Question

A patient presents with progressive painless proptosis of the left eye. Enumerate the various pathologies that can cause proptosis, with respect to different compartments of the orbit on imaging. Discuss the imaging features of pathologies affecting the intra-conal compartment of the orbit. [3+7]

Hint:

Imaging of intra-conal orbital pathologies often requires MRI for its superior soft tissue contrast and ability to delineate soft tissue lesions, vascular structures, and the relationship of masses to the optic nerve and ocular muscles.

Answer 1

Step 1: Pathologies that Can Cause Proptosis and Their Relation to Different Compartments of the Orbit.
Proptosis (or exophthalmos) refers to the abnormal protrusion of the eye, which can be caused by various pathologies affecting different compartments of the orbit. The orbit is anatomically divided into the following compartments: 1. Preseptal Compartment (Anterior Compartment): - Infections such as cellulitis or abscess (e.g., orbital cellulitis). - Inflammatory conditions like thyroid eye disease (Graves' orbitopathy). - Trauma leading to orbital hematomas or fractures. 2. Postseptal Compartment (Posterior Compartment): - Tumors: Both benign (e.g., meningioma, optic nerve gliom and malignant (e.g., lymphoma, metastatic tumors). - Vascular malformations: Carotid-cavernous fistula, vascular tumors. - Infections that spread from the paranasal sinuses into the orbit, causing orbital abscess. 3. Intra-conal Compartment (located within the muscle cone): - Benign tumors: Such as lymphangioma, hemangioma, optic nerve glioma. - Malignant tumors: Including lymphoma, metastases, and neuroblastoma. - Inflammatory conditions like orbital pseudotumor or granulomatous diseases (e.g., sarcoidosis). - Vascular lesions like vascular malformations (e.g., arteriovenous malformations). 4. Extra-conal Compartment (around the muscle cone): - Lacrimal gland masses: Such as lacrimal gland tumors (benign or malignant). - Infections and inflammatory diseases affecting the orbital fat or the muscles.
Step 2: Imaging Features of Pathologies Affecting the Intra-conal Compartment of the Orbit.
The intra-conal compartment is bounded by the ocular muscles, the optic nerve, and the bone of the orbit. Lesions in this area can result in significant proptosis, especially when they compress the optic nerve or displace the ocular muscles. Imaging modalities like CT and MRI are invaluable for assessing the intra-conal compartment. (1) Orbital Hemangioma (Vascular Tumors): - MRI: These tumors are often well-circumscribed, hyperintense on T2-weighted images and hypointense on T1-weighted images. On contrast-enhanced MRI, these lesions show heterogeneous enhancement with areas of vascular flow voids. - CT: May show a well-defined mass that is hyperdense on non-contrast images with enhancement post-contrast. (2) Optic Nerve Glioma: - MRI: Optic nerve gliomas are typically isointense or slightly hypointense on T1-weighted images and hyperintense on T2-weighted images. The tumor may cause fusiform enlargement of the optic nerve. Contrast-enhanced MRI shows enhancement of the tumor along the optic nerve. - CT: May show optic nerve enlargement but is less sensitive compared to MRI. (3) Lymphangioma: - MRI: These lesions are usually multiloculated with cystic spaces and high signal intensity on T2-weighted images. The lesion often shows variable enhancement with contrast, and flow voids may be present within the cystic spaces due to vascular channels. - CT: Low attenuation on non-contrast images, with enhancement following contrast. It shows cystic structures. (4) Orbital Pseudotumor (Idiopathic Orbital Inflammation): - MRI: It presents as a diffuse mass involving the muscles and orbital fat. The lesion shows uniform enhancement with contrast and is hypointense on T1-weighted images and hyperintense on T2-weighted images. - CT: There is orbital soft tissue swelling with no distinct margins and orbital fat stranding. There may be muscle enlargement with irregular contours. (5) Metastatic Tumors: - MRI: Metastatic lesions in the intra-conal compartment are usually solid, with poorly defined borders and variable signal intensity. These tumors may show marked enhancement with contrast, and they can displace the muscles and the optic nerve. - CT: These lesions are hyperdense with contrast enhancement and may cause bony involvement or destruction in advanced stages. (6) Neuroblastoma: - MRI: Neuroblastoma in the intra-conal compartment presents as a solid mass, often hyperintense on T2-weighted images and hypointense on T1-weighted images, with extensive enhancement following contrast administration. - CT: Appears as a well-defined or irregular mass with enhancement, and it may show calcifications. (7) Lacrimal Gland Tumors (e.g., Adenoma, Adenocarcinom: - MRI: Lacrimal gland tumors in the intra-conal space show well-defined masses that are isointense or hyperintense on T2-weighted images and hypointense on T1. They exhibit homogeneous enhancement after contrast administration. - CT: These tumors can cause enlargement of the lacrimal gland with variable density on non-contrast images.