Case report Intraventricular Silicone Oil Migration Resembling Hemorrhagic Complication in a Patient with Ischemic Stroke Receiving Antithrombotic Therapy Rui Shimazaki, MD, Marie Tsunogae, MD, and Masayuki Ueda, MD, PhD We report herein a case of intraventricular silicone oil migration, a rare complication of intraocular silicone oil tamponade, mimicking a hemorrhage during antithrombotic therapy for ischemic stroke. A 62-year-old male patient with a history of diabetic retinopathy was admitted for right hemiparesis and dysarthria. Brain magnetic resonance imaging on admission showed an acute left-sided ventral medullary infarction, and antithrombotic therapy was started. Head computed tomography done on the next day after admission showed an area of high-density resembling a hematoma in the lateral ventricle. Additional magnetic resonance imaging in the supine and lateral recumbent positions confirmed migration of the lesion within the ventricles by position, indicating intraventricular silicone oil migration. Several facilities in Japan perform magnetic resonance imaging instead of computed tomography as the first step in assessing stroke in the emergency clinical setting. While the silicone oil used in internal tamponade appears high-density on computed tomography, it does not register as an abnormality on diffusionweighted imaging, thus creating a pitfall to diagnosis based on this modality. Key Words: MRI first clinical practice—Intraventricular migration of silicone oil—Hemorrhage—Silicone oil tamponade—Diabetic retinopathy © 2020 Published by Elsevier Inc. Introduction Silicone oil (SiO) tamponade is widely used to treat retinal detachment and diabetic retinopathy.1 Intraventricular migration of silicone oil (IVM-SiO) is a rare and late complication of this treatment.2-3 We reported herein a case of IVM-SiO mimicking intraventricular hemorrhage on CT during antithrombotic therapy for ischemic stroke. Several facilities apply magnetic resonance imaging (MRI) first stroke practice, and SiO resembling a hemorrhage on CT can be a pitfall. From the Department of Neurology and Stroke Medicine, Tokyo Metropolitan Tama Medical Center, 2-8-29 Musashidai, Fuchu, Tokyo 183-8524, Japan. Received September 24, 2020; revision received November 27, 2020; accepted December 2, 2020. Corresponding author. E-mail: rui_shimazaki@tmhp.jp. 1052-3057/$ - see front matter © 2020 Published by Elsevier Inc. https://doi.org/10.1016/j.jstrokecerebrovasdis.2020.105527 Case report A 62-year-old male patient with a two-day history of right hemiparesis and dysarthria was admitted to our hospital. He had a history of diabetes and blindness in the right eye due to diabetic retinopathy but had defaulted from diabetes treatment for one year. He received some treatment for the right-sided diabetic retinopathy, but did not remember the details. Laboratory tests showed hyperglycemia. Brain MRI on admission showed an acute, leftsided, medullary infarction (Fig. 1A). Antithrombotic therapy was started, but the neurological symptoms deteriorated. Head CT on the next day showed high-density in the lateral ventricle (Fig. 1B). A hemorrhagic complication of antithrombotics was initially suspected, but a review of the neuroimaging findings revealed an abnormal right eyeball and optic nerve (Fig. 1C-D) and intraventricular lesions (Fig. 1E). These findings indicated the ventricular lesions were IVM-SiO rather than hemorrhage. An inquiry to his previous physician disclosed that he had undergone right-sided SiO tamponade but had Journal of Stroke and Cerebrovascular Diseases, Vol. 30, No. 2 (February), 2021: 105527 1 R. SHIMAZAKI ET AL. 2 Figure 1. (A): Diffusion-weighted imaging on admission. Note acute infarction in the left ventral medulla oblongata. The eyeballs do not show abnormal signal intensity. (B-C): Non-contrast cranial X-ray computed tomography (CT) on the day after admission. First CT to be performed after admission. Note the high-density lesion mimicking a hemorrhage in the right lateral ventricle (white arrow head). Areas of high-densities can be seen in the right-side eyeball and optic nerve (white arrows). (D-E): Fluid-attenuated inversion recovery image at admission Image at the same slice level as in Fig. 1A, displaying high-signal intensity in the right eyeball and optic nerve (gray arrows). Note the nearly symmetrical, high-signals in the bilateral anterior horn of the lateral ventricles (black arrow heads), apparently resembling periventricular caps. (F-H): T2-weighted imaging on day 18 after admission Image data acquisition was performed with the patient in the supine (F-G) and lateral recumbent positions (H). Right eyeball showed high to low signal intensities from the top (white broken arrow). Brain image in the supine position (G) displayed areas of varying signal intensity similar to that of the right eyeball in the left anterior horn of lateral ventricle (black arrow), which moved within the ventricle (black broken arrow) when the patient was in the lateral recumbent position (H), indicating intraventricular silicone oil. failed to be present for its removal. Follow-up MRI done with the patient in the supine and lateral recumbent positions confirmed the migration of the lesion within the ventricles by position (Fig. 1GE-HG). Based on these findings, IVM-SiO was finally diagnosed. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could appear to influence the work reported in this paper. Financial disclosures Discussion Although the precise mechanism of IVM-SiO remains unclear, deep optic cup and optic nerve degeneration resulting from elevated intraocular pressure may create communication between the subarachnoid space of the optic nerve and the intracranium, allowing the SiO to enter the ventricles.4 Intraocular SiO reportedly shows high-density on CT5 but does not appear as abnormal on diffusion-weighted imaging (DWI).6 The high-density around the optic nerve on CT in the patient suggested that the SiO flowed along optic nerve. Japan has the largest the number of MRI scanners per capita worldwide.7 Therefore, MRI first clinical practice is often done in acute stroke management. However, in the emergency setting, imaging findings besides those of DWI may be overlooked. Neurologists should be aware of the IVM-SiO when assessing stroke, especially in the MRI first setting. Rui Shimazaki- Has no disclosures Marie Tsunogae- Has no disclosures Masayuki Ueda- Has no disclosures Credit author statement Rui Shimazaki: Conceptualization, investigation, drafting of the manuscript Marie Tsunogae: Supervising conceptualization Masayuki Ueda: Supervising conceptualization, writing, reviewing, and editing the manuscript References 1. Azan SP, Scott IU, Flynn Jr HW, et al. Silicone oil in the repair of complex retinal detachments: a prospective observational multicenter study. Ophthalmology 1998;105(9):1587-1597. 2. Filippidis AS, Conroy TJ, Maragkos GA, et al. Intraocular silicone oil migration into the ventricles resembling intraventricular hemorrhage: case report and review of the literature. World Neurosurg 2017;102:695. INTRAVENTRICULAR SILICONE OIL MIGRATION IN STROKE 3. Mathis S, Boissonnot M, Tasu JP, et al. Intraventricular silicone oil: a case report. Medicine (Baltimore) 2016;95:e2359. 4. Chang C, Chang H, Toh CH. Intraventricular silicone oil. 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