Petrositis

Petrositis (petrous apicitis) is infection of the pneumatised air cells in the petrous apex of the temporal bone, usually as an extension of acute or chronic otitis media or mastoiditis. It risks osteomyelitis, meningitis, abscess and cranial nerve palsies.

It is now rare because of antibiotics, with perhaps 1 in 100,000 cases of otitis media, but it is easily missed. Only about a third of people have a pneumatised petrous apex. The commonest organisms are Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus pneumoniae and anaerobes.

Pathophysiology.

Infection spreads along air cell tracts or through bone and thrombophlebitic vessels to the apex. Pus is trapped by narrow channels, causing local pain and irritation of the trigeminal ganglion and abducens nerve in Dorello canal.

Persistent ear discharge, deep retro orbital or temporal pain, fever, headache and sometimes diplopia from sixth nerve palsy (Gradenigo triad). Facial weakness, vertigo and hearing loss may occur.

Red flags.

• Diplopia.
• Neck stiffness, confusion or seizures.
• Facial palsy.
• Sigmoid or cavernous sinus thrombosis signs.

CT of the temporal bone shows opacification and bone destruction of the petrous apex. Magnetic resonance imaging with contrast shows enhancement, abscess, meningeal enhancement and venous thrombosis. Send blood cultures, inflammatory markers and a swab of any discharge. Lumbar puncture is done when meningitis is suspected, after imaging.

Differential diagnosis.

• Cholesterol granuloma.
• Petrous apex cyst (mucocele).
• Skull base osteomyelitis.
• Chordoma or chondrosarcoma.
• Metastasis.
• Meningioma.

Give high dose intravenous antibiotics that reach the central nervous system and drain the middle ear and mastoid (myringotomy with tube, mastoidectomy). Surgical drainage of the petrous apex (transcanal, transmastoid or endoscopic) is done for abscess, bone destruction, or failure to improve after 48 to 72 hours of antibiotics.

• Ceftriaxone: 2 g IV every 12 hours; maximum 4 g daily; usually 4 to 6 weeks in total (IV for the first 2 to 4 weeks); monitor renal function, liver tests, blood counts and rash; no routine renal adjustment, and avoid with calcium infusions in neonates.
• Metronidazole: 500 mg IV or orally every 8 hours with ceftriaxone for the same duration; maximum 1.5 g daily; monitor neuropathy and liver tests; reduce to 500 mg every 12 hours in severe hepatic impairment.
• Vancomycin (added for suspected MRSA): load 25 to 30 mg/kg IV, then 15 to 20 mg/kg every 8 to 12 hours; target area under the curve 400 to 600; monitor levels and creatinine; extend the interval in renal impairment.
• Piperacillin-tazobactam (replace ceftriaxone and metronidazole if Pseudomonas is isolated): 4.5 g IV every 6 hours; maximum 18 g daily; monitor renal function and blood counts; reduce for creatinine clearance under 40 mL/min.

Anticoagulate venous sinus thrombosis by specialist decision. Dexamethasone is given only for meningitis (10 mg IV every 6 hours for 4 days, started before or with the first antibiotic dose).

Monitoring. Daily neurological examination, weekly inflammatory markers and imaging at 4 to 6 weeks.

Referral and escalation. ENT and neurosurgery urgently; critical care for sepsis.

Special groups. Children need weight based dosing: ceftriaxone 100 mg/kg daily (maximum 4 g).