and are associated with neurofibromatosis type 2 [33]. Optic nerve sheath meningiomas demonstrate a tubular configuration or may grow eccentrically over the optic nerve. On CT, the lesion is hyperdense, with intensely enhancing linear bands seen around the nerve. Calcification is frequent and highly suggestive of meningioma. On MRI, the soft tissue mass surrounding the optic nerve is hypointense to isointense to brain on T1 and T2 images. Some lesions have cystic components. The tumor shows marked enhancement around the optic nerve, resulting in linear enhancement along the course of the optic nerve in the axial plane (the so-called railroad track or tram track sign), and a rim-like appearance around the nerve in the coronal plane (Fig. 12.11). This enhancement pattern may differentiate meningioma from optic nerve glioma. Orbital meningiomas can also occur that primarily involve the greater wing of the sphenoid (Fig. 12.12), causing proptosis and visual loss.

Fig. 12.11 Optic nerve meningioma, left optic nerve. (a) Axial T1 postcontrast image demonstrates enhancement of the mass parallel to the left optic nerve (arrows), the so-called tram track appearance. (b) Coronal T1 postcontrast image shows circumferential enhancement around the left optic nerve (arrow)

12.6 Lacrimal Gland Tumors

Fifty percent of lacrimal gland lesions are epithelial tumors, with the rest being lymphoma or inflammatory processes [34]. Metastasis to the lacrimal gland is rare [34]. Half of epithelial lacrimal gland tumors are pleomorphic adenoma (benign mixed), and half are malignant, with adenoid cystic carcinoma of the lacrimal gland being the most common. Benign tumors are often smooth with well-defined margins (Fig. 12.13), while malignant lesions have irregular margins, suggestive of infiltration, and may have associated perineural spread (Fig. 12.14) [35]. Benign or slow

Fig. 12.12 Recurrent meningioma, left sphenoid wing. Axial T1 postcontrast image shows a mass involving the left sphenoid bone and infratemporal fossa, with intraorbital extension, compression upon the globe and proptosis (arrows)

Fig. 12.13 Pleomorphic adenoma, right lacrimal gland. (a) Coronal postcontrast, soft tissue window, CT soft tissue window demonstrates a well-defined mass involving the superior orbit with inferior displacement of the globe and remodeling of the lacrimal gland bony fossa. (b) Coronal CT, bone window, demonstrates bony remodeling of the orbital roof (arrow)

growing lacrimal gland tumors are associated with bony remodeling of the walls of the lacrimal gland fossa whereas malignant processes are more likely to cause bony erosion. Neoplastic lesions rarely arise in the anterior aspect of the lacrimal gland and tend to grow posteriorly. Epithelial lesions may indent the globe [35] and may produce bone changes [34]. Lymphoid tumors show diffuse enlargement with a pancake-like spread and frequently have anterior and posterior extensions.

Fig. 12.15 Adenoid cystic carcinoma, left maxillary sinus. (a) Axial postcontrast CT image demonstrates a mass involving the left orbit, periorbital soft tissue, and pterygopalatine fossa (large arrows). Note the normal right pterygopalatine fossa (small arrow). (b) Coronal postcontrast CT image shows an invasive left maxillary sinus mass with destruction of the orbital floor (arrows)

as meningioma and glioblastoma, can grow into the orbit through the superior and posterior walls, superior orbital fissure, and optic canal. Skin cancers and lesions of subcutaneous soft tissue can grow into the preseptal space and directly invade the orbit. Lesions such as adenoid cystic carcinoma of the oral and sinonasal cavities can also extend into the pterygopalatine fossa, through the inferior orbital fissure, and then into the orbit, either by direct extension or by perineural spread.

12.8 Periorbital Skin Cancer and Perineural Spread

Tumors of the skin, including basal cell carcinoma, squamous cell carcinoma, and melanoma, can appear as an exophytic mass (Fig. 12.16) of the periorbital soft tissues or invade deep into the subcutaneous soft tissue. These lesions can also extend along the first and second divisions of the trigeminal nerve.

Skin cancers involving the forehead, upper eyelid, and scalp may spread along distal branches of the frontal nerve, a component of the ophthalmic division of the trigeminal nerve (V1). Perineural spread may extend along these nerves in the orbital roof (Fig. 12.17), through the superior orbital fissure, and into the cavernous sinus.

Lesions of the temporal region and lateral cheek may extend in a retrograde fashion along the zygomatic nerve, a branch of the maxillary division of the trigeminal nerve (V2). The nerve extends along the lateral orbital wall, through the inferior orbital fissure, and into the pterygopalatine fossa. Perineural tumor spread of lesions

Fig. 12.16 Melanoma, left eyelid. Axial T1 postcontrast image demonstrates an exophytic lesion arising on the left eyelid (arrow)

Fig. 12.17 Squamous cell carcinoma, left forehead. Coronal T1 postcontrast image demonstrates perineural spread along the first division of the left trigeminal nerve (V1) (arrow)

involving the nose, midface, and cheek may occur along the infraorbital nerve. The nerve extends through the infraorbital foramen, traveling along the floor of the orbit (Fig. 12.18), through the inferior orbital fissure, and into the pterygopalatine fossa. From the pterygopalatine fossa, lesions may extend in an antegrade fashion along other branches or in a retrograde fashion through the foramen rotundum to the cavernous sinus.