Describe otogenic meningitis, extradural and subdural abscess.

Otogenic Meningitis

• Otogenic meningitis is inflammation of the leptomeninges secondary to middle ear or mastoid infection.
• It is the commonest intracranial complication of otitis media, and is the commonest cause of death from ear disease in children.
• Routes — in acute otitis media, chiefly through preformed pathways (the oval and round windows, the cochlear aqueduct, congenital dehiscences and the petrosquamous suture) and by haematogenous spread; in chronic disease, by bone erosion from cholesteatoma, by extension from an extradural or brain abscess, or through a labyrinthine fistula

Extradural and Subdural Abscess

• Extradural (epidural) abscess is a collection of pus between the bone and the dura, and is the commonest intracranial complication after meningitis
• It arises by direct bone erosion, of the tegmen (giving a middle fossa collection) or of the sinus plate (a perisinus abscess)
• The difficulty IS that IT IS frequently silent, and is most often discovered incidentally at mastoid surgery when granulation tissue and pus are found on exposed dura
• When it does declare itself — persistent deep-seated headache on the affected side; low-grade fever; malaise; and, characteristically, profuse pulsatile discharge from the ear that relieves the headache as the abscess drains
• Investigation — contrast CT or MRI, showing a lentiform collection with dural enhancement, and bony erosion on temporal bone CT
• Treatment — intravenous antibiotics and surgical drainage.
• Subdural abscess (empyema) lies between the dura and the arachnoid, and is far more dangerous because there is no anatomical barrier to its spread over the cerebral convexity
• It is rarer but has a much higher mortality, and is more often sinogenic than otogenic
• Features — rapid deterioration, with high fever, severe headache, meningism, seizures (which are common and often focal), rapidly progressive focal neurological deficit and falling conscious level — the combination of meningeal and focal signs progressing quickly is characteristic
• Investigation — urgent contrast CT or, preferably, MRI.
• Treatment — urgent neurosurgical drainage by burr holes or craniotomy, high-dose intravenous antibiotics, anticonvulsants, and management of raised intracranial pressure; with mastoid surgery to the source once stabilised
• Scan before you tap; a coexisting abscess or raised pressure turns a lumbar puncture into coning
• Neck stiffness is absent in infants, who show a bulging fontanelle, high-pitched cry and refusal of feeds instead
• Give dexamethasone with or before the first antibiotic in pneumococcal meningitis, which reduces deafness and neurological sequelae
• Test hearing early after meningitis; labyrinthine ossification begins within weeks and can make implantation impossible
• Recurrent meningitis means a persistent defect — a CSF fistula, a Mondini malformation or an old temporal bone fracture
• Low CSF glucose distinguishes bacterial disease, below about forty per cent of the blood level, with raised polymorphs and protein
• Operate on the ear once the patient is stable; leaving the source means the meningitis returns
• Chronic disease grows Gram-negatives and anaerobes, quite unlike the pneumococcus and haemophilus of acute otitis media
• Extradural abscess is often silent, and is most commonly discovered incidentally during mastoid surgery
• Pulsatile discharge that relieves headache suggests an extradural abscess draining into the ear
• Expose healthy dura on all sides when draining an extradural abscess, and do not incise the dura itself
• Subdural empyema spreads unchecked over the convexity, having no anatomical barrier.
• Meningeal plus rapidly progressive focal signs suggest subdural empyema rather than meningitis alone
• MRI beats CT for a thin subdural collection, which plain CT may miss entirely at the convexity
• Subdural empyema is more often sinogenic than otogenic, so the paranasal sinuses must be assessed as well
• Start antibiotics before the culture returns; delay while awaiting results costs lives in meningitis
• Projectile vomiting without nausea indicates raised intracranial pressure rather than a gastrointestinal cause
• Seizures in subdural empyema are common and focal, and anticonvulsant cover is given prophylactically