CASE 2846 Published on 30.01.2007

A multirow CT evaluation in a case of orbital decompression

Section

Head & neck imaging

Case Type

Clinical Cases

Authors

Cappelli C, Torri P, Pratali A, Vagli P, Mazzeo S.

Patient

43 years, female

Categories
No Area of Interest ; Imaging Technique CT, CT, CT, CT
Clinical History
A patient presented with Grave’s disease complicated by a severe ophthalmopathy.
Imaging Findings
A patient presented with Grave’s disease complicated by a severe ophthalmopathy. The clinical symptoms included photophobia, increased tearing associated with conjunctival hyperemia, palpebral oedema and diplopia. A clinical examination was done, which showed the presence of severe exophthalmus and a decreased visual acuity. The patient was previously treated by means of a high-dose corticosteroid therapy without clinical response. Therefore, orbital decompression was suggested and the patient was referred to our institute to undergo a spiral CT examination for surgical planning. The CT scan showed a severe proptosis (distance from the bizigomatic line 29–30 mm, Fig. 1a), an increased thickness of all extrinsic oculomotor muscles, especially the medial straight muscle (12 mm on the right side and 11 mm on the left side Fig. 1b) and the superior straight muscle (8 mm on the right side and 10 mm on the left side, Fig. 1c). The coronal images and MPR reformations revealed initial signs of compression of both the optic nerves due to reduction of the fatty cleavage between the medial straight muscles and the medial portion of the nerve (Fig. 2a, b). The patient underwent surgical intervention with a bilateral four-wall decompression (superior, lateral, medial and posterior orbitotomy) (Fig. 3a–c). A multirow CT evaluation performed after surgery revealed an important reduction in proptosis (distance from the bizigomatic line, 24 mm bilaterally) and the disappearance of nervous compression at the level of the orbital apex (Fig. 4a, b). However, both optic nerves showed a mild scoliotic appearance and both the medial muscles exhibited an increased thickness because of the retraction of the intraorbital structures after decompression (Fig. 4c).
Discussion
Grave's disease, which is the most common cause of hyperthyroidism worldwide, is an autoimmune disorder characterized by thyroid-stimulating hormone receptor antibody production. A shared antigenicity between the thyroid receptors and the orbital tissue is believed to be responsible for the ophthalmopathy, which is clinically observed in 50% of the patients. The ocular manifestations of Graves’ disease vary in severity from mild corneal exposure to vision loss and are a function of the degree of inflammatory infiltration. Sequelae include proptosis, lid retraction with subsequent exposure keratitis and restriction of extraocular movements resulting in diplopia. In some patients (5%), the optic nerve becomes compressed in the orbital apex, which results in impaired visual acuity and visual field defects. In the early inflammatory phase, an appropriate treatment includes systemic corticosteroids and external beam irradiation. The orbital manifestations during the stable phase are generally unresponsive to steroids and radiotherapy. Surgery is undertaken during this phase and includes strabismus repair, lid retraction surgery and orbital decompression (which allows to create additional space, into which enlarged orbital tissue can recede). An orbital decompression is indicated for patients with compressive optic neuropathy and/or corneal exposure, however, reduction of disfiguring proptosis for aesthetic reasons is increasing. The imaging evaluation includes the US, CT and MR examinations. The US allows the evaluation of the extrinsic oculomotor muscles, although only little information about the optical nerve at the orbital apex and the degree of proptosis can be obtained. CT and MR allow for a careful evaluation of the degree of proptosis and the extrinsic muscle thickness, and give information about the indirect signs of a compressive optic neuropathy. In particular, an MRI offers more possibilities for the tissue typing because it shows early degenerative phenomena of the extrinsic muscles and structural variations of the postorbital cellular flail tissue. However, a CT scan allows to assess the degree of ophthalmopathy without contrast administration, thereby avoiding the patient’s exposure to the effects of an iodine load. In particular, a multirow CT allows very fast and volumetric acquisitions, with thin slices (1 mm) and high space resolution, and guarantees a higher diagnostic performance compared to an axial conventional CT. Volumetric acquisition is suitable for many reformatting approaches such as multiplanar reconstructions (for visualization of the entire course and spatial relationships of the optical nerves) and volume rendering to obtain the three-dimensional representation of bony orbital walls in patients treated with surgical decompression. The evaluation of the bony breaches located in the posterior orbital surface (greater wing of the sphenoid bone), the lateral orbital surface (greater wing of the sphenoid bone and orbitalis processus of the zygomatic bone) and the superior orbital surface (processus orbitalis of the frontal bone) can be done on the three-dimensional images (volume rendering). A qualitative analysis relative to medial bone surface (papyraceous plate of the ethmoid) and inferior bone surface demolition can be obtained only by means of native axial or coronal images, while three-dimensional reformations cannot visualize the breaches of these bony walls for the presence of overlapping osseous structures.
Differential Diagnosis List
Severe Grave’s ophthalmopathy treated with surgical decompression.
Final Diagnosis
Severe Grave’s ophthalmopathy treated with surgical decompression.
Case information
URL: https://eurorad.org/case/2846
DOI: 10.1594/EURORAD/CASE.2846
ISSN: 1563-4086