In cavernous sinus thrombosis, first nerve to be affected is: September 2012
**Core Concept**
Cavernous sinus thrombosis is a medical emergency characterized by the formation of a blood clot within the cavernous sinus, a group of veins located near the base of the brain. The cavernous sinus thrombosis can lead to the compression of adjacent cranial nerves, resulting in various neurological symptoms.
**Why the Correct Answer is Right**
The first nerve to be affected in cavernous sinus thrombosis is the IIIrd cranial nerve, also known as the oculomotor nerve. This is because the oculomotor nerve passes through the lateral wall of the cavernous sinus, making it the most susceptible to compression. The oculomotor nerve controls several important functions, including eye movement, pupil constriction, and eyelid opening.
**Why Each Wrong Option is Incorrect**
* **Option A:** Not specified.
* **Option B:** The IVth cranial nerve (trochlear nerve) is also susceptible to compression but is less likely to be affected first due to its location.
* **Option C:** The VIth cranial nerve (abducens nerve) is also at risk but is typically affected later in the course of the disease.
* **Option D:** The Vth cranial nerve (trigeminal nerve) is not typically involved in cavernous sinus thrombosis.
**Clinical Pearl / High-Yield Fact**
In cavernous sinus thrombosis, the oculomotor nerve palsy can present with ptosis (drooping eyelid), dilated pupil, and impaired eye movement. This clinical presentation is often referred to as "down and out" due to the characteristic ptosis and outward deviation of the eye.
**Correct Answer:** C.