What is the pathophysiology of congenital trochlear nerve palsy (fourth nerve palsy)?

Updated: Oct 08, 2019
  • Author: Zafar A Sheik, MD, MD; Chief Editor: Andrew G Lee, MD  more...
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A series of high-definition MRI studies by Yang et al have identified two etiologies of congenital trochlear nerve palsies, with the most common being congenital cranial dysinnervation syndrome. This syndrome was present in 73% of congenital trochlear nerve palsy cases and is characterized by absence of the trochlear nerve and secondary atrophy of the superior oblique muscle. The remaining 27% had a normal trochlear nerve and superior oblique muscle size, but an abnormal superior oblique tendon, which may explain the variations in superior oblique tendon laxity encountered surgically. [8, 9, 10]

Helveston, in a series of 36 congenital superior oblique palsy patients, found 33 abnormal superior oblique tendons. [16] The tendon may be abnormally lax, have an abnormal insertion, or be absent altogether.

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