Bilateral Trochlear Nerve Palsy as a Consequence of Cerebellar Medulloblastoma: Clinical and Pathological Findings in a Calf

A 1-month old female Holstein calf had not been able to stand since birth. Delivery was uncomplicated and no treatment had been administered before admission. On physical examination, the calf had slightly decreased body condition, but was bright and alert. The calf was in lateral recumbency with spastic extension of all four limbs and opisthotonus. If positioned in left lateral recumbency, the calf raised its head, which fell immediately to the ground after rotation of the neck. The calf made no attempt to raise its head when lying in right lateral recumbency. Attempts to passively position the calf in a quadrupedal stance or in sternal recumbency were unsuccessful. Despite the lateral recumbency, the calf was able to suckle. A thorough neurologic examination was carried out. Mental status and consciousness were considered normal. Because of recumbency, postural reactions could not be tested. The menace response was absent in the right eye and present in the left eye. In both eyes, the medial end of the pupil was rotated dorsally. This dorsomedial rotation of the eyes was not affected by changes in the position of the head. Moreover, incomitant strabismus (i.e., degree of misalignment of the eyes varying with the position of the head) was evident, particularly in left lateral recumbency, characterized by an upward deviation of the visual axis of the left eye (hypertropia) and inward deviation of the visual axis of the right eye (esotropia, Fig. 1). Other routine tests for evaluation of the cranial nerves were normal as were the spinal reflexes. Mild neutrophilic leukocytosis was present on the CBC. On the basis of the clinical and neurologic findings, the tentative anatomical diagnosis was a congenital lesion, located at the level of the right side of the cerebellum with bilateral involvement of the trochlear nerve (cranial nerve [CN] IV) and possibly, but less likely, of the other nerves innervating the extraocular muscles (oculomotor nerve, CN III and abducent nerve, CN VI). The most likely differential diagnoses were malformations (e.g., dermoid cyst in the caudal fossa compressing the cerebellum) and embryonal tumors (e.g., medulloblastomas directly or indirectly involving the cerebellum). Bacterial meningoencephalitis, mainly affecting the caudal fossa, also was considered but excluded by the results of cerebrospinal fluid (CSF) evaluation. Lumbosacral CSF samples were analyzed and showed albuminocytologic dissociation, the total proteins being 113 mg/dL (reference range, <30 mg/dL) and the total nucleated cell count 9 cells/ll (reference range, <10 cells/lL). Because of the poor prognosis, the calf