CT and MR Imaging in the Diagnosis of Scleritis

Discussion

Although clinically scleritis is classified according to an anterior or posterior location and subdivided into diffuse or nodular (focal) forms,^12,13 there has been no defined classification applied to imaging studies. Inflammation or infection of the sclera as observed on CT or MR imaging is generally referred to as “scleritis” independent of location or etiology. Anterior scleritis is the most common form, readily diagnosed on direct observation without the need for imaging.^2,12 Posterior scleritis accounts for 2%–12% of cases and is widely underdiagnosed because of its rarity, variable clinical findings, and unfamiliarity with this condition of the general ophthalmologist and radiologist.^2,6 The etiology of scleritis is most often inflammatory noninfectious, occurring either as an idiopathic condition (43%) or as a manifestation of a systemic disease (48%),^7,12,14 most often autoimmune. Rheumatoid arthritis and granulomatosis with polyangiitis are the most common underlying conditions. Idiopathic inflammatory scleritis might occur isolated or associated with extraocular anomalies and, we believe, as suggested by other authors,^{10,11,15⇓–17} is part of the IOID/pseudotumor spectrum. We identified a systemic disease in 2 patients (granulomatosis with polyangiitis, juvenile idiopathic arthritis). In addition, 2 patients had Down syndrome, which to our knowledge has not been specifically associated with scleritis; both patients presented with extensive IOID. Infectious scleritis is rare, particularly in the absence of predisposing factors.^3,4 In our series, 1 case was identified in an immunosuppressed patient.

The most distinctive clinical feature of scleritis is orbital pain, present in around 60% of patients.³ Orbital pain occurred in 7 of our 11 cases. From the remaining 4 cases, 3 presented with headaches. Decreased vision has been described to occur in up to 31% of patients, 3% developing permanent visual loss.¹ We found visual symptoms in 6 cases, 5 of which resolved completely with treatment. Fever is a feature in infectious scleritis. Treatment depends on etiology and, excluding infectious causes, involves nonsteroidal anti-inflammatory drugs, corticosteroids, and immunosuppressive drugs.^3,18

Correctly diagnosing scleritis is important given the potential for complications and the frequent association with systemic disease, of which scleritis might be the presenting manifestation.^2,3,14 Because the posterior sclera cannot be directly visualized, imaging methods are needed to make or confirm the diagnosis in clinically challenging cases. Sonography is the most widely used imaging technique, but often fails to show pathognomonic findings and is of limited value in evaluating other intraorbital structures.^2,19 Scleritis is frequently part of a more extensive inflammatory process, which might involve other orbital structures. In our series, sonography was performed by a specialized ophthalmologist in 4 patients and was diagnostic in 1 patient. Sonography was not performed in the remaining patients because scleritis was not clinically suspected.

MR imaging has excellent soft tissue contrast and the ability to image the entire orbit. On T2-weighted sequences, the posterior globe wall appears as a single hypointense ring, whereas on T1-weighted sequences, the sclera can be individualized as the outer hypointense rim of the globe. A distinct hyperintense and enhancing rim can be seen internal to the sclera, corresponding to the choroid, and, at least partially, to the retina (Fig 2B).

Direct signs of scleritis on imaging are scleral enhancement, scleral thickening, and focal periscleral cellulitis. Our most consistent finding was scleral enhancement, present in 100% of contrast-enhanced examinations. Enhancement might involve the whole sclera (Fig 1B) or be preferentially peripheral (Fig 2), perhaps illustrating different degrees of inflammation, starting from the vascularized outer aspect of the sclera. It also might extend along the optic nerve sheath (Fig 5), representing optic perineuritis. Scleral enhancement is always abnormal and should not be confused with choroidal enhancement, a physiologic finding. Use of contrast is critical because scleral enhancement might be the only positive finding (Fig 2).⁵ On MR imaging, postcontrast T1WI should be acquired with fat saturation because the fat signal might mask scleral enhancement. Another sign of scleritis is scleral thickening, present in 83% of our patients and easily identified on MR imaging. On CT, though the globe layers cannot be separated, we found eccentric globe wall thickening and peripheral enhancement in all patients, making CT a useful tool in the diagnosis of scleritis.^6,11,20 Periscleral cellulitis, described as the “ring sign” by Chaques et al,¹¹ is also an important sign of scleritis, found in 42% of our patients. Imaging findings are summarized in Table 2.

Indirect signs of scleritis include retinal and choroidal detachment and effusion in the suprachoroidal or Tenon spaces.⁶ There might be associated uveitis,^18,21 which can be differentiated from scleritis, particularly on MR imaging.

Scleritis also might be associated with extraocular orbital abnormalities, as seen in 5 of our cases, such as pre- and postseptal cellulitis, myositis, or dacryoadenitis. When scleritis occurs with anterior cellulitis, the clinical picture is often mistaken for infectious orbital cellulitis. Because extension of an orbital infection to the sclera is extremely rare in immunocompetent patients, coexistence of cellulitis and scleritis on imaging should raise suspicion of an inflammatory noninfectious etiology.³ Other clues pointing to an inflammatory etiology include subacute/chronic complaints and absence of fever, infectious parameters, or sinusitis.

The differential diagnosis of scleritis on imaging mainly is tumor, particularly with nodular scleritis, with published cases of globe tumors misdiagnosed as scleritis¹⁴ and scleritis mimicking a choroidal mass.^8,9 In the diffuse form of scleritis, posterior uveitis, diffuse melanoma, and lymphoma are the most relevant differential diagnoses. CT and MR imaging have proved useful in distinguishing these entities.²⁰ In challenging cases, a therapeutic trial (with nonsteroidal anti-inflammatory drugs or steroids)¹⁵ and/or histopathologic confirmation might be warranted because misdiagnoses of scleritis have been described to lead to inadvertent enucleations.⁹ In the presented case with melanoma as the presumptive diagnosis (patient 4), imaging and treatment with corticosteroids led to resolution of the mass, making a biopsy unnecessary. Clues to the inflammatory (versus neoplastic) nature of the process include the presence of pain, cellulitis as seen on imaging, and the specific scleral location, though some intraocular tumors might also involve the sclera. Additional MR sequences, such as DWI, might be of benefit,²² particularly in lymphoma, which often demonstrates restricted diffusion.²³ Neither DWI nor other advanced imaging sequences were routinely performed in our patients.

Although we present a small group of patients, they illustrate a wide range of direct and indirect imaging findings in scleritis. CT and MR imaging provided useful information and influenced clinical decision-making. MR imaging is the most useful examination in the diagnosis of scleritis,^5,9 differentiating the sclera from the other ocular layers. In our experience and as ascertained by previous studies,^6,11,20 CT is also able to diagnose scleritis, showing eccentric outward globe wall thickening and enhancement, frequently associated with periscleral cellulitis. Both techniques are more informative than ultrasonography for assessment of extraocular extension of disease.

We suggest that in cases when clinical evaluation and ultrasonography do not suffice in the diagnosis of scleritis, or when associated ailments are suspected, MR imaging be performed. When MR imaging is not available, or when there are contraindications, CT can be of diagnostic value.

The results of our study are limited by its retrospective nature, the small number of patients, and the lack of a standardized protocol. Despite this, we believe that this article contributes to the current knowledge on imaging signs of scleritis on CT and MR imaging. To the best of our knowledge, this is the largest series of MR imaging in scleritis analyzed to date.