COMPUTED TOMOGRAPHY AND MAGNETIC RESONANCE IMAGING OF PEDIATRIC ORBITAL LESIONS

Abstract

Computed tomography (CT) is the first-line imaging modality for orbital evaluation especially in the acute setting. CT offers rapid image acquisition, high spatial resolution and suitable for the evaluation of fractures, calcifications, and radiopaque foreign bodies.

MR imaging offers exquisite contrast resolution of the orbital structures without exposing the patient to ionizing radiation. However, the presence of an orbital metallic foreign body is a contraindication to MR imaging. Also, sedation of children may be needed.

Traumatized patients are usually evaluated with CT. Evaluate the bony orbit for fractures, the anteriorchamber, position of the lens, the posterior segment of the globe for bleeds or abnormal fluid collections. Also, evaluate for foreign bodies and remember that wooden foreign bodies can mimic air on CT scans.

Retinoblastoma, the most common intraocular tumor of childhood, is distinguished from non-neoplastic lesions by the finding of dystrophic calcification. The association of bilateral retinoblastoma with a midline intracranial neoplasm is called “trilateral retinoblastoma”. So combined diagnostic CT and MRI is very important.

Medulloepithelioma is rare but if it involves the retina, it will show calcifications and differentiation from retinoblastoma is impossible without histologic examination.

Rhabdomyosarcoma is the most common extraocular orbital malignancy and demonstrates aggressive, infiltrative growth, frequently involving adjacent bone. This tumor grows rapidly and may invade the intracranial contents and metastasize to bone or lung.

PHPV is classically seen as a retrolental mass representing the persistent primary vitreous with a linear projection between the mass and the optic disc. There is no calcification and the globe is small.

Optic nerve glioma involves the optic pathways, causing fusiform enlargement at imaging. Bilateral lesions are virtually pathognomonic for NF1.

Hemangioma is a tumor of infancy and by age it gradually replaced by fibrofatty tissue. Because functional vision is necessary in early infancy to create neuronal visual pathways, orbital hemangiomas often require treatment to preserve vision. MRI is the modality of choice for its imaging due to its sensitivity in detecting vessels and blood products.

Venous-lymphatic malformation is unencapsulated and traverses tissue planes. This lesion is often distinguished by fluid-fluid levels appearance due to intralesional hemorrhage; its venous components may contain phleboliths. Unlike hemangioma, venous-lymphatic malformation grows with the patient age and never involutes.

Orbital infections represent more than half of primary orbital disease processes. The location of an orbital infection is described with respect tothe orbital septum, as either preseptal (periorbital)