Surgery chapters
Intracranial infections: meningitis, brain abscess and surgical site infection
The surgical side of CNS infection: post-traumatic and post-operative meningitis, CSF findings, brain abscess, subdural empyema, tuberculous lesions, neurocysticercosis, and infection after craniotomy or shunt surgery.
- Meningitis after head injury or neurosurgery is caused by skin and nasal organisms (Staph. aureus, gram-negative bacilli, Pseudomonas, pneumococcus); a CSF leak after skull base fracture is a major risk.
- A brain abscess presents like a growing mass (headache, seizures, focal deficit) with mild fever; CT shows a ring-enhancing lesion and diffusion-weighted MRI helps tell it from tumour; treat with drainage plus at least 6 weeks of antibiotics, and never do an LP.
- Neurosurgical wound and shunt infections need removal of infected hardware or bone flap, culture-guided antibiotics and later reconstruction.
On this page
Overview
The surgeon meets CNS infection in three ways:
- Meningitis after head injury, CSF leak or neurosurgery (and community meningitis that causes hydrocephalus).
- Focal pus: brain abscess and subdural or extradural empyema, which behave like expanding masses and need drainage.
- Surgical site infection: infected craniotomy wounds, bone flaps, shunts and drains.
Pakistan also sees many tuberculous lesions and neurocysticercosis. The medical treatment of community meningitis is covered in the medicine section; this chapter gives the surgical view.
Meningitis
What it is
Inflammation of the coverings (meninges) around the brain and cord, most often bacterial. Meningism = fever, headache, neck stiffness and photophobia; Kernig's sign positive. Bacterial meningitis can progress in hours to cerebral oedema, venous thrombosis and death.
Meningitis in surgical patients
| Setting | Usual organisms | Points |
|---|---|---|
| Basal skull fracture with CSF leak | Nasal commensals: pneumococcus, other gram-positive cocci, gram-negative bacilli | About 25% of patients with a CSF leak develop meningitis; recurrent meningitis suggests a hidden leak; repair the leak if it persists |
| After craniotomy, EVD or shunt | Staph. aureus, coagulase-negative staphylococci, Enterobacteriaceae, Pseudomonas | Onset often slower and less dramatic than community meningitis |
| Community acquired (adults) | Pneumococcus, meningococcus; Listeria in the elderly and immunocompromised | Medical emergency; may later cause hydrocephalus |
Diagnosis
- Blood cultures at once.
- CT head before LP if there is reduced consciousness, focal signs, papilloedema, seizures, or a recent head injury or operation.
- LP: CSF for microscopy and Gram stain, culture, protein and glucose (with a paired blood glucose), cell count, PCR.
- After neurosurgery, CSF is sampled from the EVD or shunt reservoir.
| CSF | Normal | Bacterial (pyogenic) | Viral | Tuberculous |
|---|---|---|---|---|
| Appearance | Crystal clear | Turbid/purulent | Clear | Clear or turbid, may form a "cobweb" clot |
| Main cells | Under 5 lymphocytes | Polymorphs (hundreds or more) | Lymphocytes | Lymphocytes |
| Protein | 0.2–0.4 g/L | High | Normal or mildly high | High (often very high) |
| Glucose (vs blood) | About 2/3 | Low (under half) | Normal | Low (under half) |
In TB meningitis the CSF shows lymphocytes, not polymorphs, and the protein rise and glucose fall are less extreme than in pyogenic meningitis. The Ziehl-Neelsen stain is often negative; send a large volume (20–30 mL) for culture and use PCR for a quicker answer.
Treatment
- Empirical antibiotics without delay, then adjust to culture:
- Community meningitis: a third-generation cephalosporin (cefotaxime or ceftriaxone), adding vancomycin where resistant pneumococci are common and ampicillin for Listeria cover in those over 50 or immunocompromised; dexamethasone with or just before the first antibiotic dose.
- Post-neurosurgical or post-traumatic meningitis: broad-spectrum cover for staphylococci and gram-negative bacilli including Pseudomonas (choice per local microbiology). Intraventricular antibiotics can be given through an EVD.
- Remove infected hardware (shunt, drain).
- Repair persistent CSF leaks and depressed or open fractures.
- Notify meningococcal disease and give contacts rifampicin or ciprofloxacin prophylaxis.
Recurrent bacterial meningitis (usually pneumococcal) points to a dural defect: an old skull base fracture with CSF leak, a dermal sinus, or a congenital defect. Look for and repair it.
Tuberculosis of the CNS
Spread is haematogenous from a lung focus. Highly relevant in Pakistan.
- TB meningitis: often young children; slow onset over weeks; cranial nerve palsies; CT shows thick basal meningeal enhancement; hydrocephalus (communicating, from basal exudate) is a common complication.
- Tuberculoma: firm granuloma behaving as a mass; may enhance as a ring or disc.
- Tuberculous abscess: tuberculoma with a large caseous centre, mainly in the immunocompromised.
- Miliary: many tiny tuberculomas.
- Treat with antituberculous therapy (plus steroids per guidelines); hydrocephalus may need a VP shunt or EVD. Follow the current national TB programme guidance, as regimens change.
Brain abscess
Sources and organisms
| Source | Typical organisms |
|---|---|
| Spread from sinuses, middle ear or mastoid (frontal lobe from frontal sinus; temporal lobe or cerebellum from ear) | Aerobic and anaerobic streptococci (Strep. anginosus/milleri group), Bacteroides, enterobacteria, staphylococci, Pseudomonas |
| Blood-borne (dental, lung, endocarditis, cyanotic heart disease with right-to-left shunt): often multiple, at the grey-white junction | Streptococci, Bacteroides |
| Penetrating injury or surgery | Staph. aureus, clostridia, enterobacteria |
| Immunocompromised (HIV) | Toxoplasma, fungi (Cryptococcus, Aspergillus), mycobacteria |
| Contaminated food | Pork tapeworm (neurocysticercosis), Toxoplasma |
In about a quarter of cases no source is found.
Classic exam pairings: frontal abscess ← frontal sinusitis; temporal lobe or cerebellar abscess ← chronic otitis media/mastoiditis; multiple abscesses ← endocarditis or cyanotic heart disease (e.g. tetralogy of Fallot).
Clinical features
- Like a growing mass lesion: headache, seizures, focal deficit, confusion, signs of raised ICP.
- Fever is often low grade or absent; blood inflammatory markers may be only mildly raised.
- Sudden worsening suggests rupture into the ventricles or herniation.
Investigations
- CT with contrast first. Early cerebritis = poorly defined low-density area. A mature abscess (about 2 weeks) = smooth, thin-walled ring-enhancing lesion with surrounding oedema.
- MRI with diffusion-weighted imaging (DWI): pus shows restricted diffusion (bright on DWI, dark on the ADC map). This helps separate an abscess from a necrotic glioma or metastasis, which also ring-enhance.
- Blood cultures, echocardiogram, chest film, and ENT and dental review to find the source.
- Pus from aspiration gives the organism.
No lumbar puncture in a brain abscess or empyema. It rarely helps and can cause herniation.
Ring-enhancing lesions: "MAGIC DR": Metastasis, Abscess, Glioblastoma, Infarct (subacute), Contusion, Demyelination, Radiation necrosis. (Add tuberculoma, toxoplasmosis and cysticercosis in our setting.)
Management
- Early surgical drainage is the mainstay: burr-hole or image-guided aspiration (repeated if needed), or excision for multiloculated, thick-walled, fungal or post-traumatic abscesses with foreign material.
- IV antibiotics: broad spectrum first (commonly a third-generation cephalosporin plus metronidazole for anaerobes; add anti-staphylococcal cover after trauma or surgery), then guided by culture. Continue for at least 6 weeks; switch to oral only on microbiology advice.
- Treat the source: sinus or mastoid surgery, dental extraction.
- Anticonvulsants: up to half of patients have seizures at some point, so consider prophylaxis.
- Steroids only for dangerous oedema (they reduce antibiotic penetration and capsule formation).
- Follow with serial scans.
Mortality is low with early drainage (around 4% in Bailey & Love), but rises to over 80% if the abscess ruptures into the ventricles (ventriculitis). Some series report higher overall mortality, so prompt diagnosis matters.
Subdural empyema
- Pus in the subdural space, usually from frontal sinusitis, mastoiditis or meningitis, or after trauma or surgery.
- Pus spreads over the convexity and along the falx, causing cortical vein thrombosis, seizures and deficits; mortality about 8–12%.
- Pott's puffy tumour = frontal bone osteomyelitis with a doughy scalp swelling over the forehead, often with an empyema beneath.
- CT: a crescent of low or similar density with an enhancing rim, plus swelling and midline shift; can be missed on non-contrast CT (MRI is better).
- No LP. Treat with craniotomy (or craniectomy) and drainage, plus antibiotics; burr holes in selected cases.
Neurocysticercosis and other parasitic lesions
- Caused by larvae of the pork tapeworm (Taenia solium); common in South Asia.
- Commonest presentation: seizures. Imaging shows small cysts, some with a scolex ("dot in a cyst"), ring-enhancing lesions or calcified dots.
- Treatment: anticonvulsants; albendazole with steroid cover for viable cysts; surgery (or endoscopy) for intraventricular cysts causing obstructive hydrocephalus.
- Hydatid cysts may also occur in the brain; they must be removed whole without rupture.
Surgical site infection in neurosurgery
Size of the problem
- Cranial surgery is clean surgery, yet craniotomy wound infection occurs in around 5% of cases.
- Infections may be superficial (skin), deep (bone flap osteomyelitis, extradural abscess) or organ space (meningitis, ventriculitis, abscess, empyema).
- Shunt infection: mostly within 1 month of insertion; mainly coagulase-negative staphylococci (Staph. epidermidis) that form a biofilm on the plastic, plus Staph. aureus.
Risk factors
Long operations, re-operation, CSF leak, external drains left in for long periods, implants (shunts, plates), very young or old patients, open myelomeningocele, diabetes, steroids, and staff traffic through theatre.
Prevention
- Prophylactic antibiotic at induction (single dose, repeated for long cases).
- Careful skin preparation; avoid shaving with a razor; minimal handling of implants; watertight dural closure; careful drain care and closed drainage systems; shortest possible EVD duration.
- Prion precautions: when a patient is at risk of Creutzfeldt-Jakob disease (family history, pituitary-derived growth hormone, cadaveric dural grafts, earlier neurosurgery), instruments are quarantined or destroyed, because routine sterilisation does not destroy prions.
Recognition and management
| Infection | Features | Management |
|---|---|---|
| Superficial wound | Redness, discharge, wound breakdown | Swab, antibiotics, wound care |
| Bone flap infection | Discharging sinus, persistent wound breakdown, swelling | Remove the bone flap, debride, antibiotics; replace with cranioplasty months later |
| Shunt/EVD infection or ventriculitis | Fever, wound redness, shunt failure, abdominal pain; cloudy CSF | Remove the device, external drainage, IV (± intraventricular) antibiotics, new shunt once CSF is clear |
| Post-operative abscess or empyema | Deterioration, seizures, new deficit | Imaging, drainage, prolonged antibiotics |
Expect: organisms after head injury or neurosurgery, meningitis with CSF leaks from basal skull fractures, CT before LP, CSF patterns for bacterial, viral and TB meningitis (TB: lymphocytes, high protein, low glucose), brain abscess sources (sinus, ear, dental, endocarditis, cyanotic heart disease), ring enhancement on contrast CT and restricted diffusion on DWI, drainage plus at least 6 weeks of antibiotics, LP contraindicated, ventricular rupture raising mortality, subdural empyema and Pott's puffy tumour, neurocysticercosis causing seizures, and shunt infection with coagulase-negative staphylococci treated by removing the shunt.
Quick revision
- CSF leak + basal fracture → meningitis risk (about 25%).
- CT before LP if focal signs, papilloedema, low GCS, seizures, recent surgery.
- Bacterial CSF: polymorphs, high protein, low glucose. TB: lymphocytes, high protein, low glucose. Viral: lymphocytes, normal glucose.
- Brain abscess: mass features, mild fever, ring-enhancing, DWI bright, no LP.
- Drain early; antibiotics at least 6 weeks; consider anticonvulsants.
- Subdural empyema: sinusitis, crescent with enhancing rim, craniotomy.
- Neurocysticercosis: seizures; albendazole with steroids; surgery for ventricular cysts.
- Infected shunt or bone flap: remove it, treat, reconstruct later.
Written by The House Job from standard surgical references (Bailey & Love; Kumar and Clark's Clinical Medicine).
FAQ
How can a brain abscess be told apart from a tumour on imaging?
Both can ring-enhance, but an abscess usually has a smooth thin wall and shows restricted diffusion (bright) on diffusion-weighted MRI, while most necrotic tumours do not.
How long are antibiotics given for a brain abscess?
At least 6 weeks, intravenous at first, together with surgical drainage.
Why does a patient with a skull base fracture get meningitis?
A dural tear lets CSF leak into the nose or ear and lets nasal bacteria such as pneumococcus reach the subarachnoid space.
What is Pott's puffy tumour?
Osteomyelitis of the frontal bone, usually from frontal sinusitis, giving a soft swelling of the forehead, often with an underlying subdural or extradural empyema.
Why must an infected shunt usually be removed?
Bacteria such as Staph. epidermidis form a biofilm on the tubing that antibiotics cannot clear, so cure needs removal and later reinsertion.