Angiomyoma vs solitary fibrous tumour – A histopathological dilemma

Introduction

Angiomyoma also known as vascular leiomyoma or Angioleiomyoma is one of the rare types of leiomyomas among its three histological groups- (i) vascular (angioleiomyoma), (ii) solid and (iii) epithelioid (leiomyoblastomas).^[1] It was first described in 1854 by Rudolf Virchow.^[2] Angioleiomyomas (AL) are the most common variants affecting the oral cavity, representing 64.0%–92.3% of all variants of oral leiomyoma.^[3] This may be due to the rich blood supply of the oral cavity. Clinically they are small, painless, slowly growing tumours located subcutaneously without superficial changes.^[4] Lips, palate, buccal mucosa and tongue are the commonly involved sites in the oral cavity.^[5] Commonly seen in the age group of 40 to 50 years with a slight male predominance and characterized histologically, as a well circumscribed lesion composed of a tortuous mass of thick walled blood vessels among mesenchymal spindle cells with eosinophilic cytoplasm and elongated basophilic cigar shaped nuclei.^[6] Due to the pain producing nature of cutaneous and vascular leiomyomas they were collectively termed ‘tubercular dolorosum’.^[7]

The clinical features of AL overlap with many other lesions of the oral cavity like mucocele, pleomorphic adenoma, mesenchymal tumors, lymphangioma, pyogenic granuloma, and schwannoma, solitary fibrous tumor etc. These lesions need to be ruled out before giving the diagnosis of AL. It requires a histopathological confirmation not only using regular H&E but special stains and IHC markers such as α-SMA, desmin, CD34 and HHF-35 are also required.^[8] Here we present a case of a long-standing swelling involving the upper lip of an adult male.

Case Presentation

A 65-year-old male presented to our department, with a chief complaint of swelling in his upper lip for 4 years. His medical history was unremarkable, and had no history of tobacco smoking or alcohol consumption. The patient was apprehensive about the labial growth. Upon eliciting the history, an oval-shaped peanut-sized swelling initially appeared along the midline of the upper lip, following blunt trauma to upper front teeth and lip which grew gradually over 4 years to reach the present size measuring approximately 1.5x2cms in size. The swelling was not associated with pain or any discomfort. On extraoral examination ([Figure 1] a) a solitary dome shaped swelling was seen extending superior-inferiorly from the vermillion border of the upper lip to 2cms downwards. The colour of the overlying mucosa was normal. Intraoral examination was unremarkable with generalised attrition, abrasion, gingival recession and root stumps. On palpation, the inspe ctory findings were confirmed. The mass was superficial, non-tender, smooth, sessile, movable, and firm. No fluctuation or bruit was present. The patient was afebrile, and there was no cervical lymph nodes enlargement. Based on the clinical findings a provisional diagnosis of traumatic fibroma and a differential diagnosis of minor salivary gland tumour was given.

The patient was advised oral prophylaxis after which he underwent an excisional biopsy under local anaesthesia under antibiotic prophylaxis ([Figure 1] b,c). The specimen was sent in formalin for histopathological analysis ([Figure 1] d). Whole of the tissue bit was taken for processing.

Microscopic examination of the H&E- stained section revealed a well-encapsulated lesion with hyper cellular and hypo cellular areas in connective tissue ([Figure 2] a). The hyper cellular areas show round to ovoid cells with vesicular nuclei and prominent nucleoli surrounding the blood vessels. Congested blood vessels are exhibiting slit like and stag horn pattern ([Figure 2] b). The hypo cellular areas show a dense hyalinised stroma interspersed with a few spindle-shaped cells. Histological differential diagnoses of Solitary fibrous tumour (SFT), Heamangipericytoma (HPC) and Angiomyoma were considered. However, numerous thick-walled, congested blood vessels were seen within these bundles of smooth muscle ([Figure 2] c). Individual smooth muscle cells possess abundant eosinophilic cytoplasm and elongated cigar-shaped nuclei ([Figure 2] d). These cells lack both nuclear hyperchromasia and significant numbers of mitosis. Mild inflammatory infiltrate composed of lymphocytes and few plasma cells are also seen. These features pointed towards Angiomyoma. To rule out confusion between SFT and Angiomyoma, Masson Trichrome staining was done which distinguishes smooth muscle and collagen by staining smooth muscle cells as red and collagen fibers as blue. As our case stained with this pattern, we could recognize the smooth muscle as the main part of the lesion. To further confirm our diagnosis, immunohistochemical staining was performed using SMA and H-caldesmon that showed a diffuse positivity which is characteristic of Angimyoma ([Figure 4] a, b). S100 was negative ([Figure 5] a) ruling out any neural tumours. On the other hand, CD34, CD99 were negative which are distinct markers in diagnosing SFT ([Figure 5] b, c).

A diagnosis of Angiomyoma was given based on the clinical features, histologic appearance under routine H&E stain, Masson Trichrome stain and IHC markers. The postoperative period was uneventful. For the year-long follow-up period after the surgical removal, no recurrence was noted.

Discussion

Angioleiomyoma (AML) are benign tumors of the vascular smooth muscle origin. They are rarely encountered in the oral cavity and when found, most commonly seen on the palate and the lower lip.^[9] WHO defines AML as “A frequently painful, benign subcutaneous or deep dermal tumor composed of mature smooth muscle bundles which are surrounded and interlaced by vascular channels”.^[5] The exact etiology of AML is unspecified. However, trauma, local infection, hormonal influences and arterio-­venous malformations are some of the possible causes.^[10] In our case, trauma was considered as an etiological factor.

Clinically it is very difficult to diagnose AML as it has no distinct features. One must rely on the histopathology which in itself is strenuous because of similarity with various other entities. It is believed that AML starts as an hemangioma, proceeds to form vascular leiomyoma and then ends up becoming a solid leiomyoma.^[11]

AMLs being spindle cell neoplasms, careful differentiation is critical from other spindle cell neoplasms such as neurofibroma, neurilemmoma, fibrous histiocytoma, solitary fibrous tumour. Neurofibroma has spindle cells with wavy nuclei and interlacing bundles, neurilemmoma shows Antoni A and Antoni B cell pattern. Apart from the histological differences, a negative S100 reaction ruled out the neural tumours. Furthermore, Fibrous histiocytoma has spindle cell proliferation with vesicular nuclei and the cells are arranged in a storiform pattern which is absent in AML. Solitary myofibroma can cause confusion where numerous proliferating fibroblasts and myofibroblasts are seen positive for SMA marker but the cells have tapered nuclei whereas in AML cigar shaped nuclei is present and desmin is positive in AML whereas it is negative in the former.^[4], ^[5]

Myopericytoma can also be confusing because AML and the latter share similar histologic features. Nonetheless, H-caldesmon is strongly positive in AML hence differentiating between the two lesions. H-caldesmon is a more specific immunohistochemical indicator for smooth muscle fibers than SMA.^[12]

Solitary Fibrous Tumour (SFT) was considered in our case since this tumour also has spindle cells arranged in pattern-less pattern around slit like blood vessels and has hypocellular & hypercellular areas as seen in the case of AML. Special stains like Masson Trichome, Van-Gieson along with immunostains such CD34, CD99 can help in clearing the dilemma between the two facsimileing tumours.^[13]

Angioleiomyomas are treated by surgical excision. Around 5% of the tumours show local recurrence owing to incomplete excision.^[10] There are no cases of malignant transformation reported in literature till now. Although angioleiomyosarcoma exists, hence one should be vigilant to differentiate between the benign AML and the malignant counterpart. Pathological features such as atypia, necrosis, pleomorphism, cellularity, and mitotic activity indicate a malignant tumour.^[14]

Conclusion

The diagnosis of histopathologically similar and uncommon benign tumours is crucial to avoid confusion with morphologically similar but more aggressive and histologically bland-appearing lesions. The presented case emphasizes the importance of histological and immunohistochemical examinations to arrive at the definitive diagnosis of rare tumours such as angiomyoma.

Source of Funding

None.

Conflict of Interest

None.