A Unique Radiologic Case of Optic Nerve Infarction in a Patient With Mucormycosis

This is a rare presentation of a unilateral optic nerve infarction of the left eye caused by mucormycosis in a 51-year-old man with poorly controlled Type 2 diabetes. Diffusion-weighted MRI of the orbit demonstrated extensive infarction of the left optic nerve with ipsilateral cavernous sinus thrombosis and periorbital adnexal inflammation. Left orbital exenteration and sinus debridement were performed, and mucormycosis involving the optic nerve sheath was confirmed on histopathology.

Photo and Video Essay Section Editors: Melissa W. Ko, MD Dean M. Cestari, MD Peter Quiros, MD A Unique Radiologic Case of Optic Nerve Infarction in a Patient With Mucormycosis Alexandria L. Chaulk, MD, Thai H. Do, MD, Emilio P. Supsupin, MD, Meenakshi B. Bhattacharjee, MD, Karina Richani, MD, Ore-Ofe O. Adesina, MD FIG. 1. A. Postcontrast T1 axial MRI showing proptosis of the left orbital globe with marked asymmetric thickening of the periorbital soft tissues, particularly on the nasal side (long arrow). There is also asymmetric conspicuity of enhancement in the intraconal space (short arrows) and abnormal hypoenhancement of the left medial rectus muscle (asterisks). Compare this to the normal avid enhancement of other extraocular muscles (arrowheads). B. T2 coronal MRI depicting abnormal signal in the orbital compartment. There is loss of definition of the optic nerve sheath (arrowhead). Compare this with the normal appearance of the right optic nerve sheath (double arrowheads). Abnormal signal elevation in the left inferior frontal lobe (arrow) is evident, reflecting cerebritis. Abstract: This is a rare presentation of a unilateral optic nerve infarction of the left eye caused by mucormycosis in a 51-year-old man with poorly controlled Type 2 diabetes. Diffusion-weighted MRI of the orbit demonstrated extensive infarction of the left optic nerve with ipsilateral cavernous sinus thrombosis and periorbital adnexal inflammation. Left orbital exenteration and sinus debridement were performed, and mucormycosis involving the optic nerve sheath was confirmed on histopathology. Journal of Neuro-Ophthalmology 2021;41:e354–356 doi: 10.1097/WNO.0000000000001179 © 2020 by North American Neuro-Ophthalmology Society Ruiz Department of Ophthalmology and Visual Science (ALC, THD, KR, O-OA), McGovern Medical School at The University of Texas Health Science Center at Houston (UTHealth), Houston, Texas; Robert Cizik Eye Clinic (ALC, THD, KR, O-OA), Houston, Texas; Department of Diagnostic and Interventional Imaging (EPS), McGovern Medical School at UTHealth, Houston, Texas; and Departments of Pathology (MBB) and Neurology (O-OA), McGovern Medical School at UTHealth, Houston, Texas. The authors report no conflicts of interest. Address correspondence to Ore-Ofe O. Adesina, MD, Robert Cizik Eye Clinic, 6400 Fannin Street, Suite 1800, Houston, TX 77030; E-mail: [e-mail] e354 A 51-year-old man with a history of poorly controlled Type 2 diabetes mellitus presented with 3 days of periorbital swelling and painless vision loss of the left eye after a fall. On initial examination, the left eye had visual acuity of no light perception with a relative afferent pupillary defect and complete ophthalmoplegia. The external exam of the left eye revealed periorbital edema, proptosis, and a black eschar in the medial aspect of the left upper eyelid. Mild conjunctival hyperemia and superficial punctate keratopathy were also noted on the anterior segment of the left eye. The ophthalmoscopic exam was unremarkable except for incidental findings of moderate nonproliferative diabetic retinopathy. MRI of the orbits revealed abnormal enhancement of the left preseptal and postseptal soft tissues, extending to the left orbital apex (Fig. 1). The left optic nerve seemed to be normal on T1, T2, and fluid-attenuated inversion recovery (FLAIR) sequences but demonstrated abnormal hyperintensity on diffusion-weighted imaging (DWI) with corresponding hypointensity on apparent diffusion coefficient (ADC) map (Fig. 2). The MRI findings in the left optic nerve are consistent with optic nerve infarction (1). Absence of Chaulk et al: J Neuro-Ophthalmol 2021; 41: e354-e356 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo and Video Essay FIG. 2. Axial diffusion-weighted imaging (A) demonstrating abnormal hyperintense signal of the left optic nerve (arrows) corresponding to a very hypointense signal (arrows) on apparent diffusion coefficient map (B), most consistent with diffusion restriction. Compare this with the typical low signal intensity of the normal contralateral right optic nerve on diffusionweighted imaging and apparent diffusion coefficient maps (arrowheads in A and B). enhancement in the adjacent ethmoid air cells and maxillary sinus cavity reflected devitalization of the sinonasal mucosa. There was also asymmetric enhancement and mild irregularity of the left cavernous sinus, concerning for ipsilateral cavernous sinus thrombosis. The patient underwent left orbital exenteration and sinus debridement. The histopathology of the surgical samples, including the optic nerve sheath, revealed tissue necrosis and invasive fungal infection with broad nonseptate hyphae branching at 90°, consistent with mucormycosis (Fig. 3). This was confirmed with fungal culture growing Rhizopus organisms. Despite surgical debridement and aggressive medical treatment, including intravenous amphotericin B, the patient developed left frontal lobe infarction from suspected infectious emboli. He declined further intervention and was subsequently transitioned to hospice care. Mucormycosis is a rare, opportunistic fungal infection in immunocompromised patients. The infection is characterized by extensive thrombosing vasculitis and tissue necrosis (2). Rhino-orbito-cerebral mucormycosis (ROCM) is the most common subclass, accounting for up to half of all cases. It is defined as orbital, nasal, and paranasal sinus infection with potential cerebral spread and can have a high mortality rate (2,3). Signs of ROCM include periorbital inflammation, orbital proptosis, ophthalmoplegia, acute vision loss, nasal eschar, and sinusitis (2). Optic nerve infarction caused by ROCM on neuroimaging is rare. To the best of our knowledge, there are only 4 reported cases in the literature (1,4–6). Ours is the first case to demonstrate concomitant radiographic and histopathologic evidence of optic nerve infarction secondary to mucormycosis invasion of the optic nerve (PubMed search using terms orbital mucormycosis, optic nerve infarction, and optic nerve ischemia on September 22, 2020). In our case, the left optic nerve ischemia was highlighted by the DWI sequence, although it appeared normal on T1, T2, and FLAIR sequences (Figs. 1, 2). These findings are consistent with those reported in the literature (1,4–6). Other causes of hyperintensity of the retrobulbar optic nerve on DWI with correlating hypointensity on ADC (restricted diffusion) include optic neuritis and other acute ischemic lesions in the optic nerve such as posterior ischemic neuropathy (7–9). Hyperintensity of the optic nerve on DWI with reduced ADC was described in the posterior segment of the optic nerve in cases of traumatic optic neuropathy (10). DWI signal with reduced ADC signal localized at the optic nerve head has been described in nonarteritic anterior ischemic optic neuropathy and in papilledema (11,12). Restricted diffusion has also been reported in a case of a primary atypical optic nerve sheath meningioma in a child (13). Our patient’s history and ophthalmologic exam were most consistent with a diagnosis of optic nerve infarction, FIG. 3. A. Hematoxylin and eosin stain of the left optic nerve, demonstrating pallor and loss of nuclei, consistent with infarction. B. Periodic acid–Schiff stain of the left optic nerve sheath with fungal hyphae and morphology consistent with mucormycosis. Chaulk et al: J Neuro-Ophthalmol 2021; 41: e354-e356 e355 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo and Video Essay which was confirmed with pallor and loss of nuclei of the optic nerve confirming infarction on histopathology (Fig. 3A). Optic nerve infarction may be a result of direct fungal invasion with subsequent thrombosis of the central retinal artery, ophthalmic artery, or optic nerve (2–4). In this case, fungal invasion of the optic nerve sheath was confirmed on tissue pathology (Fig. 3B). We present a rare, radiologic demonstration of optic nerve infarction caused by ROCM. Diffusion-weighted MRI sequence is useful in demonstrating optic nerve ischemia that would otherwise seem normal on other sequences. 4. 5. 6. 7. STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: A. L. Chaulk, T. H. Do, E. P. Supsupin, M. B. Bhattacharjee, K. Richani, and O. O. Adesina; b. Acquisition of data: A. L. Chaulk, T. H. Do, and M. B. Bhattacharjee; c. Analysis and interpretation of data: A. L. Chaulk, T. H. Do, E. P. Supsupin, M. B. Bhattacharjee, K. Richani, and O. O. Adesina. Category 2: a. Drafting the manuscript: A. L. Chaulk, T. H. Do, and O. O. Adesina; b. Revising it for intellectual content: A. L. Chaulk, T. H. Do, E. P. Supsupin, M. B. Bhattacharjee, K. Richani, and O. O. Adesina. Category 3: a. Final approval of the completed manuscript: A. L. Chaulk, T. H. Do, E. P. Supsupin, M. B. Bhattacharjee, K. Richani, and O. O. Adesina. 8. 9. 10. 11. REFERENCES 1. Mathur S, Karimi A, Mafee MF. 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