Intraosseous solitary myofibroma of the orbit in an adolescent woman

Abstract

A 16-year-old woman presented with a painless, progressive, hard swelling in the left inferolateral orbital wall for the past 1 year. There was no diminution of vision or limitation of ocular motility. Imaging revealed an intraosseous, well-defined, expansile, soft tissue lesion in the inferolateral wall of the left orbit. A left anterior orbitotomy with complete surgical excision was performed. Histopathological evaluation of the specimen revealed fascicular pattern of spindle cells with a rich network of slit-like, branching blood vessels. Tumour cells exhibited smooth muscle actin and vimentin positivity but were negative for CD-34 and STAT-6. In absence of any systemic manifestation, a diagnosis of intraosseous solitary orbital myofibroma was made. The case highlights the importance of integrating clinical, radiological and histopathological features in overcoming the diagnostic challenge of differentiating myofibroma from other mesenchymal neoplasms. It also brings forth the importance of complete resection and curettage to prevent recurrence.

Background

Myofibroma, a spindle-cell neoplasm, closely resembles other mesenchymal tumours, posing a diagnostic challenge.¹ It may manifest as a solitary mass, have a multicentric involvement or can be generalised, with multifocal and visceral disturbances.² The solitary form generally presents as a unilateral, gradually progressive, painless mass during infancy or childhood. In the orbit, the mass is usually extraosseous in location and may be associated with bony involvement.^{3 4}

Herein, we describe a rare case of an intraosseous solitary myofibroma of the orbit occurring in an adolescent female. The report showcases the importance of imaging and Immunohistochemistry (IHC) in the diagnosis and management of this rare tumour.

Case presentation

A 16-year-old woman presented with a gradually progressive, painless mass in the inferolateral orbital wall for the past 1 year. There was no history of trauma or any systemic illness. No significant birth or family history could be elicited. On examination, the visual acuity was 20/20 and the anterior segment, pupillary reaction and funduscopy of both the eyes was within normal limits. A well-defined, non-tender, immobile mass was palpable in the inferolateral aspect of the left orbit. The mass was hard in consistency and appeared fixed to the underlying bone with no overlying skin changes. There was a vertical and horizontal dystopia of 2 mm, displacing the left globe superomedially (figure 1). The swelling was transillumination-negative and did not demonstrate any change in size with Valsalva manoeuvre. There was no evidence of proptosis, limitation of extraocular muscle movements or lymphadenopathy.

Figure 1.

Clinical photograph showing (A) swelling over the lateral aspect of the left lower lid causing superomedial displacement of the globe (B) oblique view.

Investigations and treatment

A non-contrast CT scan of the orbit revealed a well-circumscribed, intraosseous, spherical, expansile lesion, measuring 2.6×1.7×1.5 cm, in the inferolateral wall (zygomatic bone) of the left orbit, associated with severe thinning of the expanded cortices. The heterogeneous lesion exhibited soft tissue attenuation and exerted mass effect over the adjacent globe (figure 2).

Figure 2.

CT scan orbit (A) axial view (B) coronal view, showing an intraosseous, soft tissue mass in the left zygomatic bone (arrows), abutting the globe.

Due to the intraosseous location, fine-needle aspiration cytology could not be performed, and an excision biopsy was planned. Through a transcutaneous approach, deroofing of the bony wall surrounding the mass was done using an electric saw. The mass was extricated using a periosteum elevator and bone curette, and removed in-toto. On gross examination, a well-circumscribed, reddish-grey mass, measuring, 3.2×1.5×1 cm, was seen (figure 3). The histopathological evaluation of the excised specimen revealed a well-circumscribed, spindle cell tumour with variable cellularity, nearly replacing the cancellous bone. Periosteum, occasional bony spicules and periorbital fat were noted in the outer area. Short fascicles of spindle-shaped cells exhibiting moderate eosinophilic cytoplasm, regular nuclei and inconspicuous nucleoli, with numerous thin-walled, slit-like, branching blood vessels dispersed in the sparse collagenous stroma were seen. Occasional multinucleated giant cells were noted in the peripheral area. No evidence of mitosis, necrosis, atypia or pleomorphism was found (figure 4). On IHC staining, tumour fascicles demonstrated positivity for smooth muscle actin (SMA) and vimentin, and were negative for desmin, H-caldesmon, epithelial membrane antigen, beta-catenin, S-100, anaplastic lymphoma kinase 1 (ALK-1) and STAT 6 (figure 5). CD-34 marker highlighted the vascular endothelial cells but stained negative for tumour cells.

Figure 3.

Gross examination of the excised specimen, revealing a well-circumscribed, reddish-grey mass.

Figure 4.

Histopathological examination of the specimen, H&E stain, (A) ×10, showing a well-circumscribed spindle cell tumour with variable cellularity (white arrow). The bony spicules (black arrow) are noted in the periphery. (B) ×40, showing short fascicles of spindle cells, devoid of atypia, pleomorphism or mitosis, along with numerous slit-like blood vessels. (C) ×40, showing numerous branching, staghorn-like vessels (arrow), along with spindle cells. (D) ×20, showing occasional multinucleated giant cells in the peripheral region (arrow).

Figure 5.

Immunohistochemistry (A) ×20, revealing dense cytoplasmic smooth muscle actin positivity for tumour cells. The smooth muscle cells of the blood vessels are acting as an internal control (arrow). (B) ×10, depicting negative staining for STAT-6.

No multicentric or visceral involvement was found on performing a comprehensive clinical examination along with CT scan chest, abdomen and pelvis. Thus, a definitive diagnosis of an intraosseous solitary orbital myofibroma was made.

Outcome and follow-up

The patient underwent an uneventful recovery and achieved satisfactory functional and cosmetic outcomes. Postoperatively, no limitation of extraocular movements was observed. A repeat orbital CT scan at 3 years following excision did not show any recurrence or evidence of residual disease (figure 6).

Figure 6.

(A) Clinical photographs showing complete resolution of the swelling following surgery and normal extraocular movements in all gazes. (B) Contrast-enhanced CT scan orbit, axial view, soft tissue window and (C) coronal section, bone window, revealing complete resolution of the lesion with mild bony remodelling and expanded cortex at the site of surgery. No evidence of soft tissue lesion is seen.

Discussion

Myofibroma is a benign mesenchymal neoplasm which most commonly affects head and neck, trunk and extremities of the body.^{1 5} Isolated orbital involvement is uncommon in occurrence, with only a few cases reported until.^{3 4}

The multifocal disease, also referred to as myofibromatosis, usually affects females, and shows a dominant pattern of inheritance. It is associated with a poorer prognosis and higher risk of mortality. On the contrary, solitary myofibroma usually manifests sporadically and exhibits a favourable prognosis.^{6 7}

Although the exact etiopathogenesis of a solitary orbital myofibroma is unknown, one third of these cases are congenital. In some cases, trauma has been implicated as the provoking agent.⁵ In our patient, none of these factors could be recognised. The basis for predilection of these tumours for the left side of the orbit, as also seen in this case, is yet to be identified.⁷

In the orbit, solitary myofibroma most commonly manifests as a unilateral, gradually progressive mass which may be associated with adjacent bony erosion, bone remodelling or bone defect.^{3 8 9} Intraosseous myofibroma may possess ill-defined margins, simulating a malignancy.³ In our patient though the mass was intraosseous, the margins were well defined and there was thinning of the adjacent bone.

In view of the CT scan findings and clinical features, the differential diagnosis included benign disorders such as fibrous histiocytoma, solitary fibrous tumour (SFT), Langerhans cell histiocytosis, fibro-osseous lesions like non-ossifying fibroma (NOF) and fibrous dysplasia of the orbit, schwannoma and neurofibroma. Additionally, owing to the bony hard consistency, the intraosseous nature of the mass and presentation at a young age, malignant lesions such as fibrosarcoma, Ewing’s sarcoma and osteosarcoma were also kept as a possibility. Following the availability of histopathological report, the presence of the short fascicles of spindle cells, devoid of atypia, mitosis, inflammation or pleomorphism, along with an abundant network of staghorn-like, branching blood vessels, ruled out malignancy. Based on the histopathology, the differential diagnoses narrowed down to solitary myofibroma, SFT, vascular variant of leiomyoma, NOF and nodular fasciitis. Thereafter, IHC staining was performed which was positive for SMA and vimentin and negative for desmin, CD-34, S-100, ALK-1, H-caldesmon and STAT-6. This confirmed the myofibroblastic nature of the tumour, clinching the diagnosis of a solitary orbital myofibroma.

SFT, an important diagnostic consideration in this case owing to similar histopathological findings, was ruled out based on negative staining of tumour cells with both, CD-34 and STAT 6.^{10 11}

Vascular leiomyoma is represented by dilated sinusoidal capillaries and shows concentric layering of vascular smooth muscles around the blood vessels, which differed from our histopathological findings. These tumours reveal intense immunostaining for SMA as well as positivity for desmin, vimentin, CD-34 and CD-31.^{12 13} Moreover, unlike a solitary myofibroma which may occasionally harbour multinucleated giant cells, these have never been described in case of leiomyoma.⁷

NOF is histologically characterised by a storiform pattern of fibroblast-like spindle cells, intermixed with xanthoma cells, multinucleated giant cells and lymphocytes, and thus, did not qualify as our primary diagnosis. Furthermore, this benign, fibrohistiocytic proliferative tumour usually affects the long bones, and rarely the mandible and maxilla.¹⁴ Nodular fasciitis was ruled out due to absence of inflammatory infiltrates and the intraosseous location.6 7 15–17

It was only after correlating the clinical features, the distinctive intraosseous location, and the histopathological features, that a plausible diagnosis of solitary myofibroma could be made.

Although a few studies recommend a conservative approach on the grounds of spontaneous resolution seen in some cases, surgical excision remains the first line of management in case of a solitary orbital myofibroma.¹⁸ Attempt should be made to excise the lesion in-toto, as was done in this patient, to minimise recurrence.^{3 19} Although the recurrence rate is less than 10% after excision, the tumour has been shown to recur as late as 6 months following surgical intervention, thus warranting a close follow- up.⁷ For intraosseous tumours, additional bone curettage may be required, as was performed in our case, and there was no recurrence in the 3 years of follow-up.

As rare is the occurrence of solitary myofibroma in the orbit, rarer is its presentation in adulthood with only three cases reported in the literature until.^20–22 To the best of our knowledge, our case is the first report of an intraosseous solitary orbital myofibroma in a patient over the age of 12 years (table 1).

Table 1.

A review of cases of solitary orbital myofibroma in adolescence and adulthood

Author	Age/ sex	Presenting sign	Duration	Site	Imaging	Histology	T/t	Outcome (follow-up)
Servat20	47 yrs/F	Painful proptosis, diminution of vision	10 months	Right orbito cranial	Osteolytic lesion with expansion of adjacent bone, extending into frontal sinus and frontal lobe	Mixture of spindle and epithelioid cells IHC—vimentin and SMA positivity	Surgical excision	No recurrence, (11 months)
Hemlatha et al	26 yrs/F	Bilateral microphthalmia with left LL nodular swelling	Not mentioned	Left orbit	Not mentioned	Biphasic pattern, peripheral myofibroblastic and central hemangio—pericytoma-like pattern. Focal areas of adipose tissue. IHC—vimentin positivity	Surgical excision	Not mentioned
Morrow22	24 yrs/F	Left eyelid swelling	6 months	Left orbit	Extraosseous, extraconal mass in the superior aspect of left orbit	Spindle cell neoplasm IHC—desmin and SMA positivity	Surgical excision	Not mentioned
Our case	16 yrs/F	Left LL swelling	2 years	Left orbit	Intraosseous, heterogeneous spherical expansile lesion in the zygomatic bone (inferolateral wall) of the left orbit	Spindle cell neoplasm with branching vessels, few giant cells, bony spicules, and periorbital fat seen in the periphery. IHC—SMA and vimentin positivity	Surgical excision	No recurrence, (36 months)

F, female; IHC, immunohistochemistry; LL, lower lid; SMA, smooth muscle actin; T/t, treatment.;

To conclude, intraosseous solitary orbital myofibroma can occur beyond infancy and childhood and must be considered as an important diagnostic consideration in any case of a well-defined solitary orbital mass. A stepwise, integrated approach is crucial in diagnosis and appropriate management. The clinician must be mindful of possibility of recurrence or subsequent visceral and multicentric involvement, highlighting the need for a long-term follow-up.

Patient’s perspective.

I had a large swelling on face below the left eye for 1 year. It did not look good so I avoided going out. I then underwent surgery and the swelling disappeared. Thankfully, doctors told me it was not cancer. I have regained my confidence now and I am happy.

Learning points.

• Solitary myofibroma should be considered as a differential diagnosis in any case of a well-defined orbital mass.

• For a definitive diagnosis of rare tumours like solitary myofibroma, correlation of clinical, radiological and histopathological features, including detailed immunohistochemistry, is required.

• Meticulous surgical excision with bony curettage prevents recurrence.

Ethics statements

Patient consent for publication

Consent obtained from parent(s)/guardian(s).