A 55-year-old woman was presented to our Emergency Department (ED) with bilateral orbital apex syndrome (OAS). She had a 3-month history of headache, photophobia, subtle left ptosis, and bilateral forehead numbness, which prompted repeat ED visits. Cranial and orbital imaging on previous presentations was reported as normal. She had sensory complaints with a confirmed, mild sensory mononeuritis multiplex, and elevated myeloperoxidase autoantibodies at >8.0 U (normal < 1.0), raising suspicion of an ANCA-associated vasculitis. Over 1 month, her vision deteriorated with worsening retro-orbital pressure and pain with eye movements. Examination revealed visual acuity of 20/200 on the right and finger-counting on the left, left afferent pupillary defect, and bilateral inferior altitudinal hemianopia. Funduscopy showed raised left optic nerve with blurred nasal optic disc margins. There was severe bilateral ophthalmoplegia, bilateral periorbital swelling, left ptosis, and right V1 hypoesthesia. Remaining neurological examination was unremarkable. CT imaging revealed a soft tissue abnormality in the superior aspect of the left orbit, which was confirmed on MRI as an enhancing extraconal soft tissue mass (Figures 1 and 2). Enhancing infiltrates was also present in both orbital apices, yet more subtle on the right (Figure 2). Left orbital biopsy confirmed granulomatosis with polyangiitis (GPA). Treatment was initiated with IV steroids, followed by IV cyclophosphamide and ongoing oral prednisone. At follow-up, visual acuity and ductions returned to normal.

Figure 1: Abnormal soft tissue is demonstrated on CT post-contrast (red arrow) involving the left superior orbit.

Figure 2: MRI orbital imaging sequences showing T1 pre-contrast (A), T1 post-contrast (B), T2 fat-sat pre-contrast (C), T1 fat-sat pre-contrast (D) and T1 fat-sat post-contrast (E). Soft tissue mass involving the left superior extraconal fat tissue and superior rectus muscle (red arrows).The axial MRI MPR images show enhancing soft tissue extending from the orbital apices into the bilateral cavernous sinus (white arrows) with resultant apical crowding.

Orbital masses are a rare manifestation of GPA and associated with a refractory course and significant morbidity. ^{Reference Holle, Voigt and Both1} GPA, formerly Wegener’s granulomatosis, is a rare autoimmune disorder characterized by granulomatous inflammation and necrotizing vasculitis of small- and medium-sized blood vessels. 50%–60% of GPA patients have ophthalmic involvement, with up to 16% presenting initially with ocular findings. ^{Reference Pakrou, Selva and Leibovitch2} Of ocular presentations, orbital involvement is most frequent at 22%–45%. ^{Reference Murai, Kurimoto and Mori3} Orbital manifestations may be secondary to primary granulomatous vasculitis or contiguous sinus involvement. ^{Reference Pakrou, Selva and Leibovitch2} The latter mechanism is more common; infiltration from paranasal sinuses is demonstrated in 72% of orbital GPA cases. ^{Reference Holle, Voigt and Both1}

OAS comprises dysfunction of cranial nerves II, III, IV, VI and the ophthalmic branch of V and is reported in only a handful of cases of GPA. In most of these cases, OAS was caused by contiguous sinus or pachymeningeal infiltration. ^{Reference Murai, Kurimoto and Mori3–Reference Hisahara, Yamada and Matsuura8} OAS without contiguous sinus spread has been reported, but occurred in a patient with a pre-existing confirmed diagnosis of GPA. ^{Reference Shunmugam, Morley, Graham, D’Cruz, O’Sullivan and Malhotra9}

This case highlights several key points. First, despite profound ophthalmoplegia and severely compromised visual acuity, imaging findings were relatively subtle. In fact, to our knowledge, there has been only one previously reported case of ANCA-associated vasculitis causing OAS without corresponding radiographic abnormalities detected on MRI. ^{Reference Iwanami, Katoh, Ohnaka, Nakajima and Kawamura10} Second, despite a suspicion of systemic vasculitis given a mild sensory mononeuritis multiplex, an orbital biopsy was required to establish a definite histopathologic diagnosis. Finally, although the optic neuropathy and oculomotor dysfunction were severe at presentation, recovery to normal acuity and ductions demonstrates the robust long-term response to immunosuppression in this condition. In sum, close attention to the orbits is warranted when considering a diagnosis of ANCA-associated vasculitis. Imaging findings can be subtle, and diagnosis may be missed. ^{Reference Cooley, Pless and Stone7}