Diagnostic Imaging in Patients with Orbital Cellulitis and Inflammatory Pseudotumor Fumiyuki Uehara, M.D. Norio Ohba, M.D. We have had the opportunity, at an eye clinic, to examine and treat a patient with orbital inflammatory disease of which the main symptom was severe eyelid swelling. When a patient has general symptoms of an infection, and a pathogenic organism is isolated and detected in an orbital lesion or blood culture, she or he is aggressively treated for orbital cellulitis with antibiotics and surgical drainage. 1 Staphylococcus and Streptococcus species are the most frequent pathogens in adulthood. With respect to the microbiological spectrum in childhood, it was recently reported that Streptococcus species are the predominant cause of orbital cellulitis now that Haemophilus influenzae bacteremia has decreased in the United States, owing to the advent of an H. influenzae bacteremia vaccine. 1 However, we sometimes encounter a patient who has eyelid swelling without general symptoms or bacteremia. In such a case, it is not easy to differentiate orbital cellulitis from inflammatory pseudotumor, which comprises nongranulomatous idiopathic inflammation within the orbit. 2 The treatment strategies are different for these inflammatory disorders: Orbital cellulitis is basically treated with antibiotics, whereas steroid therapy is effective for inflammatory pseudotumor. 2 Therefore, a differential diagnosis is important for the treatment of these orbital disorders. Recently, magnetic resonance imaging (MRI) has been widely used for the diagnosis of orbital inflammatory disorders. 2,3 The findings on MRI or computed tomography (CT) have usually been included in recent case reports of orbital cellulitis 4,5 and inflammatory pseudotumor. 2,6,7 However, little literature has described how to distinguish orbital cellulitis from inflammatory pseudotumor on the basis of MRI findings. In the present study, therefore, we retrospectively examined our cases at Kagoshima University Hospital to characterize the MRI features of orbital inflammatory diseases for the differential diagnosis between orbital cellu- 133
134 Uehara and Ohba litis and inflammatory pseudotumor, comparing our findings with those in previous reports. 2 9 Case Reports We have been using MRI for the examination of orbital disorders since 1995. With respect to orbital inflammatory disorders, we have identified 16 patients (8 men and 8 women) up to mid-2000 who were examined by means of MRI. The MRI patterns were classified into six types on the basis of imaging features, as described here. Preseptal Diffuse Type Patient 1, a 76-year-old woman, presented with swelling of the left eyelid. MRI showed isointense and hyperintense homogeneous signals representing edema of the eyelid and subcutaneous tissue anterior to the orbital septum in T 1 - and T 2 -weighted images, respectively (Fig 1A, B). In this patient, preseptal cellulitis was diagnosed, and thus the patient was treated with antibiotics. Similar MRI findings in the eyelid were observed in two other patients, a 20-year-old woman and a 64-year-old man, who had preseptal cellulitis induced by the spread of bacteria from the lacrimal sac with dacryocystitis. Orbital Diffuse Type Patient 2, a 64-year-old woman, experienced fever and symptoms of upper respiratory tract inflammation preceding her ocular symptoms of swelling and pain of the left eyelid, proptosis, diplopia, and disturbance of eye movement. A T 1 -weighted image showed that the infiltrative process of the intraconal and extraconal fat was isointense with respect to extraocular muscles (see Fig 1C). A T 2 -weighted image showed that the orbital lesion consisted of isointense and hyperintense signals (see Fig 1D). A T 1 -weighted image with fat suppression showed the lesion with hyperintense signals more clearly (see Fig 1E). The ethmoid sinus was observed to be filled with a hyperintense material in T 1 - and T 2 -weighted images (see Fig 1C E). The medial wall of the orbit appeared to have a gap in the middle region. The irritant was considered to have spread from the ethmoid sinus to the orbit. This patient was given a diagnosis of orbital cellulitis and thus was administered antibiotics. Although the orbital inflammation disappeared with the treatment, the ethmoid lesion remained almost unchanged (see Fig 1F). Then, this lesion was surgically removed by an otorhinolaryngologist. Orbital Reticular Type Patient 3, a 15-year-old boy, complained of right orbital pain and diplopia with chemosis of the right temporal conjunctiva, right ocular
MRI of Orbital Inflammatory Disease 135 Figure 1. Axial images of a 76-year-old woman with swelling of the left eyelid (A, B), and a 64-year-old woman with left eyelid swelling and proptosis (C E, before treatment; F, after treatment). (A, C, F: T 1 -weighted images; B, D: T 2 -weighted images; E: fat-suppressed T 2 -weighted image.) proptosis, and limited eye movement. At first, in this case differentiating between bacterial orbital cellulitis and inflammatory pseudotumor was difficult because abnormal findings on MRI were detected not only in the orbit but also in the ethmoid sinus, as in patient 2 (Fig 2). However, the MRI pattern of patient 3 was very different from that of patient 2. MRI showed eyelid edema, enlargement of the extraocular muscle, an intraconal reticular-pattern lesion, and thickened ethmoid sinus mucosa. The reticular pattern of the orbital fat, which appeared isointense as to extraocular muscles in both T 1 - and T 2 -weighted images (see Fig 2A, B), was considered to be a specific feature of inflammatory pseudotumor. 3 The absence of general symptoms was also suggestive of idiopathic orbital inflammation.
136 Uehara and Ohba Figure 2. Axial images of a 15-year-old boy with right conjunctival chemosis and proptosis. (A, B) Initial onset. (C, D) After steroid therapy. (E, F) Second recurrent stage. (A, C, E: T 1 -weighted images; B, D, F: T 2 -weighted images.) This patient was given steroids. The inflammatory lesion disappeared except in the posterior region of the ethmoid sinus mucosa (see Fig 2C, D). Unfortunately, the patient had a recurrence of the orbital inflammation in mid-2000. MRI again showed eyelid edema, enlargement of the extraocular muscle, an intraconal reticular-pattern lesion, and thickness of the posterior ethmoid sinus mucosa (see Fig 2E, F). After the inflammation had been treated with steroids, the ethmoid lesion was endoscopically resected by an otorhinolaryngologist. The histopathological features of the ethmoid sinus showed chronic inflammation with fibrosis. Myositis Type Patient 4, a 32-year-old man, complained of diplopia with chemosis of the temporal conjunctiva of the right eye, right ocular proptosis, and
MRI of Orbital Inflammatory Disease 137 limited eye movement. In this patient, the diagnosis was orbital myositis with preseptal inflammation and treatment was with steroids. MRI showed thickening of the lateral rectus muscle, of which the tendon was also enlarged. A hyperintense signal was heterogeneously detected in the isointense signal of the enlarged muscle and the edematous eyelid in both T 1 - and T 2 -weighted images (Fig 3A, B). The myositis pattern was detected using MRI in 2 other patients also, a 40-year-old woman and a 77-year-old man. Periscleritis Type Patient 5, a 14-year-old boy, complained of right ocular pain and diplopia with chemosis of the right conjunctiva, and disturbance of eye movement. MRI showed unilateral thickening of the right posterior periscleral region as an isointense signal relative to the extraocular Figure 3. Axial images of a 32-year-old man with right conjunctival chemosis (A, B), a 14-year-old boy with right conjunctival chemosis (C, D), and a 42-year-old man with left ocular pain (E, F). (A, C, E: T 1 -weighted images; B, D, F: T 2 -weighted images.)
138 Uehara and Ohba muscles in a T 1 -weighted image (see Fig 3C), and a hyperintense signal with respect to the orbital fat in a T 2 -weighted image (see Fig 3D). This boy was treated with steroids for periscleritis, which can be included in a localized form of inflammatory pseudotumor. Patient 6, a 42-year-old man, complained of left ocular pain and diplopia. MRI showed unilateral thickening of the left posterior periscleral region with almost the same signal intensities as those of patient 5 on T 1 - and T 2 -weighted images (see Fig 3E, F). This patient was also treated with steroids for periscleritis. Sclerosing Type Patient 7, a 46 year-old woman, complained of diplopia with chemosis of the right conjunctiva, displacement of the right eye to the temporal side, and limited ocular movement. MRI showed a mass lesion localized in the superonasal orbit. The mass lesion showed heterogeneous signal intensities hypointense to isointense signals and isointense to slightly hyperintense signals in T 1 - and T 2 -weighted images, respectively, relative to the extraocular muscles (Fig 4A, B). The presence of indentation of the globe suggested that this lesion was hard. The mass lesion was significantly reduced by steroid therapy (see Fig 4C, D) and was considered to be a sclerosing form of inflammatory pseudotumor. This pattern was detected also on MRI in 5 other patients: 84-, 61-, and 31-year-old women and 62- and 66-year-old men. Figure 4. Coronal images of a 46-year-old woman with right conjunctival chemosis and displacement of the right eye to the temporal side. (A, B) Before treatment. (C, D): After steroid therapy. (A, C: T 1 -weighted images; B, D: T 2 -weighted images.)
MRI of Orbital Inflammatory Disease 139 Discussion In the present study, we have described six types of MRI patterns of orbital inflammation. Two of these the preseptal diffuse (patient 1) and orbital diffuse forms (patient 2), reflect the MRI features of orbital cellulitis. Chandler and colleagues 10 have classified orbital cellulitis into five types: type I, inflammatory edema of the eyelid; type II, diffuse orbital cellulitis; type III, subperiosteal abscess; type IV, orbital abscess; and type V, cavernous sinus thrombosis. Patients 1 and 2 in this report correspond to Chandler types I and II, respectively; we do not currently have other patients whose-features correspond to types III, IV and V. The MRI features of orbital cellulitis adopted a relatively diffuse pattern in both the preseptal (Chandler type I) and orbital forms (Chandler type II). The signal intensities were also common to both types, there being isointense and hyperintense signals with respect to extraocular muscles in T 1 - and T 2 -weighted images, respectively. These MRI features are useful for the diagnosis of diffuse-type cellulitis. Previous reports have described CT and MRI findings of Chandler types III 8,9 and IV. The MRI features of an orbital abscess (Chandler type IV) have been reported to show a slightly hyperintense signal of a mass accompanied by a low-intensity signal of its capsule with respect to extraocular muscles on T 1 -weighted imaging, whereas the intensity of the mass has been shown to increase on T 2 -weighted imaging. 11 This MRI finding is almost the same as that of the ethmoid sinus revealed on MRI in patient 2 (see Fig 1C, D). It has been reported that when a mucopyocele is present, the infection causes increased viscosity, by which the lesion appears hyperintense in T 1 - and T 2 -weighted images. 12 Because the ethmoid sinus lesion in patient 2 displayed this MRI feature, the lesion is considered to be a mucopyocele, from which the organism may have spread into the orbit to induce orbital cellulitis. On the basis of these findings, a mucopyocele, an orbital abscess, and a subperiosteal abscess may appear similar on MRI. We observed that dacryocystitis, which induces preseptal cellulitis, also shows similar MRI findings. Dilatation of the superior opthalmic vein, which is enhanced with gadolinium-dtpa, has been reported to be accompanied by orbital cellulitis. 4 In this case, inflammation was considered to have spread from the parasinus to the orbit through this dilated and inflamed vein. 4 In a case that does not have a direct connection through the invaded orbital wall between the orbit and the sinus, this MRI feature may be important for the diagnosis of orbital cellulitis and determination of the primary inflamed lesion. Several malignant tumors, including extramedullary plasmacytomas, 13 malignant lymphomas, 14 and ethmoid sinus osteomas, 15 have been reported to present as orbital cellulitis. A case of neutrophilic eccrine hidradenitis resembling orbital cellulitis has been reported in a patient
140 Uehara and Ohba undergoing induction chemotherapy for acute myelogenous leukemia. 16 We have not seen such a case, but MRI is also useful for the diagnosis of these forms of secondary orbital cellulitis, although these disorders are not bacterial in a strict sense. Two cases of bacterial orbital cellulitis in patients with the acquired immunodeficiency syndrome have been reported. 5 In the case of general sepsis, although a lesion in the neighborhood may be absent, the presence of general symptoms may be helpful for the diagnosis. Two cases of orbital cellulitis induced by infective endocarditis have also been reported, 17 it being concluded that the presence of cranial MRI lesions is useful for the prompt early diagnosis and treatment of endocarditis. Using CT or MRI, orbital inflammatory pseudotumor has been classified into five types based on the distribution and localization of the lesion (lacrimal gland, localized type; myositis type; periscleritis or scleritis type; posterior orbita, localized type; and diffuse orbital type). 2,6 Patient 3 was considered to represent a diffuse orbital form of an inflammatory pseudotumor based on the MRI features, which included a reticular pattern. The reticular pattern of the orbital fat, which appears isointense in relation to extraocular muscles in both T 1 - and T 2 -weighted images (see Fig 2A, B), has been reported to be a specific feature of inflammatory pseudotumor. 3 This MRI feature is considered to be useful for the diagnosis of a diffuse orbital form of inflammatory pseudotumor. Nonspecific, polymorphous infiltration of inflammatory cells has been reported, with variable extents of fibrosis depending on chronicity. 3 The amount and thickness of the reticular orbital fat at initial onset (see Fig 2A, B) appears to be greater than that which occurs in the second recurrent stage (see Fig 2C, D). These differences may be attributable to the time lapse between the orbital inflammation and the MRI examination. When the inflammatory process is localized to the orbital muscles, MRI shows the myositis form (patient 4; see Fig 3A, B). MRI findings of this form of inflammatory pseudotumor have been mentioned in recent case reports of myositis: These findings include enlargement of the superior levator palpebrae muscle or extraocular muscles in orbital myositis. 7,18 In patient 4 in the present study, the tendon of the lateral rectus muscle was enlarged as well (see Fig 3A, B). This myositis form of inflammatory pseudotumor should be distinguished from dysthyroid orbitopathy, which is not accompanied by tendon thickening. This MRI feature of absence of a thickened tendon is considered to be specific to dysthyroid orbitopathy 2 and so facilitates the differentiation of dysthyroid orbitopathy from inflammatory pseudotumor. When the inflammation is localized to the periscleral or scleral region, MRI appears to be highly advantageous for discriminating periscleritis from scleritis. One previous report did not mention CT or MRI findings of either periscleritis or scleritis, 2 whereas another described CT scans of a patient with a thickened scleral region in whom scleritis was diagnosed. 6
MRI of Orbital Inflammatory Disease 141 We reported MRI of two patients with the periscleritis form (patients 5 and 6; see Fig 3C F). T 2 -weighted images demonstrated enlargement of the periscleral region, which could be clearly discriminated from the sclera as a hyperintense signal region (see Fig 3D, F), although it was combined with the sclera as an isointense signal region on T 1 -weighted imaging (see Fig 3C, E). Like the T 1 -weighted image, CT cannot be used to separate the sclera from the periscleral region. With respect to scleritis, a thickened sclera usually is demonstrated as a low-intensity signal region on T 2 -weighted imaging. Thus, for the differential diagnosis between periscleritis and scleritis, T 2 -weighted MRI is required. In both patients 5 and 6, MRI also showed that the lateral rectus muscle was affected by the inflammation, which was considered to be the cause of the ocular movement disturbance. Patient 7 is considered to have one of the localized forms of inflammatory pseudotumor, which is localized in the superonasal region of the orbit. This type of localization has not been included in the previous classification based on CT and MRI findings. 2,6 Therefore, we propose that an inflammatory pseudotumor that forms a mass lesion in the orbit should be included as a sclerosing form of inflammatory pseudotumor despite the names reflecting the localization regions. It is possible that the reticular form gradually changes to this form as the chronic inflammation continues. Nonetheless, the sclerosing form of inflammatory pseudotumor should be discriminated from other orbital tumors including lymphoproliferative disorders. Cases of benign reactive lymphoid hyperplasia and malignant lymphoma also show heterogeneous signal intensities, hypointensities to isointensities and isointensities to hyperintensities in T 1 - and T 2 -weighted images, respectively, in relation to the extraocular muscles. 3,19 Therefore, MRI does not exhibit tissue specificity for reliable differentiation among the sclerosing form of inflammatory pseudotumor, benign reactive lymphoid hyperplasia, and malignant lymphoma. Histopathological examination is required for a definitive diagnosis. Conclusions MRI is considered to be effective for the differential diagnosis of orbital cellulitis and inflammatory pseudotumor. The most diagnostic MRI feature of orbital cellulitis is diffuse patterns, the signals being isointense and hyperintense in T 1 - and T 2 -weighted images, respectively. On the other hand, the most diagnostic MRI feature of inflammatory pseudotumor is a reticular pattern with isointense signals in both T 1 - and T 2 -weighted images in the orbital fat. MRI is also effective for the detection of localized inflammatory pseudotumors, especially for the detection of periscleritis.
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