Metastatic lesions, pinealomas, acoustic neuromas, parasellar and tentorial meningiomas, and gliomas of the midbrain and cerebellum have been associated with trochlear palsy. In many of these cases, the fourth nerve palsy was due to raised intracranial pressure, not direct compression. Schwannoma of the ocular motor nerves are rare since they have a propensity for sensory nerves. As elsewhere, these tumors are well-encapsulated solitary proliferations of Schwann cells. They are devoid of nerve fibers, as present in neurofibromas.
Malignant transformation is very rare.
Surgical removal is usually associated with worsening or persistence of fourth nerve palsy. Periodic follow-up is advisable, especially in patients with neurofibromatosis. Prismatic correction - Prism can be very helpful, especially if the deviation is nearly comitant and associated with small torsional components. Strabismus surgery - Numerous surgical schemes have been suggested, including Knapp, 1974. MR imaging of primary trochlear nerve neoplasms.