Orbit MRI

Optic nerve and nerve sheath tumors

Pathologies of the optic nerve-sheath complex require careful differential diagnosis. The imaging appearance allows for distinguishing between the two most common nosologies:

• Optic nerve glioma (Optic Nerve Glioma). Typical for children in the first decade of life. Histologically, this is usually a pilocytic astrocytoma (WHO grade 1) with slow growth. Rare forms in adults can be anaplastic or glioblastoma multiforme (WHO grade 3–4) with an aggressive course. On MRI, the tumor shows an iso- or hypointense signal on T1-weighted images and a hyperintense signal on T2-weighted images, causing fusiform thickening of the nervus opticus and widening of the optic canal (canalis opticus). The optic chiasm (chiasma opticum) may be involved in the process.
• Optic nerve sheath meningioma. More common in middle-aged women. The primary form originates from the arachnoid mater of the nerve, while the secondary form invades the orbit from the sphenoid wing. It forms a circular or fusiform thickening. A classic MRI sign is the tram-track sign (tram-track sign), where contrast enhancement accumulates peripherally around the unchanged nerve. Bilateral lesions are characteristic of neurofibromatosis type 2 (NF2). On CT, calcifications are frequently found within the tumor tissue (20–50%), which is atypical for gliomas.

Vascular and neural masses

Cavernous hemangioma — the most common primary orbital tumor in adult patients. Morphologically, this is not a true neoplasm, but an angiographically "silent" venous malformation with a fibrous pseudocapsule containing phleboliths.

Most frequently, it is located within the extraocular muscle cone (intraconal). Clinically, it manifests as slowly progressive exophthalmos and diplopia. On MRI, the mass is hypointense on T1-weighted images and hyperintense on T2-weighted images. The most specific diagnostic feature upon gadolinium administration is progressive centripetal filling, which starts from a small point or an individual fragment of the node.

Nerve sheath tumors (schwannomas, neurofibromas) may be located at the orbital apex, demonstrating heterogeneous or intense homogeneous contrast enhancement. They are capable of causing bone remodeling and extending into the cranial cavity through the superior orbital fissure (fissura orbitalis superior).

Infiltrative and inflammatory processes

Systemic diseases can mimic neoplastic growth, affecting the structures of the orbital apex, glands, and sheaths.

1. Orbital sarcoidosis. Characterized by a hyperintense MR signal on STIR imaging and active contrast enhancement at the orbital apex. Sarcoid perineuritis visually forms "tram tracks", requiring differentiation from meningioma. The pathology often extends through the fissura orbitalis superior and the optic canal, causing extensive dural thickening of the convexity surface. Bilateral enlargement of the lacrimal glands (glandula lacrimalis) leading to exophthalmos is also possible.
2. Orbital lymphoma. Capable of diffusely affecting tissues, including the lacrimal gland. On tomograms, it appears as a homogeneously enhancing mass, typically characterized by restricted diffusion on DWI and ADC maps.

Class and exam questions

What else to study on this topic

• The role of pulse sequences: the use of STIR and fat-suppressed modes in neuroimaging.
• Differential diagnosis of lacrimal gland mass lesions on MRI.
• Assessment of the extension of orbital pathologies through the superior orbital fissure into the cranial cavity.
• Features of orbital bone remodeling in nerve sheath tumors.
• Rare malignant optic nerve gliomas in adult patients: histology and prognosis.

Other topics in the Neuroimaging section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.