A Rare Case of Extradigital Glomus Tumour with Interesting Histopathological Findings

CASE DESCRIPTION

Glomus tumours are rare, hamartomatous proliferations of glomus cells, along with vasculature and smooth muscle. The classical clinical features include severe paroxysmal pain, localised tenderness and cold hypersensitivity. The most common location of glomus tumours is the subungual area of the hand fingers. Extradigital sites have been infrequently reported and the diagnosis is often difficult due to their rarity and lack of distinct clinical features in the physical examination, which can cause diagnostic delay. Herein, we report a rare case of extradigital glomus tumour with unusual histopathological features.

A 66-year-old male presented with a small painful lesion over his left calf for the past 3 years. There was no history of discharge or bleeding from the lesion. There was no prior history of local trauma.

On examination, it was a well-circumscribed, skin-coloured papule over the left calf [Figure 1]. On palpation, it was firm, mobile, non-compressible and tender. Dermoscopy was not done on the patient. An excision biopsy was done with a provisional diagnosis of leiomyoma, solitary neuroma, dermal melanocytic nevus, benign appendageal tumour and glomus tumour.

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Figure 1:

A well-circumscribed, skin-coloured papule over the left calf. Inset: closer view of the lesion.

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HISTOPATHOLOGICAL FINDINGS

Histopathological examination on routine haematoxylin and eosin stain showed multiple well-circumscribed, irregular nests of uniformly stained basophilic cells without any epidermal connection in one half of the section. The other half showed multiple dilated vascular channels with peri-vascular round cells with many of these cells showing a punched-out nucleus and pale eosinophilic cytoplasm. The intervening stroma was pale and homogeneous. The histopathology, therefore, showed two different histological types of glomus tumour in the same section, namely solid glomus tumour and glomangioma [Figure 2]. Smooth muscle actin (SMA) immunohistochemistry showed differential staining of cells; the solid nests of basaloid cells were positive and the cells in the perivascular location were negative or only weakly positive [Figure 3]. Similar findings were observed on periodic acid–Schiff (PAS) stain with the basaloid cells showing positivity, and the cells in the perivascular location were negative or only weakly positive [Figure 4].

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Figure 2:

(a) Photomicrograph showing mid-dermal irregular nests of uniformly stained basophilic cells on the left half of the section and dilated vascular channels with peri-vascular round monomorphic cells on the right half of the section (black arrows) (haematoxylin and eosin [H&E], ×100). (b) Multiple well-circumscribed, irregular nests of uniformly stained basophilic cells without any epidermal connection (black arrow) (H&E, ×400). (c) Multiple dilated vascular channels with peri-vascular round cells with punched-out nucleus and pale eosinophilic cytoplasm (black arrow). The intervening stroma is pale and homogenous (H&E, ×400). (d) Round cells with punched-out nucleus and pale eosinophilic cytoplasm in a pale and homogenous intervening stroma (black arrows) (H&E, ×400).

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Figure 3:

(a) Solid nests of basaloid cells showing smooth muscle actin (SMA) positivity (SMA, scanner view). (b) Cells in the perivascular location were SMA negative or only weakly positive (SMA, ×100). (c) Glomus cells in the nests showing SMA positivity (SMA, ×400). (d) Cells with staining negative or only weakly positive (SMA ×400).

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Figure 4:

Tumour cells showing focal positivity with PAS stain in solid nests and in perivascular area (black arrows) (PAS, 100X).

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DIAGNOSIS

Based on clinical features and histopathological findings, diagnosis of glomus tumour was made.

DISCUSSION

The glomus body is composed of an afferent arteriole and an efferent venule, with glomus cells that contract on cold stimuli and are involved in thermoregulation. Glomus tumours are rare, hamartomatous proliferations of these glomus cells, along with vasculature and smooth muscle. They account for 1–2% of all soft tissue tumours. The most common affected age group is the third to fourth decade and they are usually solitary.^[1] The most common site of involvement is the subungual area of the fingers, where the classical presentation includes severe paroxysmal pain, localised tenderness and cold hypersensitivity.

Lee et al. demonstrated that extradigital glomus tumours are more common in males, whereas digital tumours are more frequent in females.^[1] In a study of 52 cases of glomus tumours at extradigital sites, thighs, calf and ankle, foot, buttocks, trunk/abdomen, arm and wrist/hand were the atypical sites seen in decreasing order of frequency.^[1] Rarely, internal organs may also be involved.

The location on the calf is an extremely unusual site. Only a few cases of glomus tumour on the lower extremity have been reported so far, out of which, to the best of our knowledge, only 5 cases have presented with lesions on the calves.^[1-5] In a series of 56 patients with extradigital glomus tumours, only three cases had leg as the tumour site. In glomus tumours of the lower extremities, musculoskeletal involvement can present as chronic paroxysmal pain in the affected extremity associated with limb atrophy.

On histopathology, the tumour is lobulated, well circumscribed and situated in the dermis, composed of vascular channels and glomus cells. Typically, the glomus cell is cuboidal to round, with a well-marked cell membrane, eosinophilic cytoplasm and a round central basophilic punched-out nucleus. The cells align themselves in rows around the single layer of endothelial cells of the vascular spaces. Three histological types of glomus tumours have been described: Solid glomus tumour, glomangioma (also known as glomuvenous malformation) and glomangiomyoma. Solid type shows sheets of glomus cells in the dermis. Glomangiomas have a prominent vascular component with dilated vascular channels surrounded by glomus tumour cells. Smaller painful lesions are predominantly cellular while larger painless ones are mainly angiomatous, with only a band of glomus cells around the dilated vascular channels. Glomangiomyomas contain both vascular and smooth muscle tissue. In a retrospective study on 137 cases of glomus tumours, 84 (61%) were extradigital, out of which 56 patients were biopsied out of which majority (n = 42, 75%) were solid glomus tumours, 12 (21%) were glomuvenous malformations and 2 (4%) were glomangiomyoma.

Immunohistochemistry is positive for SMA and vimentin and usually negative for desmin. Positivity for CD34 may be seen in 25% of cases.

The histopathology in our case showed differential staining on SMA and PAS stain with strongly positive basaloid cells and negative/weakly positive perivascular glomus cells. Considering the above, the lightly staining cells could possibly represent a more mature part of the tumour with the staining becoming lighter as the tumour cells evolve and mature.

Glomus tumours rarely metastasise but have a potential for local recurrence. The diagnostic aids for evaluating glomus tumours include ultrasonography, magnetic resonance imaging and histopathology. Differential diagnosis includes leiomyoma, angiolipoma, neuroma, eccrine spiradenoma, cavernous haemangioma and blue rubber bleb nevus. Treatment of choice is surgical excision. Less commonly, laser ablation (argon or carbon dioxide) and sclerotherapy have been tried.

Our case is unique in certain aspects, first, the unusual site of the lesion and lack of typical pink-to-purple hue. Second, the presence of two described histological types of glomus tumour in the same lesion with differential staining patterns on SMA and PAS stain is an interesting histopathological finding. Extradigital glomus tumours are rare and often lack the distinct clinical features as described for classical subungual cases, and therefore, it is important for the clinician to be aware of this entity and include in the list of differentials.