CTA revealed a focal linear filling defect in the right midinternal carotid artery, likely related to an internal carotid artery vascular flap. There was no evidence of proximal intracranial occlusive disease. MRI revealed a linear area of high-intensity signal projecting over the mid and distal right internal carotid artery lumen (Figure 2A).
Imaging suggested an internal carotid artery dissection, and the patient was admitted to the hospital for observation for 4 days. During this time, the patient was instructed to continue taking 81mg aspirin daily and to begin taking 75 mg clopidogrel bisulfate daily to prevent a cerebrovascular accident. Once stability was established, the patient was discharged with instructions to follow up with neurology and neuro-ophthalmology.
Discussion
Anisocoria is defined as a difference in pupil sizes between the eyes.1 This difference can be physiologic with no underlying pathology as an etiology of the condition. If underlying pathology causes anisocoria, it can result in dysfunction with mydriasis, leading to a more miotic pupil, or it can result from issues with miosis, leading to a more mydriatic pupil.1
To determine whether anisocoria is physiologic or pathologic, one must assess the patient’s pupil sizes in dim and bright illumination. If the difference in the pupil size is the same in both room illuminations (ie, the anisocoria is 2 mm in both bright and dim illumination, pupillary constriction and dilation are functioning normally), then the patient has physiologic anisocoria.1 If anisocoria is different in bright and dim illumination (ie, the anisocoria is 1 mm in bright and 3 mm in dim settings or 3 mm in bright and 1 mm in dim settings), the condition is related to pathology. To determine the underlying pathology of anisocoria in cases that are not physiologic, it is important to first determine whether the anisocoria is related to miotic or mydriatic dysfunction.1
If the anisocoria is greater in dim illumination, this suggests mydriatic dysfunction and could be a result of damage to the sympathetic pupillary pathway.1 The smaller or more miotic pupil in this instance is the pathologic pupil. If the anisocoria is greater in bright illumination, this suggests miotic dysfunction and could be a result of damage to the parasympathetic pathway.1 The larger or more mydriatic pupil in this instance is the pathologic pupil. Congenital abnormalities, such as iris colobomas, aniridia, and ectopic pupils, can result in a wide range of pupil sizes and shapes, including miotic or mydriatic pupils.1