Other epithelial paranasal neoplasms that may invade the orbit but occur less frequently include adenoid cystic carcinoma and adenocarcinoma. Both are locally aggressive tumors characterized by a course of indolence, recurrence, and potential mortality.

Nonepithelial paranasal sinus tumors that may invade the orbit include a variety of benign and malignant entities. The most common of these are osteomas, fibrous dysplasia, and sarcomas, while osseous and cartilaginous tumors are rare. Osteoma is the most common of the nonepithelial paranasal sinus tumors; however, its pathogenesis remains unclear, though traumatic, infective, and hamartomatous theories have been proposed [20]. The fact that these tumors were found in 0.42% of plain sinus radiographs reflects their prevalence [22]. Osteomas are benign, slow-growing, well-circumscribed tumors composed of mature bone and can be completely excised in most cases. The most common site of origin is the frontal sinus.

6.3 Tumors of Brain Origin

Meningiomas are the most common intracranial tumor to extend to the orbit, and invasion by any other intracranial tumor is exceedingly rare [17].

6.3.1 Meningioma

Intracranial meningiomas that secondarily invade the orbit are much more common than primary orbital meningiomas. Meningiomas are invasive tumors that arise from arachnoid villi. They commonly (in 18–20% of cases) arise from the dura of the sphenoid wing (i.e., ridge, planum, parasellar region, or optic canal) and may extend into the orbit through bone, the superior orbital fissure, or the optic canal (Fig. 6.4) [17, 23]. Tumor invasion may thus compress the optic nerve or superior orbital fissure. These sphenoid wing meningiomas occur three times more often in women, typically during their fifth decade [22]. Tumors occurring in young patients tend to be more aggressive. Multifocal simultaneous meningiomas may occur, and there is an increased frequency of intracranial and orbital meningiomas in patients with neurofibromatosis type 2 (12% of patients) [22].

Ophthalmic manifestations are dependent on the location of the primary tumor. Medially located meningiomas arising near the sella and optic nerves cause early optic nerve and cavernous sinus compression leading to visual defects, motor and sensory deficits, venous obstructive signs such as edema and chemosis, and papilledema or optic atrophy [23, 24]. Tumors arising near the lateral third of the sphenoid bone, middle cranial fossa, and olfactory groove often produce a temporal fossa mass, chronic proptosis, ophthalmoplegia, and late optic nerve compression [24]. A classic finding in laterally located tumors is fullness in the temporal fossa due to reactive bone thickening (hyperostosis). This may be easily noted in patients

Fig. 6.4 Computed tomography image of a left middle cranial fossa meningioma invading the posterior orbital apex

wearing glasses, as the gap between the temporalis and the temple of the glasses is narrow compared to the gap on the contralateral side. Retrospective review of photographs can also be helpful in this regard. Olfactory groove meningiomas may cause loss of the sense of smell, along with compressive optic neuropathy [24]. Rarely, lower eyelid edema or erythema and chemosis may be present. Overall, half of patients present with progressive unilateral visual loss and half with progressive bilateral visual loss. The exception to this pattern is patients with olfactory groove meningiomas, who have a higher incidence of bilateral visual loss [22].

Computed tomography commonly reveals localized hyperostosis with associated calcifications owing to psammoma bodies in the tumor [25]. At times, bone absorption and destruction are apparent. Magnetic resonance imaging with contrast enhancement can help outline the extent of tumor adjacent to the bone and may prove superior in detecting smaller tumors. The lesion is usually well defined, homogeneous, and characteristically of increased density with uniform postcontrast enhancement [22].

The development of multidisciplinary and microsurgical approaches has substantially improved surgical outcomes for intracranial meningiomas with secondary orbital involvement. Provided the tumor is well defined, excision is very effective. However, invasion of bone and adjacent soft tissues or encasement of vital structures may preclude complete excision. Treatment consists of combined neurosurgical and orbital panoramic orbitotomies with excision or debulking in tandem with postoperative radiation therapy as an adjunct or in cases of incomplete excision, recurrent tumors, or cavernous sinus lesions [22, 26, 27]. Major debulking can be effective in improving cosmesis and alleviating compressive symptoms, leading to reversal or postponement of visual loss [22]. Adjuvant radiation therapy has been proven to reduce overall time to and rates of recurrence [22]. Image-guided techniques may play a role in the future surgical or stereotactic radiosurgical treatment of meningiomas [22, 28]. Because recurrence rates are significant, long-term follow-up of surgical patients is key.