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Extraconal orbital lesions are those located outside the muscle cone formed by the four rectus muscles and intermuscular septa. They typically cause eccentric (non-axial) proptosis, displacing the globe away from the lesion, in contrast to intraconal lesions (which cause axial proptosis).
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Important for differentiating lacrimal gland lesions, muscular pathology, and bony-origin tumors.
| Type | Etiology |
|---|---|
| Developmental / Cystic | • Dermoid/epidermoid cyst (most common pediatric orbital lesion; classically superolateral). |
| • Mucocele (from paranasal sinuses, esp. ethmoid/frontal). | |
| • Encephalocele/meningocele. | |
| Vascular | • Capillary hemangioma (infantile hemangioma). |
| • Lymphangioma. | |
| • Orbital varices (may extend from extraconal into intraconal). | |
| Neoplastic | Lacrimal gland tumors: |
| • Benign: Pleomorphic adenoma. | |
| • Malignant: Adenoid cystic carcinoma (most common), lymphoma, carcinoma ex pleomorphic adenoma. |
• Rhabdomyosarcoma (commonest primary malignant orbital tumor in children). • Metastasis (neuroblastoma in children; breast, lung in adults). • Osteogenic / fibrous lesions (osteoma, fibrous dysplasia). | | Inflammatory | • Idiopathic orbital inflammatory syndrome (orbital pseudotumor). • Thyroid-associated orbitopathy (TAO; commonest cause of adult proptosis). • Infectious: Orbital cellulitis, subperiosteal abscess. | | Traumatic / Miscellaneous | • Hematoma (post-traumatic). • Foreign body granuloma. |
General sign: Extraconal lesions → eccentric displacement of the globe, alteration of orbital fat planes.
| Condition | Imaging features |
|---|---|
| Dermoid cyst | • Well-circumscribed, usually superotemporal. |
| • CT: Hypodense, fat-fluid levels, may show calcification. | |
| • MRI: Hyperintense on T1 (fat content). | |
| Mucocele | • Expansile cystic lesion from sinus. |
| • Causes smooth scalloping, thinning of bony wall. | |
| • MRI: T1/T2 signal variable depending on protein content. | |
| Lacrimal gland tumors | • Pleomorphic adenoma: Well-defined, lobulated, superolateral mass. |
| • Adenoid cystic carcinoma: Poorly marginated, irregular, with bony destruction and perineural spread. | |
| Rhabdomyosarcoma | • Rapidly growing extraconal mass in child. |
| • Iso- to hypointense on T1, hyperintense on T2, intense enhancement. | |
| ‣ | • Bilateral extraocular muscle belly enlargement (spares tendinous insertions = “coke-bottle sign”). |
| • Inferior rectus most commonly involved. | |
| Orbital cellulitis / abscess | • CT: Orbital fat stranding, subperiosteal collection. |
| • Sinus involvement often seen (ethmoid). |
Cavernous hemangioma. Axial T2-weighted (A) and fat-saturated T1-weighted imaging with injection: immediate (B) and delayed (C).
Dreyfus Heran, F. (2017). Imaging an Orbital Mass: The Essential. Journal of the Belgian Society of Radiology, 101(S1), 2.
Lachrymal gland lymphoma T2-weighted (A), Post-contrast fat saturated T1-weighted (B), ADC (C), CDFI (D).
Dreyfus Heran, F. (2017). Imaging an Orbital Mass: The Essential. Journal of the Belgian Society of Radiology, 101(S1), 2.