Paraflocculus (Tonsillar) Ocular Motor Syndrome and Dysmetria in a Chiari Malformation - Pre and Post-Operative Exams

𝗢𝗿𝗶𝗴𝗶𝗻𝗮𝗹 𝗗𝗲𝘀𝗰𝗿𝗶𝗽𝘁𝗶𝗼𝗻: This is a 25-year-old woman presenting with 6 months or progressive imbalance, binocular vertical diplopia, and occipital headaches, which were brought on or aggravated by coughing or sneezing. Examination demonstrated hyperreflexia in the arms and legs with sustained clonus at the ankles and Babinski reflexes bilaterally in addition to gait and limb ataxia. There were a variety of ocular motor abnormalities as well (see below). Contrast-enhanced MRI demonstrated peg-like cerebellar tonsils extending 2.9 cm below the foramen magnum (more tonsillar herniation on the right), and flattening of the dorsal medulla (right>left). There was also syringohydromyelia of the cervical and proximal thoracic spinal cord with cord parenchymal thinning. Taken together, this was consistent with a Chiari type I malformation. ; Visual exam, eyelids, and pupils were normal. While there was bilateral tonsillar herniation, it was worse on the right. In fact, the following findings were suggestive of a right paraflocculus (tonsillar) ocular motor syndrome: 1) weak right-beating (ipsilateral) spontaneous nystagmus (not seen in the video); 2) strong and (slightly) asymmetric right more than left gaze-evoked nystagmus (ipsilateral>contralateral) - in her case, there was also downbeat and torsion in lateral and down/lateral gaze (perhaps due to bilateral paraflocculus compression); 3) impaired smooth pursuit and vestibulo-ocular reflex suppression (VORS) toward the right (ipsilateral); 4) there was also a fairly comitant right hypertropia (a skew deviation), ocular counterroll (top poles toward the left ear), and subjective visual vertical tilt 5 degrees to the left with the bucket test - taken together, this was consistent with a contraversive partial ocular tilt reaction (no clear head tilt). Head impulse test was normal. There was also saccadic dysmetria with hypermetria to the right and hypometria to the left (limb ataxia was worse on the right side as well). It was felt that this was due to compression of the right inferior cerebellar peduncle, affecting climbing fibers from left inferior olive to right dorsal vermis. ; She underwent suboccipital craniectomy and C1 laminectomy, and when she was seen 6 months following surgery, all ocular motor findings had resolved with the exception of mild residual gaze-evoked nystagmus. 𝗡𝗲𝘂𝗿𝗼-𝗼𝗽𝗵𝘁𝗵𝗮𝗹𝗺𝗼𝗹𝗼𝗴𝘆 𝗮𝗻𝗱 𝗡𝗲𝘂𝗿𝗼-𝗼𝘁𝗼𝗹𝗼𝗴𝘆 𝗧𝗲𝘅𝘁𝗯𝗼𝗼𝗸 𝗟𝗲𝗴𝗲𝗻𝗱: This is a 25-year-old woman presenting with 6 months or progressive imbalance, binocular vertical diplopia, and occipital headaches, which were brought on or aggravated by coughing or sneezing. Examination demonstrated hyperreflexia in the arms and legs with sustained clonus at the ankles and Babinski reflexes bilaterally in addition to gait and limb ataxia. There were a variety of ocular motor abnormalities as well (see below). Contrast-enhanced MRI demonstrated peg-like cerebellar tonsils extending 2.9 cm below the foramen magnum (more tonsillar herniation on the right), and flattening of the dorsal medulla (right>left). There was also syringohydromyelia of the cervical and proximal thoracic spinal cord with cord parenchymal thinning. Taken together, this was consistent with a Chiari type I malformation. While there was bilateral tonsillar herniation, it was worse on the right. In fact, the following findings were suggestive of a right paraflocculus (tonsillar) ocular motor syndrome: 1) weak right-beating (ipsilateral) spontaneous nystagmus (not seen in the video); 2) strong and (slightly) asymmetric right more than left gaze-evoked nystagmus (ipsilateral>contralateral) - in her case, there was also downbeat and torsion in lateral and down/lateral gaze (perhaps due to bilateral paraflocculus compression); 3) impaired smooth pursuit and vestibulo-ocular reflex suppression (VORS) toward the right (ipsilateral); 4) there was also a fairly comitant right hypertropia (a skew deviation), ocular counterroll (top poles toward the left ear), and subjective visual vertical tilt 5 degrees to the left with the bucket test - taken together, this was consistent with a contraversive partial ocular tilt reaction (no clear head tilt). Head impulse test was normal. There was also saccadic dysmetria with hypermetria to the right and hypometria to the left (limb ataxia was worse on the right side as well). It was felt that this was due to compression of the right inferior cerebellar peduncle, affecting climbing fibers from left inferior olive to right dorsal vermis. She underwent suboccipital craniectomy and C1 laminectomy, and when she was seen 6 months following surgery, all ocular motor findings had resolved with the exception of mild residual gaze-evoked nystagmus. https://collections.lib.utah. edu/ark:/87278/s64r3f70