Ординатура / Офтальмология / Английские материалы / Clinical Ophthalmic Echography_Harrie_2008

bilateral proptosis in adults. Imaging is useful to confirm the diagnosis and to monitor disease activity in some cases. MRI with fat suppression or STIR sequence can demonstrate extraocular muscle inflammation that confirms that the disease is in an active inflammatory stage that should respond to immunosuppression. The spent disease will not respond to immunomodulation and as such this distinction is clinically useful. Features of thyroid eye disease include enlarged extraocular muscles with sparing of the myotendinous insertions (Fig. 370), lacrimal gland enlargement,

proptosis, and apical crowding. There may be dirty fat and increased orbital fat volume. There may be an association with sinus disease. In dysthyroid optic neuropathy, either the orbital apex is crowded to the extent that the optic nerve becomes compressed and an optic neuropathy ensues or the optic nerve may also lose its sigmoid shape and appear straight and the assumption is made that it is stretched by progressive proptosis with presumed microvascular sequelae (Figs. 371–373). If this were the suspected diagnosis, then CT would be a more appropriate investigation because bony

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FIG. 370. Coronal computed tomography scan showing enlarged extraocular muscles (type 2 Graves’ disease)

decompression is a likely clinical outcome and CT is essential for surgical planning. Scans in patients with previous orbital decompression will show a mixture of findings depending on the nature of the

Part VIII. Orbital Imaging

FIG. 372. Coronal computed tomography scan showing enlarged muscles filling the orbital apex in a patient with dysthyroid optic neuropathy (arrows)

prior surgery. Prolapse of orbital contents into the paranasal sinuses is the desired result.

Idiopathic orbital inflammation (IOI) is a common disease of the orbit that has previously been

Part VIII. Orbital Imaging

described as orbital pseudotumor. It is usually but not always unilateral and may affect the lacrimal gland, the extraocular muscles, or the intraor extraconal space. The diagnosis is one of exclusion, with lymphoma being an important differential, although lymphoma is not normally painful. In contradistinction to thyroid eye disease, IOI is said to affect the extraocular muscle tendons. Posterior scleritis can be detected by thickening of the sclera, but ultrasound is the preferred investigation to allow measurements of the scleral thickness to be made.

Sarcoidosis

Sarcoidosis is rare in the orbit but may affect the lacrimal gland, the muscles, or the optic nerve. Radiologic features are nonspecific but imaging will assist with surgical planning for biopsy.

Infection

Orbital cellulitis may be preor postseptal and as such can threaten to communicate infection with the cavernous sinus via the superior ophthalmic vein (SOV), which can be a devastating consequence. The most common scenario, however, is a subperiosteal abscess associated with contiguous sinus disease. Imaging is aimed at establishing that there is not some other pathology, such as rhabdomyosarcoma, and for possible surgical intervention as via an orbitotomy. The disease often presents in the younger age group and, as a result, sedation may be required to obtain images. Coordination between the pediatrician, radiologist, and anesthesiologist is crucial.

Mucormycosis is a disease of the immunocompromised and more frequently affects diabetics. The failure to manage this condition appropriately can be fatal. Imaging is aimed at assessing the orbit, paranasal sinuses, and cavernous sinuses, and disease extent.

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ated (Fig. 374). The purpose of the investigation is to establish the extent of the bony defect and the degree of soft tissue entrapment. The pediatric population can mislead the clinician with the white-eyed blowout, where a trapdoor greenstick-type fracture can entrap the inferior rectus and lead to rapid muscle necrosis; urgent imaging and intervention is required. A feature that should alert the referring clinician and radiologist is if the child is systemically unwell, with constitutional symptoms including fever and severe nausea associated with muscle necrosis.

Both bone and soft tissue windows should be obtained with either direct or reformatted coronal views. The corresponding sinuses are usually opaque due to blood that may manifest as a fluid level seen on axial scans. Air inside the orbit is a telltale sign of communication between the orbits and the sinuses and surgical emphysema may also be seen. The CT equivalent of the teardrop sign seen on plain films should alert the clinician to a small fracture.

Orbital foreign bodies should be sought and excluded as far as is possible (Fig. 375). A more devastating consequence of trauma is optic nerve canal damage and or traumatic optic neuropathy. Traumatic optic neuropathy may be associated with fracture of the optic canal that can be seen on CT or may be a localized pressure effect with vascular consequences that are best seen on high-resolution MRI.

Trauma

The CT scan is the investigation of choice in most cases of trauma, particularly if there is even a vague suspicion of an orbital or intraocular foreign body.81 Fracture of the orbital rim is less common but the floor and medial wall are susceptible to blowout fracture with the zygomatic complex often associ-

FIG. 374. Computed tomography scan of orbital fracture (arrows)

FIG. 375. Computed tomography scan of orbital foreign body (arrow)

Caroticocavernous Fistulas

Caroticocavernous fistulas may be evaluated with an MRI, although selective carotid angiograms remain the gold standard but are not without risk. CT, MRI, and orbital ultrasound will show an enlarged SOV and proptosis. Orbital color Doppler can demonstrate aterialization of the SOV. The fistulae are categorized by the anatomy of the feeder vessels and the flow rate. A history of trauma (not necessarily), a bruit and blood in Schlemm’s canal, and an elevated intraocular pressure with conjunctival arterialization should prompt the diagnosis, which can be confirmed and characterized by imaging studies.

Pediatric Disease

The most common reason for obtaining a CT scan in children is in the context of orbital infection that is addressed above. It is worth noting that children can present with orbital cellulitis and a white eye and that other conditions can mimic orbital cellulitis.

The most common benign tumor in children is the capillary hemangioma. The most common orbital malignant tumor in children is a rhabdomyosarcoma, which has a variety of presentations that can mislead the clinician. A painless proptosis or a cellulitic picture can be the first sign of disease.

Summary

When presented with orbital disease, the clinician can aid diagnosis and plan appropriate surgical intervention with the judicious use of orbital imag- ing—CT, MRI, and ultrasonography. In general terms, CT is best for bony disease, for example, fractures, and for planning decompression. MRI is more useful for soft tissue interpretation. Ultrasound is an extremely useful adjunct. The location of the tumor and the imaging and associated features are helpful in reaching a differential diagnosis and in determining the likelihood of benign versus malignant disease.82