Neural Med Chir (Tokyo) 39, 33 -- 35, 1999 Abrupt Exacerbation Mimicking of Acute Subdural Benign Acute on Computed -Case Epidural Hematoma Hematoma Tomography Report- Kunihiko KATO,Osamu WATANABE, and Yoshinori OZAWA Departmentof Neurosurgery, ChibaRosaiHospital,Ichihara,Chiba Abstract A 75-year-old malewashitbya car,whenridinga bicycle.Thediagnosisofacuteepiduralhematoma wasmadebasedon computedtomography (CT)findingsof lentiformhematoma in thelefttemporal region.Onadmission he hadonlymoderateoccipitalgia andamnesiaoftheaccident,so conservative therapywasadministered. Thirty-three hourslater,he suddenly developed severeheadache, vomiting, andanisocoriajustaftera positionalchange.CTrevealedtypicalacutesubduralhematoma (ASDH), whichwasconfirmedbyemergent decompressive craniectomy. Hewasvegetative postoperatively and diedof pneumoniaonemonthlater.Emergentsurgicalexploration is recommended forthistypeof ASDHevenif thesymptoms are milddueto agedatrophicbrain. Keywords: acutesubduralhematoma,lentiform hematoma,acuteepidural hematoma, abruptexacerbation, computed tomography ambulance. He had total amnesia about the accident. He had signs of blows on the left side of the body but could talk and walk normally. CT one hour after the accident revealed an intracranial clot, which prompted emergency transfer to our hospital. On admission, he had only moderate occipitalgia and amnesia about the accident. The initial CT at the Introduction Acute epidural hematoma (AEDH) generally ap- pears on computed tomography (CT) as a lentiform and homogeneous high density lesion with or without associated lesions of the overlying skull and soft tissues.',",") In contrast, acute subdural hematoma (ASDH) has a crescent shape, often accom- previous clinic showed a lentiform, homogeneous hematoma, 2 cm in thickness, in the left temporal extracerebral region. Additionally, his atrophic brain had an old infarction in the corona radiata panied by cerebral contusion.",") The clinical presentations are also quite different, as patients with AEDH may appear totally alert during the lucid interval, whereas patients with ASDH are usually comatose because of severe parenchymal brain damage. We describe a case of atypical lentiform ASDH in an aged person with atrophic brain, in whom the symptoms exacerbated abruptly after 33 hours of lucid interval. A 75-year-old male was the victim of a hit and run accident, when riding a bicycle. He was found lying in the road, and was taken to the nearest clinic by (Fig. 1). Laboratory studies including the coagulation function showed no remarkable abnormality. The tentative diagnosis of AEDH was based on the CT findings and clinical features. Conservative therapy was selected considering his mild symptoms and age. Repeat CT at 7 hours and 24 hours after the accident showed no remarkable change. However, careful observation of the hematoma disclosed a low density area with a niveau (Fig. 2). Conservative therapy was continued. Thirty-three hours after the accident, he suddenly Received April Author's present Clinic, Case 1, 1998; address: Report Accepted September 3, 1998 K. Kato, M.D., Chiba Neurosurgical 33 Chiba, Japan. 34 K. Kato et al. complained of severe headache and vomited just after sitting up to get into a wheelchair. Neurological examination revealed dilatation of the left pupil. Immediate CT showed a typical ASDH (Fig. 3) which was confirmed by emergent decompressive craniectomy and hematoma evacuation. Multiple bleeding points from the cortical artery and bridging vein were seen but no AEDH. Expansion of the brain was poor even after hematoma removal. He did not recover well postoperatively and died of pneumonia one month later. Fig. 1 Fig. 2 Fig. 3 Initial computed tomography scans 1 hour after the accident revealing a lentiform, homogeneous hematoma in the left temporal extracerebral region. Note the atrophic brain with old infarction in the corona radiata (arrow). Computed tomography scans 24 hours after the accident showing no remarkable change. Note the low density area above the hematoma with a niveau (arrow). Emergent computed tomography hours after the accident showing acute ation. subdural hematoma with scans 33 a typical brain herni- Discussion ASDH is generally considered to appear as a crescentic high density area on CT. However, CT has revealed many atypical hematoma types, 814% of ASDH appeared as the lentiform shape. 1,5,11) The appearance of ASDH on CT can be classified into three types: concave (crescent), straight, and convex (lentiform).5) About 13% of high density subdural hematomas (including rebleeding in chronic subdural hematoma) had convex margins. CT shows some differences between lentiform ASDH and AEDH: The round inner border of lentiform ASDH is hyperconvex and forms an angle of almost 90 degrees with the skull, and it is heterogeneous.1) The low density area of it is superiorly separated by a niveau from an inferior hyperdense area, possibly due to an influx of the cerebrospinal fluid through tears in the arachnoid membrane . This special heterogeneity, called the "sedimentation effect, "6) maybe related to the coagulopathy .') Another difference is that the margin of lentiform ASDH increasingly regains its characteristic crescentic shape at the periphery. However , only the characteristic of the heterogeneity was seen in our case . Coronal magnetic resonance (MR) imaging might be helpful in such a case to clarify the relationship between the hematoma, subarachnoid space , bridging veins, etc. The cause of the lentiform appearance of ASDH is unclear, but may have resulted from blockage of the subdural space by adhesions.1) Acute cerebral swelling may have prevented expansion of the hematoma , which became lentiform as a result . However, acute cerebral swelling did not occur till 33 hours after the accident in our case . Another problem in this case was the cause of the abrupt exacerbation 33 hours after the accident . Second impact syndrome 2.8)might have influenced this catastrophic change . Second impact syndrome is defined as diffuse cerebral swelling after repeated concussive brain injury received in sports .7) The pathology is thought to involve loss of autoregulaNeurol Med Chir (Tokyo) 39 , January, 1999 Abrupt Exacerbation of ASDH Mimicking AEDH on CT tion of the brain blood supply,') which leads to vascular engorgement, which markedly increases intracranial pressure. Additionally, the shift of the hematoma by a positional change and/or damage to the arterial twig, which is responsible for acute spontaneous subdural hematoma, 7,10,12,13) may have been involved in the exacerbation. Special attention must be given when CT shows lentiform hematoma adjoining aged atrophic brain. If ASDH is confirmed by differential diagnosis using CT and MR imaging, emergent surgery is recommended even if the patient is in good condition. References 1) Braun J, Borovich B, Guilburd JN, Zaaroor M, Feinsod M, Grushkiewicz I: Acute subdural hematoma mimicking epidural hematoma on CT. 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AJR Am J Roentgenol 131: 27-34, 1978 Address reprint requests to: K. Kato, M.D., Chiba Neurosurgical Clinic, 408 Naganumahara-cho, Inageku, Chiba 263-0001, Japan.