Diagnostic imaging of the orbit and eye

Orbital imaging modalities

The choice of method depends on the clinical objective:

• Computed Tomography (CT): The primary and fastest imaging method. Ideal for bone evaluation, fracture detection, and foreign bodies. Contrast-enhanced CT is the first-line choice for infections and tumors. Axial slices are obtained parallel to the orbital axis so that the optic nerve and extraocular muscles fall within a single slice.
• Magnetic Resonance Imaging (MRI): Provides superior soft-tissue contrast resolution. It is the modality of choice for evaluating the optic nerve (e.g., in optic neuropathy). The standard protocol includes T1, contrast-enhanced T1, and T2 fat-suppressed sequences. Whole-brain scanning is mandatory to rule out concomitant lesions.
• Ultrasound (US): Useful for evaluating the eyeball itself (retina, anterior chamber) and for color Doppler flow mapping, but limited beyond the globe.
• Radiography: A historical method, currently used primarily for screening metallic foreign bodies prior to MRI.

Orbital Trauma and Foreign Bodies

Blunt trauma frequently results in fractures of the medial and inferior orbital walls. A trap-door fracture (trap-door fracture) can lead to herniation of orbital fat and the inferior rectus muscle (inferior rectus) into the maxillary sinus, where blood often accumulates (hemosinus). This results in enophthalmos (enophthalmos) and downward displacement of the globe (hypoglobus).

In penetrating injuries, CT helps differentiate the composition of foreign bodies:

• Metal: Appears as a markedly radiodense (radiodense) lesion, frequently accompanied by air bubbles within the vitreous body.
• Wood: A wooden splinter (wooden splinter) is visualized as a linear hypodense area resembling air. It is frequently accompanied by air accumulation in the anterior chamber of the eye.

Intraocular and Orbital Tumors

Retinoblastoma is a malignant intraocular tumor. The primary clinical sign is leukocoria (leukocoria), or the absence of a red reflex. Less commonly, it mimics orbital cellulitis. On CT, it presents as a hyperattenuating retrobulbar mass with calcification (95% of cases). MRI is used to assess intracranial extension.

Coats disease is a congenital vascular malformation that also manifests with leukocoria. Leakage of lipoproteinaceous exudate leads to retinal detachment. CT shows increased subretinal fluid density, while MRI demonstrates high T1 and T2 signal without contrast enhancement.

The orbit may also be affected by metastases (e.g., prostate carcinoma with bone sclerosis and exophthalmos) or local invasion by paranasal sinus cancer.

Ophthalmoplegia and Horner Syndrome

In ophthalmoplegia, it is crucial to trace the cranial nerve pathways: from the brainstem, through the cisterns, skull base foramina, and cavernous sinus, up to the superior orbital fissure.

Sympathetic innervation of the eye (disruption of which causes Horner syndrome) consists of a three-neuron chain:

1. First-order neuron: From the hypothalamus to the cervicothoracic junction. Brain and cervical spine MRI are indicated for diagnosis.
2. Second-order neuron: Extends to the superior cervical ganglion.
3. Third-order neuron: Follows the internal carotid artery into the orbit.

To evaluate the second- and third-order neurons, CT angiography from the aortic arch to the vertex (vertex) is recommended.

Class and exam questions

What else to study on this topic

• Detailed analysis of the causes of Horner syndrome by the site of neuronal lesion
• Differential diagnosis of leukocoria causes (retinoblastoma vs. Coats disease)
• MR spectroscopy in hypoxic-ischemic brain injury in pediatric patients
• Rhabdomyosarcoma as an extraocular neoplasm in children
• The role of SWI MRI sequences in detecting retinal hemorrhages

Other topics in the Neuroimaging section

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