Chapter 12

Neuroradiology of Ocular and Orbital Tumors

J. Matthew Debnam

Abstract This chapter on neuroradiology for ophthalmologic tumors discusses the basic utilization of computed tomography and magnetic resonance imaging in the evaluation of lesions involving the globe and orbit. The protocol for these techniques, relevant imaging anatomy, and imaging features of the more common ophthalmologic tumors are discussed. The common radiographic features of ocular lesions, such as retinoblastoma, melanoma, and uveal metastases, as well as orbital lesions, including lymphoma, rhabdomysarcoma, nerve sheath tumors, fibrous lesions, and orbital pseudotumors are discussed. Lesions of the optic nerve, including glioma and meningioma, are also covered. The final section discusses radiographic findings for lesions of the lacrimal gland, secondary spread of tumors to the orbit and periocular region, and cutaneous lesions of the periocular region, including perineural tumor spread.

12.1 Introduction: Imaging and Protocol

Advances in computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography/computed tomography (PET/CT) have aided in the diagnosis of ocular and orbital lesions. Most orbital and some ocular lesions can be evaluated by CT imaging. CT is superior to MRI for evaluation of the bony structures around the orbit and detection of calcifications within lesions. CT is also used to exclude foreign bodies in preparation for MRI. With multidetector CT, imaging can be performed in the axial plane, and multiplanar reformatted images can be provided in any plane deemed necessary. However, because MRI provides exquisite soft tissue detail, it is the preferred imaging modality for some lesions of the orbit.

J.M. Debnam (B)

Section of Neuroradiology, Department of Radiology, The University of Texas M.D. Anderson Cancer Center, Houston, TX, USA

e-mail: matthew.debnam@mdanderson.org

Oncology Series 6, DOI 10.1007/978-1-4419-0374-7_12,

C Springer Science+Business Media, LLC 2011

The use of multiple pulse sequences provides different signal characteristics for the various types of orbital lesions, aiding in the differential diagnosis.

The MRI examination should be tailored to the patient’s specific symptom. Orbital imaging protocols generally include an axial T1 precontrast sequence, a T1 postcontrast sequence in three orthogonal planes, and an axial T2 sequence. Fat suppression technique may be employed on both T1 postcontrast and T2 sequences. Some institutions obtain at least one sequence without fat suppression because magnetic susceptibility, related to the patient’s makeup, dental amalgam, and braces, is increased with the fat suppression technique. For optic nerve lesions, obliquesagittal T1 postcontrast images along the optic nerve and coronal T2 images for comparison of the optic nerve size and signal intensity may be added. A 3-mm slice section thickness with a 0.5- to 1.0-mm gap between slices may be utilized for these sequences. An axial T1 postgadolinium sequence of the brain can also be added to assess for intracranial spread of orbital tumors and metastasis. An axial T2 sequence with fat saturation of the neck can be used to assess for associated lymphadenopathy.

The standard CT examination of the brain and orbits can be completed with the patient on the CT table for only a few minutes. The average MRI examination may take up to 1 hour. Administration of iodinated contrast material for CT or gadolinium for MRI is contraindicated in patients with renal failure. When intravenous contrast cannot be administered because of renal failure, a nephrologist should be consulted, as obtaining a diagnostic radiological study of the orbits without contrast is often of little benefit.

PET/CT involves the administration of 18F-fluorodeoxyglucose (FDG), which competes with serum glucose for uptake within the body. FDG accumulates in tumors, which have a high metabolic demand. In ophthalmic imaging, this modality may be used for both staging and assessing treatment response in lesions such as ocular adnexal lymphoma [1].

12.2 Anatomy

The bony anatomy of the orbit is well visualized with CT, especially utilizing bone windows. This includes the optic canal, lateral and medial orbital walls, superior and inferior orbital fissures, lacrimal fossa and nasolacrimal duct, and infraorbital canal. Coronal CT can be used to assess the orbital roof and floor (Fig. 12.13).

The extraocular muscles run parallel to the orbital walls. The medial and lateral rectus muscles are best visualized in the axial plane, while the superior and inferior rectus muscles are best visualized in the oblique sagittal plane. The levator palpebrae superioris muscle lies in close approximation to the superior rectus muscle and can be seen as a separate entity on oblique coronal imaging. The superior oblique muscle is best evaluated in the coronal plane and the inferior oblique muscle is best evaluated in the coronal, sagittal, or parasagittal plane. The trochlea, best seen in the axial plane, is often calcified and should not be misinterpreted as a foreign body. The