2007 May 08, Tuesday

[Sanju]

Today's MCQ will be answered tomorrow.

Yesterday's MCQ was: Nerve with longest intracranial course is:
a) Trochlear
b) Abducen
c) Trigeminal
d) Occulomotor
The correct answer is a) Trochlear

[hydatidcyst]

Is it really trochlear or is it abducens. I had studied the longest intracranial CN as VI. But when I saw the answer today, I searched the net. Some say it is IV, some say it is VI. Which is it really ?

One site says : CN IV : it originates at the lower level of the midbrain and has the longest intracranial course of all cranial nerves. It travels via the cavernous sinus to innervate the superior oblique muscle. Each CN IV nerve nucleus innervates the opposite side. It is responsible for abduction and intorsion. Due to its long course the CN IV is very susceptible to trauma.

The other says : VI has the longest intracranial course. It arises from the pons-medulla junction, travels forward over the petrous temporal bone and traverses the cavernous sinus to reach the superior orbital fissure. Because of this long intracranial course, the nerve is subject to increased intracranial pressure (as for example, due to a tumor) which may result in bilateral paralyses of the lateral rectus muscles. This is often referred to as a false localizing sign since it focusses attention on the VI nerve but the basic etiology is a space-occupying lesion within the cranial cavity.

[Sanju]

As far as i have read trochlear nerve is the longest intracranial nerve with length of around 60mm.