing large cells with vesicular nuclei and small prominent nucleoli with few cells showing folded crumpled membrane with a diffuse infiltrate of numerous lymphocytes and eosinophils in the background (H and E, 1000×)

Figure 4

Photomicrograph collage showing showing large cells with vesicular nuclei and small prominent nucleoli with few cells showing folded crumpled membrane. Numerous lymphocytes and eosinophils filled up the background (a) 10X; (b) 100X; (c) 400X; (d)1000X

Dermoscopy of solitary epithelioid histiocytoma, has an auxiliary role in its diagnosis.[1] There are only few reports of solitary epithelioid histiocytoma in which dermoscopy findings have been described earlier.

Few dermoscopic patterns previously reported are

Dotted vessel and light-brown globules on a yellow background[2]

Uniformly yellow central area and a pink-orange colour in the periphery—”Setting sun sign”[3]

Crown vessels and white dots were demonstrated along with the presence of light-yellow background in a recent study[4] as a result of congestion of capillaries and veins. Crown vessels consists of homogenously curved, slightly arborizing vessels which meet at the centre of the lesion.

Arborizing vessels have also been described in solitary histiocytomas which sometimes can mimic BCCs.[5]

In our case, an additional dermoscopy finding mimicking “raindrops falling on a windowpane” was observed. Unlike crown vessels, the vascular architecture in this case showed vessels arranged in a parallel configuration, with no arborisation and no convergence at any point. Hence the description of “raindrops on a window pane”.

This finding might be due to pooling of blood resulting from congestion of the venules, manifesting as “raindrops” on dermoscopy.

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The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.