Square Wave Jerks and Macrosaccadic Oscillations in a Patient with a Cerebellar Tumor

This is a 40-year-old man who developed severe headaches, confusion, and gait imbalance which led to neuroimaging which demonstrated a midline cerebellar mass with compression of the fourth ventricle and obstructive hydrocephalus. He underwent a suboccipital craniectomy for resection of the mass, and pathology was consistent with a hemangioblastoma. The video shown here was taken 4 months after initial presentation. Most notable on his ocular motor exam was gaze-evoked nystagmus (with a downbeat component) with rebound nystagmus, and saccadic hypermetria in all directions. In straight ahead gaze, while there was no spontaneous nystagmus, saccadic intrusions were apparent. At baseline, there were small horizontal saccades that would take the eyes away from the visual target for brief periods, consistent with square wave jerks (SWJ). While SWJ normally occur, especially as people age, the frequency was much more in this patient than what would be expected in a 40-year-old. SWJ are also common in cerebellar disease, as in this patient. These were visually asymptomatic. Intermittently, there were also larger amplitude oscillations that would cause the eyes to move back and forth around the visual target, consistent with macrosaccadic oscillations. Macrosaccadic oscillations may be seen in patients with saccadic hypermetria, and are thought to be related to lesions involving the (midline) cerebellar fastigial nuclei or their outputs from the superior cerebellar peduncle to excitatory/inhibitory burst neuron pairs.