The exact location of a hematoma in relation to the pachymeninges contributes to typical radiographic presentations. However, because of the complexity of hematoma evolution and neomembrane formation, an unexpected intraoperative finding may lead to a change of surgical strategy. Besides, the concentration of hemoglobin and its degradation products, the integrity of red blood cells (RBCs), and the infiltration of fibroblasts, polymorphonuclear neutrophils, and macrophages are factors that affect the imaging characteristics on computed tomography (CT) and magnetic resonance imaging (MRI) as the hematoma ages. CASE DESCRIPTION:

An interdural hematoma (IDH), a hemorrhage that splits the periosteal dura mater from the meningeal dura mater, is an extremely rare occurrence and the diagnosis requires confirmation by surgical or pathological findings. By presenting a case of an IDH that had been misdiagnosed as a chronic subdural hematoma (CSDH) before surgery, and reviewing the literature, we propose the radiological characteristics of presenting both dural border sign and dural beak sign on MRI as a specific indicator for suspecting IDH preoperatively. CONCLUSIONS:

A careful evaluation of cerebral expansion before membranectomy was mandatory intraoperatively. For IDH, wide inner membranectomy (i.e. excision of meningeal dura mater) should not be necessary. An IDH should be considered as a distinct disease category while evaluating an extra-axial hematoma despite its rarity, since the characters of radiological, histopathological findings are different and surgical strategy varies from epidural or subdural hematoma in different hematoma stages ¹⁾.