Description

An infant presented with progressive encephalopathy, poor feeding, low-grade fever and intermittent seizures for the past month. He was normal at birth and received age-appropriate vaccination. He had focal-onset, right-sided, tonic motor seizures. He developed intermittent, generalised, dystonic posturing of the body for the past week. Family history was not contributory. On examination, he was lethargic with bouts of irritability, had intermittent generalised dystonia with bizarre postures and was poorly responsive to parents and surroundings. He had a bulging anterior fontanelle, increased tone and brisk deep tendon reflexes. BCG scar was absent. There was no organomegaly or lymphadenopathy. A provisional diagnosis of subacute febrile encephalopathy with raised intracranial pressure and dystonia, secondary to tubercular or complicated bacterial meningitis, was considered.

Cerebrospinal fluid (CSF) examination showed lymphocytic pleocytosis (total cell count 79, 80% lymphocytes), hypoglycorrhachia (glucose 12 mg/dL), raised protein (656 mg/dL), absence of organism on Gram stain and bacterial culture and a positive gene-Xpert assay (cartridge-based nucleic acid amplification test). Contrast-enhanced CT (CE-CT) scan of the brain showed non-communicative hydrocephalus, periventricular interstitial oedema, leptomeningeal enhancement, bilateral basal ganglia infarcts and typical basal exudates in the basal cistern resembling ‘inverted starfish’ in appearance (inverted starfish sign, figure 1A). This typical radiological appearance confirmed the presumptive diagnosis of tubercular meningitis (TBM) with complications in the index patient. He underwent a ventriculoperitoneal shunt and was initiated on four-drug antitubercular therapy. He has shown good recovery with residual dystonia and spasticity.

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Figure 1

(A–F) Axial contrast-enhanced CT of five different patients with tubercular meningitis (A–E) showing enhancement of the basal meninges along the lamina terminalis cistern (black arrow), sylvian cisterns (white solid arrows) and crural cisterns (interrupted white arrows) representing the arms of the starfish and suprasellar cistern (star) representing the central ring canal of the starfish. (F) Diagrammatic representation of inverted starfish.

TBM is a devastating central nervous system infection, especially in infants and young children. The clinical presentation may mimic several other neurological illnesses and the duration of symptoms may not always be prolonged or subacute in onset as is typically known. Low-grade fever and early irritability are often missed; hence, infants may present with complications, including infarcts and hydrocephalus, as seen in the index child. TBM is a paucibacillary disease with poor sensitivity to Ziehl-Neelsen stain and culture, and in the absence of a reliable and rapid gold standard diagnostic test, the mycobacterial confirmation and initiation of treatment is often delayed. Our case highlights that a simple CE-CT scan can aid in the early diagnosis of TBM, especially in resource-constrained settings. The ‘inverse starfish sign’ seen in the basal sections corroborates the clinical diagnosis, especially while CSF confirmation is awaited or when CSF is contraindicated due to raised intracranial pressure. We have seen this sign consistently in several patients (figure 1B–F).

Rich and McCordick demonstrated the pathogenesis of TBM in an autopsy series.1 TB meningitis is not a direct infection of the meninges as seen in bacterial meningitis. Instead, a focus of infection is formed under the cortical pia and periventricular areas, aptly named as the Rich focus, after the physicians who described it.2 These foci caseate from time to time and the tubercle bacilli get shed in the subarachnoid space, causing granulomatous inflammation of the meninges. The immune response of the host to the bacilli, in the subarachnoid space, leads to the formation of thick inflammatory exudates containing erythrocytes, macrophages and lymphocytes, most marked in the interpeduncular fossa, but extends to involve the suprasellar region, prepontine cistern and spinal cord. The vessels in the circle of Willis may come in contact with these exudates, leading to a vasculitis reaction within them, thereby causing infarctions in their draining territories. In a CE-CT, this inflammatory cascade is seen as a zone of contrast enhancement, which gives rise to the typical sign being described here. The basal exudation is typically seen inup to one-third of TBM patients.3 In our experience, this pattern of contrast enhancement is characteristic of TBM and provides an easy bedside tool for neurologists to suspect TBM, especially in children.