Cavernous Sinus – Anatomy · FCPS Part 1

💡Cavernous Sinus Anatomy & Pathology

Feature	FCPS answer	High-yield point
Location	On either side of the body of the sphenoid bone and sella turcica	Paired dural venous sinuses
Medial relation	Pituitary gland and sphenoid air sinus	Sella turcica contains the pituitary
Contents within sinus	ICA + CN VI	CN VI is particularly vulnerable
Lateral wall — superior to inferior	CN III → CN IV → V₁ → V₂	Remember: 3, 4, 1, 2
CN VI position	Inferolateral to ICA, within sinus proper	Not in the lateral wall
ICA	Surrounded by sympathetic nerve plexus	Injury may cause carotid-cavernous fistula
Venous drainage	Superior and inferior petrosal sinuses	Connects with other intracranial venous pathways

Clinical presentation / question	Correct answer	Explanation
First cranial nerve commonly affected in cavernous sinus thrombosis	CN VI (abducens)	Runs freely within the sinus
Patient cannot abduct the eye	CN VI palsy	Unopposed medial rectus causes medial deviation
Ptosis, dilated pupil and eye deviated down and out	CN III palsy	Oculomotor nerve involvement
Loss of forehead sensation	V₁ involvement	Ophthalmic division supplies the forehead and cornea
Loss of sensation over cheek and upper lip	V₂ involvement	Maxillary division
Infection spreads from the danger area of the face	Facial/angular → ophthalmic veins → cavernous sinus	These venous pathways are valveless
Pulsatile exophthalmos, chemosis and orbital bruit after trauma	Carotid-cavernous fistula	Abnormal communication between ICA and cavernous sinus
Horner syndrome associated with cavernous sinus pathology	Sympathetic plexus involvement	May cause miosis, mild ptosis and anhidrosis
Pituitary tumour extending laterally	Cavernous sinus involvement	May compress CN III, IV, V₁, V₂ and VI
Corneal reflex — afferent limb	V₁	Nasociliary branch
Corneal reflex — efferent limb	CN VII	Orbicularis oculi closes the eyelids