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Neuroradiology Case of the Week

Case 173

Loris Cedeno MD, Ravinder Sidhu, MD,
and Per-Lennart Westesson, MD, PhD, DDS

Clinical Presentation: This is a 19-year-old female diagnosed with Langerhan's cell histiocytosis in 1987 and optic neuropathy.

Radiological Findings: There is an ovoid moderately to strongly enhancing lesion in the right orbital apex (Fig. 1). The lesion measures 1.8 cm x 2.0 cm x 1.5 cm.  The lesion has intermediate T1 (not shown) and slightly high T2 signal intensity and demonstrates mass effect on the rectus muscles, as well as compression and superior medial displacement of the right optic nerve. Increased fluid is also seen in the distal optic nerve between the tumor and the globe (Fig. 2). Mild hyperintense signal is seen within the optic nerve in the STIR images(Figs. 3&4).

Diagnosis: Fibroblastic meningioma, biopsy proven

Differential Diagnosis:

• Optic neuritis
• Orbital sarcoidosis
• Optic nerve glioma
• Lymphoma and metastasis
• Orbital pseudotumor

Discussion: Orbital meningiomas are defined as benign slow growing neoplasms of the intraorbital optic nerve dural sheath. They tend to present early as they can be symptomatic despite their small size. They can have a tubular, pedunculated or fusiform shape, with tubular being the most common. Characteristic linear or punctuate calcifications are seen on CT in 30% to 50% of patients. It typically spares the distal optic nerve sheath as it enters the optic nerve head. On MRI, tumors tend to demonstrate moderate to marked uniform enhancement. These tumors have variable signal on T2 weighted images and can be hyperintense to hypointense. T2 can also show perioptic cysts which a specific feature for these lesions. This is well illustrated in our patient where increased fluid is seen surrounding the distal optic nerve between the tumor and the globe.
      Orbital meningiomas can be classified as primary or secondary depending on there site of origin. They are considered primary tumors if they arise from the optic sheath itself and more commonly secondary, if they extend into the orbit from the intracranial meninges. In fact, about 90% are secondary lesions rather than primary. Primary optic nerve sheath meningiomas arise from the cap cells of the arachnoid surrounding the intraorbital or, less frequently, the intracanalicular optic nerve. They are found more commonly in women than men. Complications include blindness secondary to optic nerve compression. Although benign, these tumors can have a more aggressive behavior in juvenile patients. Stereotactic radiosurgery is currently considered the treatment of choice for patients with preservable vision. Surgical excision is indicated for tumor control if there is intracranial extension or if vision preservation is not possible. Vision preservation is most difficult with circumferential tumors.

References:

1. Liu JK, Forman S, Hershewe GL, Moorthy CR, Benzil DL: Optic nerve sheath meningiomas: visual improvement after stereotactic radiotherapy. Neurosurgery 2002 May; 50(5):950-5. [Medline]
2. Harnsberger, HR, et al. Diagnostic Imaging: Head and Neck. W.B. Saunders, 2004; II,1 46-49.
3. Khoromi S, Zacariah SB: Meningioma, Optic Nerve Sheath. http://www.emedicine.com/oph/topic671.htm