Contributed by Hong Wui Tan, MRCPath, Seng Geok Nicholas Goh, FRCPA, Wai Ming Yap, FRCPath, Khoon Leong Chuah, FRCPA
Department of Pathology, Singapore General Hospital, Outram Road, Singapore 169608, Republic of Singapore.
A 43 year old man presented 22 years ago with proptosis and reduced visual acuity of the right eye. He was investigated and found to have an orbital tumor which was subsequently biopsied but not resected. He currently presented with decreased visual acuity and impaired right-sided gaze. On imaging, there was a right retro-orbital tumor for which an excision was performed. Intraoperatively, a well-encapsulated tumor within the cystic component containing clear fluid was noted and the relation of this tumor to the nerve could not be clearly ascertained. On histology, the excised specimen revealed a cellular neoplasm consisting of sweeping fascicles of spindle cells with storiform appearance in some areas. Focal ill defined, Verocay body-like palisades were identified. Scattered blood vessels with hyalinised wall were noted. There was no necrosis, significant atypia or mitotic activity. The tumor showed strong staining for S-100 and focal staining for glial fibrillary acidic protein (GFAP) on immunohistochemistry and ultrastructurally, numerous intertwining cell processes were discerned. The findings corroborated a diagnosis of retrobulbar cellular schwannoma, the retrobulbar region being an uncommon location site for this tumor. Important differential diagnoses to be considered include meningioma, glial tumor in view of positive staining for GFAP in cellular schwannoma and malignant peripheral nerve sheath tumor (MPNST) in view of the increased cellularity. While metastases and death have not been described in cellular schwannoma, incompletely resected cellular schwannoma has presented with recurrence. In such a situation, mitotic count significantly correlates with the incidence of tumor recurrence and close follow up is recommended.
A 43 year old man presented 22 years ago with proptosis and reduced visual acuity of the right eye. He was investigated and found to have an orbital tumor which was subsequently biopsied but not resected. Post-operatively, he complained of decreased visual acuity. He currently complained of increasing impaired right-sided gaze and proptosis. Following the findings on imaging, a right panoramic frontal orbitotomy with orbital tumor excision was performed. Intraoperative findings disclosed a well-encapsulated tumor within the cystic component containing clear fluid. It was not possible to determine if the tumor was related to any nerve during the operative procedure.
Magnetic resonance imaging showed a 3.3 cm intraconal tumor within the right orbit (Fig. 1). The tumor involved the right optic nerve, extending posteriorly into the orbital apex and optic canal. It did not extend into the intracranial cavity or involve the extra-ocular muscles. Focal cystic areas were seen.
Grossly, the excised specimen consisted of multiple pieces of pale tan tissue altogether measuring 1.5 x 1 x 0.5cm which were completely submitted for histological examination. Additional fresh tissue available was used in the preparation of cytology smears and ultrastructural study.
Cytologic smears showed clusters and loose aggregates of ovoid to spindle cells with bland nuclei containing occasional small central nucleoli. The nuclei were randomly dispersed in an amorphous rounded masses formed by the abundant cytoplasm of each cell. The cytoplasm strung out in wispy strands between cell clusters (Fig. 2).
On light microscopy, the tumor was cellular, demonstrating sweeping fascicles of spindle cells with storiform appearance in some areas (Fig. 3). Focal ill defined, Verocay body-like palisades were seen (Fig. 4). Scattered blood vessels with hyalinised wall were noted. There was no necrosis, significant atypia or mitotic activity.
Immunohistochemistry revealed the spindle cells to be strongly positive for S100 protein (Fig. 5). Staining with glial fibrillary acidic protein (GFAP) was focally positive. The tumor cells were negative for CD34, smooth muscle actin (SMA), desmin, epithelial membrane antigen (EMA) and cytokeratin AE 1/3. The MIB-1 index was less than 3%. On electron microscopy, the predominant feature was that of numerous intertwining cell processes (Fig. 6).
No slide of the initial biopsy 22 years ago could be retrieved for review.