Brain abscess and intracranial suppuration — formative SAQs

SAQ 1 (10 marks)

A nine-year-old boy presents to the emergency department with a one-week history of worsening frontal headache and low-grade fever, initially treated as sinusitis by his general practitioner. This morning his mother found him confused, unable to name his sister, and dragging his right leg. He is febrile at 38.6 °C, drowsy but rousable, with a right homonymous hemianopia and mild right-sided weakness. He has a history of chronic frontal sinusitis. A contrast CT shows a 2.8 cm ring-enhancing lesion in the left frontal lobe with surrounding oedema and midline shift. ^{[1] [2]}

1. Give your immediate resuscitation and imaging actions, and explain why you would not perform a lumbar puncture at this stage. (4) ^[1]
2. Describe the microbiological strategy you would use to identify the organism, and the empiric intravenous antibiotic regimen you would start. (3) ^[2]
3. Outline the neurosurgical options and the factors that determine whether this abscess is aspirated, excised or managed medically, and name the likely organisms given the sinus source. (3) ^{[1] [6]}

Model answer — SAQ 1

(1) Resuscitation and imaging (4). Resuscitate the brain first with ABCDE: secure airway, breathing and circulation; treat any seizure with a benzodiazepine escalating as needed; maintain normoglycaemia and normothermia. Because he has signs of raised intracranial pressure (drowsiness, hemianopia, weakness) with midline shift on CT, elevate the head of the bed to 30 degrees and give an osmotic agent — mannitol 0.25–0.5 g/kg IV or hypertonic (3%) saline 2–5 mL/kg IV — for impending herniation. Obtain a contrast MRI with gadolinium and diffusion-weighted imaging to characterise and date the lesion and confirm restriction of diffusion (supporting abscess over tumour). Refer urgently to paediatric neurosurgery and infectious diseases. A lumbar puncture is contraindicated because a space-occupying lesion is confirmed: it risks cerebellar herniation and adds no useful diagnostic information when pus can be obtained directly. ^[1]

(2) Microbiology and empiric antibiotics (3). Take blood cultures (two sets) before antibiotics if feasible, then obtain pus at aspiration or surgery — the cornerstone — sending it for Gram stain, aerobic and anaerobic culture, and 16S ribosomal RNA PCR for fastidious organisms. The yield is highest before antibiotics are given, which is why aspirating first (when safe) is so valuable. Start empiric intravenous therapy with a third-generation cephalosporin (cefotaxime or ceftriaxone) plus metronidazole to cover the streptococci (including the Streptococcus anginosus group) and anaerobes typical of a sinus source, then tailor once the organism and sensitivities are known. ^[2]

(3) Neurosurgical decision and organisms (3). Aspiration via a burr-hole or stereotactic route is the usual first approach: it is diagnostic, drains the collection, provides culture material, and can be repeated. Surgical excision is reserved for large, superficial, multiloculated or re-expanding lesions. Medical management alone is considered only for small (under about 2.5 cm), deep, or multiple lesions when the organism is known and the child is improving — not applicable here given the size and the midline shift. Given the frontal sinus source, the likely organisms are microaerophilic and anaerobic streptococci (the Streptococcus anginosus group), anaerobes such as Bacteroides, Prevotella and Fusobacterium, and sometimes staphylococci; polymicrobial growth is common. ^{[1] [6]}