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Petrous apicitis is a suppurative infection of the petrous apex of the temporal bone, typically arising as a complication of acute or chronic otitis media, especially in patients with pneumatized petrous apices. It may lead to cranial nerve involvement, including Gradenigo syndrome.

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Anatomy

The petrous apex lies between the inner ear and clivus, forming part of the petrous temporal bone.
It may be:
- Pneumatized (air cells – vulnerable to infection)
- Sclerotic (solid bone – less likely involved)
- Diploic (marrow-filled)

Etiopathogenesis

Infection spreads from the middle ear and mastoid into the pneumatized petrous apex via air cell tracts.
Leads to osteitis, bone erosion, and inflammatory extension into adjacent neurovascular structures.

Clinical Features

Symptom	Mechanism
Persistent ear discharge	Chronic otitis media
Retro-orbital or facial pain	Trigeminal nerve (CN V) irritation
Diplopia (lateral rectus palsy)	CN VI (abducens) palsy due to involvement of Dorello’s canal
Fever, headache, malaise	Systemic infection
Vertigo, tinnitus	If inner ear affected
Meningitis or cavernous sinus thrombosis	Rare but serious complications

Gradenigo syndrome:

Classic triad: This syndrome occurs when infection extends to Meckel’s cave and Dorello’s canal.

Otorrhea (chronic otitis media)
Deep facial pain (trigeminal nerve involvement)
Diplopia (due to CN VI palsy from Dorello’s canal involvement)

Radiology

Modality	Imaging features
CT	• Erosive changes of petrous apex: Decreased trabeculation or cortical breach
• Asymmetric opacification of petrous air cells
• Erosion of bony labyrinth, facial canal
• Gradenigo syndrome: Extension to Meckel’s cave / Dorello’s canal
MR	• T1: Hypointense marrow signal in petrous apex (normally fatty)
• T2: Hyperintense in fluid-filled infected apex
• Post-contrast: Enhancement of petrous apex, dural enhancement, Meckel’s cave involvement
• DWI: May help differentiate from abscess or cholesteatoma