Solitary infantile myofibroma of the orbit

Abstract

Editor, An otherwise healthy 1-year-old girl developed proptosis of her left eye and swelling of the left superior eyelid over a period of a few months. There was no history of injury or genetic diseases in the family. Clinical examination revealed no signs of infection. Visual acuity and pupillar reflexes were normal in both eyes. A 3- mm ptosis of the left eyelid, restricted movements of the left eye in supero-temporal directions and increased retrobulbar resistance were present (Fig. 1A). Ophthalmoscopy of both eyes was normal. CT and MR scans (Fig. 1B, C) demonstrated a 2.3 × 1.0 mm large, homogeneous tumour in the lateral and superior parts of the left orbit. The tumour shadow did not involve the eyeball, but the lateral rectus muscle and the tear gland were hidden within the tumour signal. An anterior orbitotomy demonstrated a white, firm nonbleeding tumour. (A) Proptosis of the left eye and swelling of the left superior eyelid in a 1-year-old girl. (B) Computed tomography showing an isodense homogeneous tumour mass in the lateral and superior parts of the left orbit (arrow). (C) Magnetic resonance showing the isointense homogeneous tumour mass in the lateral and superior parts of the left orbit (arrow). (D) Microphotography showing delicate spindle-shaped and stellate irregular cells between strands of collagen fibrils. Haematoxylin and eosin. Bar = 25 μm. (E) The spindle cells are positive for anti-smooth muscle actin. Bar = 25 μm. A biopsy measuring 5 × 3 × 3 mm was achieved. Light microscopy of the tissue showed a biphasic appearance. In the periphery were strands of collagen fibrils among which delicate spindle-shaped and stellate irregular cells dominated (Fig. 1D). The nuclei were without nucleoli and had an evenly distributed chromatin. In the centre of the specimen, a few areas demonstrated more rounded and closely packed cells around vascular spaces in a haemangiopericytomatous fashion. There were no mitoses or foci of necrosis. Inflammatory cells were very sparse. The tear gland was intact in the specimen and was not invaded by the tumour. Immunohistochemistry showed a strong positivity with smooth muscle actin (Fig. 1E) and vimentin (Table 1). The morphology and immune reactivity indicated a solitary infantile myofibroma. Complete surgical removal of the tumour was performed through a trans-cranial orbitotomy. The child recovered well after surgery, and there have been no signs of recurrence. Solitary infantile myofibroma is a rare benign fibrous tumour most common in the head and neck in men (Chung & Enzinger 1981). The entity was first described by Stout (1954) and was renamed infantile myofibromatosis and divided into a solitary and multicentric type by Chung & Enzinger (1981). Eighty-nine per cent of the tumours develop during the first 2 years of life (Chung & Enzinger 1981). To our knowledge, 12 cases of solitary infantile myofibroma in the orbit have been described previously (Persaud et al. 2006; Rodrigues et al. 2006). Solitary myofibroma is usually a nontender and painless tumour, with or without orbital bone involvement, and can be rapidly progressing or slow growing (Chung & Enzinger 1981; Persaud et al. 2006; Rodrigues et al. 2006). The clinical and histopathological differential diagnoses of infantile myofibroma include solitary fibrous tumour, nodular fasciitis, fibrous histiocytoma, haemangiopericytoma, leiomyoma and leiomyosarcoma (Bernardini et al. 2003; Rodrigues et al. 2006). These conditions share a number of characteristics, but some immunohistological difference helps in the differential diagnosis. Solitary fibrous tumours are mostly CD34 positive (Bernardini et al. 2003) in contrast to infantile myofibroma. Leiomyoma and leiomyosarcoma show strong positivity for both smooth muscle actin and desmin (Bernardini et al. 2003), whereas infantile myofibroma shows negativity for desmin. Fibrous histiocytoma and infantile myofibroma differ in actin expression, i.e. infantile myofibroma is always highly reactive (Bernardini et al. 2003). The prognosis of solitary myofibroma is excellent, and complete excision is advised (Chung & Enzinger 1981; Persaud et al. 2006). This diagnosis should especially be considered in a child when encountering a painless solitary orbital tumour progressing over months. Malignant lesions of the orbit such as rhabdomyosarcoma and neuroblastoma should be suspected when rapid onset, progression and signs of inflammation are observed. Prompt biopsy to exclude these lesions should always be undertaken.