Introduction
The incidence of Acute Epidural Hematoma(AEDH) is 1-2%1)among head injured patients.The AEDH iscommonlyde￾velopsunilaterally and caused resulting from coup mechanism with skull fracture in the vicinity of the impact site. We report an uncommon case of bilateral AEDH caused by coup and contrecoup mechanism.
 

Case report
A 25-year-old man was hit by a bike while riding a bicycle, and struck the right temporal region. He immediately became un￾conscious and was transported to our hospital. He had no specific past history.On admission, the Glasgow Coma Scale (GCS) was 13(E3V4M6) with bilateral pupil size of 3.5 mm in diameter.He complained of mild headache, but exhibited no neurological defi￾cits. His temporal region was significantly swollen and had bleed￾ing from the right external auditory canal suggesting skull base fracture. The computed tomography (CT) scan demonstrated trau￾matic symmetric thin bilateral AEDH (12ml of clot on the right￾and 13ml on the left side) atthe bilateral middle fossa and mild traumatic subarachnoid hemorrhage at the surface at the left tem￾poral lobe.The bone imaging CT revealeda linear fracture at the rightparieto-temporal bone tothe petrous bone. But, there was no fracture on the left side (Figure 1).

An emergencyevacuation of hematoma on the left side was then performed. During the operation, the bleeding point was the middle 
meningeal artery at the left middle fossa base, and successfully coagulated after hematoma evacuation (Figure 2).Postoperative course was uneventful and the righthematoma was conservatively treated. He was discharged at 30 days after injury without neurological defi￾cit.
 

Discussion
Traumatic AEDH is commonly caused by coup mechanism with a skull fracture unilaterally.AEDH concomitantly caused by coup and contra coup mechanisms are quite uncommon with an incidence of 0.5-10% in all AEDH[1-10]. In the cases of bilateral AEDH,unilateral hematoma often develops later without finding on the initial CT. The concomitantly developed AEDH caused by coup and / or cotra coup mechanisms is quite uncommon. Only eight cases have been reported in literature about AEDH caused by couand cotrecoupmechanisms[11-18].The clinical features of them are summarized in Table 1.

The six women and two men were mean aged of 48.4 years old (21 to 68).Many cases had skull fracture at the impact side, ex￾cept for Case 1, but the intracranial lesions and patient’s condition is quite various. Neurological states of the patient on admission were generally good[11-19].Patients with contrecoup mechanismAEDH had initial GCS of better than GCS 13 points except for Case 6. And, 4 cases (Case. 1, 2, 3, 5) underwent craniotomy(Table 1). The mechanism about the frontal AEDH caused by blow to the posterior region (Case. 1, 3, 4, 7, 8) has been comprehensively considered that the dura mat￾er of lateral frontal region is easily detached from the inner table of the skull, the skull is deformed and intracranial negative pres￾sure arise, small vessels of the superficial dura mater ormeningeal artery are injured by impact at the time of injury [13-16,18]. Kuwayama[20]has described the first case of spontaneous bilateral AEDH, but bilateral and concomitantly developed trau￾matic AEDH is quite uncommon.Although, in the present case, there was no skull base and convexity fracture on the left side and the bleeding vessel was the posterior middle meningeal artery. We guess that the negative pressure was caused, recovering the defor￾mation of skull due to deflection, as a result, detachment from the dura mater and injury of vascular occurred(Figure 3)

In the past report of pediatric AEDH without skull fracture[21]. In the children, the skull is easy deformed at the time of impact, so that detachment of dura matter. In our case, the curvature of parieto-temporal bone and mid￾dle cranial fossa may involve detachment of dura mater. The re￾view of the literatures[11-22] of bilateral epidural hematoma show the high incidence of young people (adolescence) and high energy accident. Whose have loose adhesion between the dural surface and the inner table of the skull and fibrous skull sutures with rela￾tively soft skull easily deform by the impact. These anatomical characteristics will be the risk of bilateral development of hema￾toma. The head-injured patient with some hemorrhagic tendency and/or hematological diseases has also the high risk of such hema￾toma development.Bleeding source of AEDH is commonly injury of artery, veins or sinus. On the other hand, previous report indicated that injury of small vessels from dura mater, which was detached from the inner table of the skull, causes AEDH. Only oozing from small dural vessels was recognized in four cases (Case. 1, 2, 3, 5), which underwent craniotomy. Our case was recognized injury of middle meningeal artery and active bleeding from it.There was no evidence on CT scan or subsequently at operation that a fracture was associated with AEDH. We considered that injury of middle meningeal artery was caused by detachment of dura mater in contre’ coup injury.The bilateral hematoma may develop simultaneously after the trauma and delayed development after evacuation of the he￾matoma. During the operation, the careful observation of the du￾ral tense after clot removal is mandatory if the patients have high risks. If the effect of decompression seems to be not enough with strong dural tense, an emergency Echo encephalogram or CT scan will necessary for the detection of theEnlargement of contralateral hematoma or newly developed hematoma.The delayed detection of the second hematoma is quite important to improve the final outcome of the patients.
 

Conclusion

We report that traumatic bilateral symmetric AEDHs, con￾trecoup epidural hematoma due to skull fracture and detachment 
of the dura mater from the base of the skull may be associated with rupture of the posterior middle cerebral artery causing a contral￾ateral epidural hematoma. This case demonstrates the importance of brain imaging after operation in cases of coup and contrecoup traumatic head injury.After the diagnosis of bilateral AEDH, immediate surgery is necessary. Unlike our case of asymmetric AEDH a simultaneous approach should be first considered since it promotes a quicker treatment and functional recovery even in patients under critical neurological conditions.

Figure 1: Initial skull Computed Tomography (CT) scan on admission showing a high density lesion at the bilateral parieto-temporal region, suggesting acute epidural hematoma (a, b), and traumatic subarachnoid hemorrhage at the left temporal tip (c). Skull CT scan with bone window demonstrating a fracture of parieto-temoral bone and petrous bone on the right side (d-f). 

His consciousness was gradually within 1.5 hours after injury.When the CT scan showing the growth of AEDH in the left con￾trecoup lesion (42ml), but no changed of the volume on the right side (Figure 2).

Figure 2: a.Initial Skull CT scan of the reconstruction 3D demonstrating afracture at the right parieto-temopral region andb. nofracture on the left side

Figure 3: Skull CT scan, taken one hour and half later, showing enlarge￾ment of the left hematoma.

Table 1: Clinical features of acute epidural hematoma caused by coup and cotrecoup mechanisms

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