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]

SAQ 2 (10 marks)

A four-year-old girl with unrepaired tetralogy of Fallot is brought in with a two-day history of headache, vomiting and a left-sided weakness that has progressed over hours. She is febrile, irritable, and has a GCS of 12, a new left hemiparesis, and a loud systolic murmur. Contrast MRI shows three ring-enhancing lesions at the grey–white junction, two on the right and one on the left hemisphere. [5] [2]

1. Explain the pathophysiological link between her cardiac lesion and the distribution of the abscesses, and state why haematogenous abscesses are often multiple. (3) [5]
2. Describe how her management differs from the single-lesion sinusogenic case in SAQ 1, including the role of cardiology. (4) [2]
3. Address the role of corticosteroids in her management, citing the evidence and the consensus position. (3) [4]

Model answer — SAQ 2

(1) Pathophysiology and multiplicity (3). Tetralogy of Fallot produces a right-to-left shunt that allows venous bacteria to bypass the pulmonary capillary filter and reach the systemic arterial circulation, seeding the brain. Bacteria lodge in poorly perfused areas at the grey–white junction, where the capillary bed is sparse, and the territory of the middle cerebral artery is most often affected. Because the seeding is haematogenous and distributed, multiple abscesses form, and they may be bilateral — distinguishing the pattern from a single contiguous (sinus or ear) abscess. [5]

(2) Management differences and cardiology (4). Resuscitation and empiric antibiotics (third-generation cephalosporin plus metronidazole) are the same, but the source-control strategy differs: multiple small haematogenous abscesses are often managed medically with serial MRI when the organism is known or confidently predicted, with aspiration reserved for the largest or most strategically placed lesion for diagnostic and decompressive purposes. Involve paediatric cardiology early, because timely surgical or catheter repair of the residual shunt is essential to prevent recurrence once the infection is controlled; she also needs endocarditis exclusion if there is bacteraemia. The duration of intravenous therapy is typically four to six weeks (often six to eight), guided by the clinical course, markers and serial imaging, with transition to oral therapy only if she is afebrile, clinically improved, with falling markers, complete source control and a suitable oral agent. [2]

(3) Corticosteroids (3). Corticosteroids are not used routinely. A systematic review and meta-analysis found that dexamethasone use was associated with higher mortality in brain abscess, although confounding by severity limits causal inference. The consensus, reflected in the 2024 ESCMID guideline, is to reserve corticosteroids for significant mass effect or impending herniation, use the lowest effective dose, and taper as soon as the oedema settles — because routine use may dampen the inflammatory response and delay capsule formation. In this child, I would use a short, tapering course of dexamethasone only if her conscious state or the mass effect dictated it, and would not continue it beyond the acute period. [4]