Organised Chronic Subdural Hematoma Misinterpreted as Extradural Hematoma: A Rare Diagnostic Challenge

Abstract

Background: Organised chronic subdural haematoma (OCSDH) is an uncommon advanced form of chronic subdural haematoma characterised by thick encapsulating membranes and an organised clot. Its appearance on non-contrast computed tomography (NCCT) may mimic an extradural haematoma (EDH), creating diagnostic and intraoperative challenges. Case Presentation: A 74-year-old man presented with a 10-day history of headache and vertigo, without a history of recent trauma, vomiting, focal neurological deficits, or hypertension. Neurological examination was normal (Glasgow Coma Scale 15/15). NCCT revealed a 19-mm-thick, lentiform, isodense right frontoparietal extra-axial collection with a 5-mm midline shift, initially interpreted as an acute-to-subacute EDH. Emergency decompressive craniotomy was performed. No extradural clot was found; the dura was intact and tense. Careful dural opening revealed a thick, vascular outer membrane enclosing an organised clot with partially liquefied haematoma, confirming OCSDH. The outer membrane was excised, and the haematoma was evacuated. A thin, translucent inner membrane adherent to the arachnoid was preserved to minimise cortical injury and bleeding. Postoperative NCCT on days 1 and 7 demonstrated complete haematoma evacuation, resolution of the midline shift, and satisfactory brain re-expansion. The patient recovered without new neurological deficits. Conclusion: OCSDH can closely mimic EDH on NCCT, particularly when a lentiform extra-axial collection is present. Discordance between imaging findings and intraoperative anatomy should prompt careful reassessment and dural exploration. Selective outer membranectomy with haematoma evacuation can achieve satisfactory decompression while avoiding injury associated with aggressive inner membrane stripping. Contrast-enhanced CT or MRI may aid diagnosis in equivocal cases when clinically feasible.