Ancient schwannoma of the orbit.

The ancient schwannoma is a rare variant of a neurilemoma with a course typical of a slow-growing benign neoplasm. Histologically, it can be confused with a malignant mesenchymal tumor because of increased cellularity, nuclear pleomorphism, and hyperchromatism. Despite the degree of nuclear atypia, mitotic figures are absent. We describe the clinical and histopathologic features of an ancient schwannoma of the orbit. A need for early removal of such tumors is recommended to prevent complications.

Introduction

Schwannomas of the orbit are rare and account for only 1-6% of all orbital tumors.[1] In the orbit, schwannomas are usually unilateral and may arise from the supraorbital, infraorbital, supratrochlear, ciliary, oculomotor, trochlear, or abducens nerves. The variable presentation and location of this tumor can certainly make the diagnosis difficult, which usually is confirmed by histopathological examination. The ancient schwannoma is a rare histological variant of a neurilemoma derived from the neural sheath of Schwann. In 1951, Ackerman and Taylor[2] reported 10 neurogenic tumors of the thorax that showed microscopic features typical of schwannomas but that were distinctive because of hypercellular areas with nuclear pleomorphism and hyperchromatism suggesting fibrosarcoma, as well as hypocellular areas with considerable fibrosis. The clinical course, however, was benign in all cases during a mean follow-up period of three and half years. They interpreted these findings as degenerative changes indicative of long duration and thus designated the tumors ancient schwannomas. Since that first report, several authors have described ancient schwannomas in a variety of locations in the head and neck,[3] We could find few references illustrating orbital ancient schwannoma. Imaging modalities are non-specific for schwannomas, but can define tumor size, site and extension. The mainstay treatment is complete excision, although local recurrence may occur in large and incompletely excised lesions. Malignant change is exceedingly rare.[4]

Case Report

A 68-year old woman with chief complaints of gradual protrusion followed by pain, redness, and watering in the eye since five years. She had no history of trauma, headache, giddiness, convulsion, no history suggestive of blood dyscrasias. There was history of hypertension but well controlled by medications. Personal history and family history was not contributory. On examination, no systemic abnormality was detected. Local examination revealed left eye proptosis 25 millimeter showing downward and forward displacement giving the appearance of hypotropia. Interpalpabral fissure was increased. There was restriction of abduction. On palpation, 4 × 3 centimeter soft swelling was palpated. Finger insulation test could be performed indicating that the orbital margins were free from mass. Vision was 6/60 left eye. Fundus showed nuclear sclerosis grade I, disc, blood vessels showed arteriolar attenuation and foveal reflex was healthy. All routine hematological investigations were within normal range.

Contrast enhanced computerised tomograph (CECT) of brain and orbit demonstrated a mass of size 4.5 × 2.6 × 2.7 cm placed superiorly in the left orbit. This mass was causing proptosis of the left eye globe along with medial displacement of superior ophthalmic vein and inferior displacement of superior rectus muscle thus causing scalloping and thinning of floor of the frontal sinus as well as the roof and lateral of orbit. No evidence of calcification was seen within the swelling.

The clinical diagnosis was cavernous hemangioma. Hemangiopericytoma and soft tissue tumor was considered less likely diagnostic possibilities.

A left lateral orbitotomy was performed through an extended eyelid crease incision. The mass was gray, smooth, and well encapsulated. The mass was removed in its entirety without violation of its capsule.

Follow up found that the patient is alright with good vision after one month of operation.

Excised mass was sent for histopathogical confirmation.

Pathological findings: Gross- received mass of size 3 × 2 cm, which is well circumscribed, on cut section mass was avascular smooth, partly grayish white, and partly yellowish.

Microscopically, a biphasic pattern of tumor cells was seen with areas of closely packed spindle cells having fusiform nuclei and eosinophilic cytoplasm (Antoni A) admixed with looser myxoid tissue having ovoid cells (Antoni B) [Figure 1]. At places, these tumor cells were arranged in palisades and this arrangement of cells is referred to as Verocay bodies. Nuclear atypia was not seen. Also seen are many macrophages and areas of hemorrhages [Figure 2]. The diagnosis was peripheral nerve sheath tumor with ancient features and confirmed by immunohistochemistry; the results are positive for vimentin, neuron-specificenolase, and S-100 protein Figure 3 and negative for cytokeratin.

Figure 1

Photomicrograph showing areas of Antoni A and Antoni B pattern, H/E ×20

Figure 2

Photomicrograph showing macrophages and areas of hemorrhage, H/E ×20

Figure 3

Photomicrograph showing S-100 positivity

Discussion

Ancient schwannoma of orbit is rare. Schwannomas are found in all age groups but are more common in the first four decades and affect both sexes equally. They may occur in association with neurofibromatosis or arise sporadically.[5]

The histopathologic features of ancient schwannoma are characterized by areas of increased cellularity with nuclear pleomorphism and hyperchromatism, areas of hypocellularity, and considerable fibrosis with focal hyalinization. Micro cystic degeneration, hemorrhage with hemosiderin-laden macrophages, lipid-filled foam cells, and focal calcification also may be seen.[6] The cellular changes can make accurate pathological diagnosis difficult. Increased cellularity and nuclear atypia may lead to the erroneous interpretation of malignant tumor. Dahl[7] reported 6 of 11 cases of ancient schwannoma that were originally misdiagnosed as malignant tumors, such as neurofibrosarcoma or malignant schwannoma. Certain histological features can assist in the differentiation of ancient schwannomas from malignant tumors.[2] These include the lack of mitoses, evidence of hemorrhage, areas of degeneration with hyalinization, and the presence of a histological capsule. Immunohistochemical testing can aid the identification of neural sheath derived tumors; the results are positive for vimentin, neuron-specificenolase, and S-100 protein, and negative for cytokeratin. Malignant schwannomas are exceedingly rare in the orbit.[5] Some forms of malignant schwannoma exhibiting so-called Schwann cell differentiation with densely packed, often palisading, short spindle cells may resemble ancient schwannoma. These malignant schwannomas, however, show mitoses and infiltrative growth, distinguishing them from ancient schwannomas.[456] Malignant changes of benign schwannomas have been reported rarely.[6] Schwannomas are less likely than neurofibromas to undergo malignant change.[6] The diagnosis of malignant change of benign schwannoma requires the following criteria: (1) demonstrable areas of benign schwannoma (2) unequivocal malignant foci manifested by increased cellularity, numerous mitoses, anaplastic cells, and invasiveness (3) transitional areas between malignant and benign regions.

Surgical excision is the treatment of choice and the tumor should be removed intact at the earliest to prevent compression of the optic nerve.[8] If a schwannoma is managed properly by complete surgical excision of tumor, its prognosis is good and recurrence is not seen.