Snake Bite and Radiology

Case Report  – 58 y male with h/o snake bite 5 days back presents for CT brain with altered sensorium which shows Large well defined, regular, hypodense, wedge shaped lesion in left supratentorial cerebral hemisphere in  fronto-temporo-parietal region with isilateral MCA not visualized /mass effect on the ventricle/ midline shift 3.5mm right/transfalcine herniation with no significant bleed or intravntricular extension  - likely represents acute /recent nonhemorrhagic infarction in MCA distribution post venomous bite(post vasculitic etiology) with no subarachnoid or parenchymal bleeds. Similar subtle, wedge shaped hypodense lesion is also seen in right perinsular region – likely of similar etiology with rest of the brain unremarkable. Case Submitted by Dr MGK Murthy, Dr GA Prasad.

Discussion

-Local manifestations of snake bite are  soft-tissue swelling from edema, necrosis, and hemorrhage. Common long-term sequelae of envenomation is soft-tissue atrophy distal to the bite, particularly in the digits.

-Systemic  signs and symptoms after a venomous snake bite are due to anticoagulant/procoagulant activity or neurotoxicity. Cerebral hypoxia can occur due to hypotensive shock that may accompany some snake bite envenomations. Neuromuscular disorders with  damage of the peripheral nervous system can with blockage of synaptic transmission, at either presynaptic or postsynaptic levels.

Common neurological symptoms are ptosis , ophthalmoplegia, limb weakness , respiratory failure, palatal weakness  and neck muscle weakness.

Cerebrovascular complications are –

• -           ischaemic strokes in various arterial territories,
• -          haemorrhagic stroke including multiple lobar haemorrhages with or without ventricular extension,
• -           haemorrhages in subarachnoid and subdural spaces,
• -          cerebellar haemorrhage, epidural haematoma,
• -          optic neuritis,
• -           delayed cerebellar ataxia,
• -          disseminated encephalomyelitis,
• -          leucoencephalopathy involving the basal ganglia and thalami (deep nuclei) as well as the cortical rim is rare.

Ischaemic stroke are caused by hypercoagulability and endothelial damage, immune-mediated vasculitis and systemic hypotension leading to multiple cerebral infarctions in more than 60% of cases suffering from snake bite.

Intracranial haemorrhages are related to abnormalities in haemostatic factors ranging from decreased platelets to a severe consumption coagulopathy.

 Optic neuritis can be from direct toxic effects of venom / vasoconstriction of optic nerve vascular supply/ retinal or systemic haemorrhages and hypersensitivity reaction to antivenom.

Delayed cerebellar ataxia or disseminated encephalomyelitis is mostly related to an immune-mediated damage triggered by antivenin administration.

Twenty minutes whole blood clotting test is an important simple measure for identification of a vasculotoxic snake bite.

Polyvalent ASV (anti snake venom), mannitol intravenous infusion, IV antibiotics & supportive care are prime modes of treatment.