Horner Syndrome Due To Internal Carotid Artery Dissection With Normal Vascular Imaging: A Radiological Conundrum

Clinical Correspondence Section Editors: Robert Avery, DO Karl C. Golnik, MD Caroline Froment, MD, PhD An-Gour Wang, MD Horner Syndrome Due To Internal Carotid Artery Dissection With Normal Vascular Imaging: A Radiological Conundrum Sasha A. Mansukhani, MBBS, Laurence J. Eckel, MD, Kristi Y. Wu, MD, Mohamed B. Hassan, MD, Jon A. Van Loon, MD, John J. Chen, MD, PhD, M. Tariq Bhatti, MD A cute, painful Horner syndrome can be the presenting manifestation of an extracranial internal carotid artery (ICA) dissection, which is important to identify because of the high risk of stroke. Although catheter angiography has been considered for many years as the gold standard for the detection of cervical artery dissections, computed tomography angiography (CTA) and magnetic resonance angiography (MRA) are now considered to be nearly equivalent alternatives obliviating the need for angiography. We describe a patient who presented with a painful, partial left Horner syndrome and dysgeusia resulting from an extracranial ICA dissection with CTA and MRA within normal limits. Ultimately, the diagnosis was confirmed on the axial, T1-weighted, precontrast, fat-suppressed MRI. This case highlights the fact that ICA dissection may not be associated with substantial luminal narrowing and therefore undetectable on CTA or MRA. We also review the regional skull base neuroanatomy as it pertains to the intimate relationship between the ICA, oculosympathetic pathway, and glossopharyngeal nerve. One week before presentation, a 63-year-old man developed pain that localized to the left eye and worsened over a few days. He also described a sensation of bitter taste 1 day before presentation. There was no history of neck trauma or manipulation. Visual acuity was 20/20 in the right eye and 20/25 in the left eye. There was 2 mm of left upper eyelid ptosis. The left pupil was 2.5 mm smaller than the right, with the anisocoria more pronounced in the dim light (Fig. 1A). The rest of the anterior segment and retinal examination was unremarkable. There was no facial anhidrosis. Apraclonidine (1.0%) eye drop test resulted in resolution of Departments of Ophthalmology (SAM, KYW, MBH, JJC, MTB) and Radiology (LJE), Mayo Clinic College of Medicine, Rochester, Minnesota; Department of Psychiatry (JAVL), St. Elizabeth’s Medical Center, Wabasha, Minnesota; and Department of Neurology (JJC, MTB), Mayo Clinic College of Medicine, Rochester, Minnesota. Supported by Mayo Foundation. The authors report no conflicts of interest. Address correspondence to M. Tariq Bhatti, MD, Department of Ophthalmology, Mayo Clinic, 200 1st Street SW, Rochester, MN 55905; E-mail: [e-mail] e186 the ptosis and reversal of the anisocoria (Fig. 1B). CTA performed the same day was normal (Fig. 2A). The next day, he underwent MRI and MRA with contrast. The MRA was read as normal (Fig. 2B); however, the axial, precontrast, fat-suppressed T1-weighted images clearly showed a left ICA dissection (Fig. 2C). He was started on aspirin and clopidogrel for stroke prophylaxis. We present a case of an ICA dissection, presenting as an acute, painful, partial Horner syndrome that would have gone unrecognized if only a CTA and/or MRA had been performed. Although there is no universal standardized imaging protocol for Horner syndrome, many recommendations have been published (1). Because of its immediate availability, in most situations, CTA is often the first imaging modality to be performed. CTA has a 64%–100% sensitivity of detecting an ICA dissection (2). However, if the dissection does not narrow the lumen of the vessel, it may not be detectable on CTA or MRA as in our case. In such situations, the precontrast, axial, fat-suppressed T1-weighted MRI must be carefully reviewed. On MRI, the ICA dissection is seen as a crescent of T1 hyperintensity within the vessel wall (crescent sign) because of the presence of methemoglobin from the degrading blood. An acute intramural hematoma may however be isointense on T1- and T2-weighted imaging within the first 48 hours (3). Although the sensitivity of MRI/MRA has been reported to be similar to CTA (50%–100%), newer techniques such as high magnetic field strength, bolus timing, 3-dimensional acquisition, and use of fat suppression were not consistently reflected in these earlier studies (2). These newer postprocessing techniques have increased the sensitivity of MRI/MRA. This is especially true for ICA dissections compared with vertebral artery dissections. The third edition of the International Classification of Headache Disorders notes that it may be necessary to obtain more than one imaging technique (e.g., CTA, MRA, cervical MRI with fat suppression, duplex ultrasonography, and conventional angiography) since any one of them alone can be normal. Previous studies have described targeted imaging based on the localization features of the Horner pupil: MRI brain ±MRA head for a first-order neuron lesion, and computed Mansukhani et al: J Neuro-Ophthalmol 2021; 41: e186-e188 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Clinical Correspondence FIG. 1. A. External photograph—left upper eyelid ptosis with pupillary miosis. B. External photograph—resolution of the ptosis and reversal of the anisocoria 45 minutes after instillation of apraclonidine in both eyes, which confirmed a left Horner syndrome. C. Illustration of normal anatomy of the skull base as it pertains to the internal carotid artery (ICA), oculosympathetic trunk, and glossopharyngeal nerve. D. ICA dissection associated with an increase in the diameter of the vessel resulting in compression of the surrounding neural structures. Note that in this case, there is no narrowing of the ICA. tomography (CT)/CTA or MRI/MRA from lung apices to orbit for second- or third-order neuron lesions. For an isolated Horner syndrome without localizing signs, it is recommended that the entire oculosympathetic pathway (hypothalamus to lower cervical-upper thoracic spine) be imaged with either CT/CTA or MRI/MRA (1). Traditionally, topical cocaine drops have been used to confirm or refute the clinical diagnosis of a Horner pupil. However, since its introduction in 2000, apraclonidine has been shown to be an excellent alternative drop test. In fact, apraclonidine has recently been reported to be more sensitive than cocaine (93% vs. 40%, respectively) in FIG. 2. Computed tomography angiography (CTA), MRA, and MRI. A. CTA demonstrates normal luminal size and contour, without evidence of an internal carotid artery dissection (arrow). B. MRA showing the subtle irregularity of the left internal carotid artery (arrow), within normal limits. C. MRA volume rendered image demonstrating no abnormality at the site of dissection (arrow). D. Precontrast, fat-saturated, axial T1-weighted MRI depicting the “crescent sign” indicating dissection of the left internal carotid artery. MRA, magnetic resonance angiography. Mansukhani et al: J Neuro-Ophthalmol 2021; 41: e186-e188 e187 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Clinical Correspondence confirming the diagnosis of a Horner pupil (4). Apraclonidine is a weak a1 agonist and relies on denervation supersensitivity for pupillary dilation. The test may be falsely negative within the first few hours to days of onset of the Horner pupil, although the exact timing of the supersensitivity is unknown (4). In infants less than 6 months of age, apraclonidine can cause respiratory depression due to immaturity of the blood–brain barrier. In our patient, the dysgeusia localized the lesion just before the ICA entering the carotid canal. The 3 cranial nerves responsible for taste are the facial nerve, glossopharyngeal nerve and vagus nerve. The third-order oculosympathetic neurons travel along the common carotid and then the ICA. Just under the ramus of the mandible, the glossopharyngeal nerve crosses beneath the ICA. Enlargement of the ICA compresses both the oculosympathetic fibers as well as the glossopharyngeal nerve causing a Horner pupil and dysgeusia, respectively (Fig. 1C, 1D) (5). The enlarging intramural hematoma causes external compression of the surrounding neural structures, but it is the luminal e188 narrowing and formation of an intraluminal thrombus that is the nidus for a cerebral stroke. CTA has often been the test of choice when an acute ICA dissection is suspected due to widespread availability, speed of scan, and high reported sensitivity. The case presented in this report highlights the importance of obtaining a precontrast, cervical MRI with fat suppression in all patients suspected of harboring an ICA dissection if the CTA is normal. REFERENCES 1. Chen Y, Morgan ML, Barros Palau AE, Yalamanchili S, Lee AG. Evaluation and neuroimaging of the Horner syndrome. Can J Ophthalmol. 2015;50:107–111. 2. Hakimi R, Sivakumar S. Imaging of carotid dissection. Curr Pain Headache Rep. 2019;23:2. 3. Patel RR, Adam R, Maldjian C, Lincoln CM, Yuen A, Arneja A. Cervical carotid artery dissection: current review of diagnosis and treatment. Cardiol Rev. 2012;20:145–152. 4. Bremner F. Apraclonidine is better than cocaine for detection of horner syndrome. Front Neurol. 2019;10:55. 5. Bhatti MT, Schmalfuss I. Dysgeusia and painful Horner’s syndrome from an internal carotid artery dissection: radiological-anatomical correlation. Acta Ophthalmol Scand. 2002;80:562–564. Mansukhani et al: J Neuro-Ophthalmol 2021; 41: e186-e188 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.