Acute non-traumatic subdural hematoma induced by intracranial aneurysm rupture

Abstract Rationale: Intracranial aneurysm with the first manifestation of acute subdural hematoma (aSDH) is rare in the field of neurosurgery. Usually subarachnoid hemorrhage or intracranial hematoma happens after the rupture of an intracranial aneurysm, whereas trauma is the primary cause of aSDH. Patient concerns: Here, we present the case of a 71-year-old woman who presented with spontaneous aSDH with progressive headache and vomiting. Diagnosis: Urgent head computed tomography (CT) identified an aSHD, but the patient had no history of trauma. CT angiography (CTA) identified the cause of the aSDH as rupture of an intracranial aneurysm in the left middle cerebral artery. Interventions: Emergent craniotomy with hematoma evacuation was performed. Outcomes: Due to prompt diagnosis and appropriate intervention, the patient recovered fully with no disability. Lessons: This unique case demonstrates that aSDH caused by intracranial aneurysm rupture requires timely identification and appropriate action to prevent adverse outcomes. We performed a comprehensive systematic literature review to examine the etiology and pathogenesis of non-traumatic aSDH. Furthermore, digital subtraction angiography should be considered in patients diagnosed with an aSDH with no known cause.


Introduction
Although spontaneous acute subdural hematoma (aSDH) in the absence of trauma is a rare condition, [1] the associated mortality and morbidity rates are high. Non-traumatic aSDH is far less common that spontaneous aSDH occurring in the absence of an intracranial aneurysm. The etiology and pathogenesis remain uncertain given the infrequency of spontaneous non-traumatic aSDH. Arteriovenous fistulas, [2] rupture of an arachnoid cyst [3,4] or vasculature structure, hematological malignancies, [5] coagulation defects, [6][7][8] and cocaine abuse [9] have been reported to contribute to the occurrence of non-traumatic aSDH in specific cases. In particular, the rupture of an intracranial aneurysm may have severe consequences if misdiagnosed, with an associated mortality estimated to range from 60% to 76.5%. [10] Typical clinical manifestations are symptoms caused by intracranial hypertension, such as vomiting, headache, conscious disturbance, visual impairment, and brain hernia. Treatments include surgical decompression, hematoma evacuation, ventricular drainage, and conservative therapy.
In the report, we present a case of aSDH in a patient who presented with progressive headache and vomiting but no history of recent trauma. In consideration of the low incidence of the condition, the current literature was reviewed to elucidate the etiology and pathogenesis of non-traumatic aSDH as well as current standards for its diagnosis, treatment, and prognosis.

Case report
A 71-year-old woman presented to the out-patient department with progressive headache and vomiting without a recent history Editor: Maya Saranathan.
XG and FY have contributed equally to this work and should be considered cofirst authors.
of traumatic injury. The patient had no history of hypertension and medication use. She complained of a sudden headache occurring 2 weeks previously as well as occurring approximately 6 weeks previously. Two weeks prior to her presentation at our hospital, she visited a local hospital for computed tomography (CT) and magnetic resource imaging (MRI) examinations with no positive results (Fig. 1). Symptom-based treatments were given to her at that time. On examination in our hospital, CT showed the patient had aSDHs in the left temporal lobe with central line deviation (Fig. 2). The initial laboratory tests yielded no abnormal results. Given the unknown cause of non-traumatic aSDH, magnetic resonance angiography (MRA), and computed tomography angiography (CTA) were performed, and an intracranial aneurysm was found in the M1 distal bifurcation of the left middle cerebral artery (Fig. 3).
Emergent craniotomy with hematoma evacuation was performed in the left brain. The intracranial aneurysm in the left middle cerebral artery was clipped in the operation. Obvious adhesions were observed intraoperatively between the aneurysm and arachnoid membrane (Fig. 4). The patient experienced a full recovery (Fig. 2) and was discharged 2 weeks later with a Glasgow outcome scale of 5. The Ethics Committee of the First Hospital of Jilin University approved our study protocol, and the patient had provided informed consent for publication of the case. (NO. is 2019-296).

Discussion
A review of English reports of aSDH case caused by aneurysm was conducted by searching the PubMed databased between January 2013 and January 2018. The terms "aneurysm and acute pure subdural hematoma" were used to search for the publications. Eight publications were eventually included in our analysis ( Table 1). The method for identifying appropriate publications is described in Fig. 5. Cases were indexed by age, symptoms, location of aneurysm or aSDH, treatment, examina- tion, and outcome. Of the 8 cases, 3 were men and 5 were women. The age of patients ranged from 25 to 51 years. In 2 cases, the aSDH was located posterior to the communicating artery aneurysm. Three cases involved middle cerebral artery aneurysm, and 2 cases had an internal distal carotid artery aneurysm. Finally, 1 case had an aneurysm in the distal anterior cerebral artery. In these cases, headache was the most common initial symptom. However, coma, vomiting, and nausea also have been reported as presenting symptoms. Digital subtraction angiography (DSA) is the preferred diagnostic modality for aneurysms. Most of the retrieved cases were diagnosed by DSA. Three cases with aneurysm were not diagnosed immediately. One was diagnosed by indocyanine green videoangiography during aneurysm surgery after a diagnosis could not be made based on MRA and CTA. Hematoma evacuation and aneurysm clipping were performed for the treatment of all patients in the included studies. Good recovery was reported for 6 patients, while a poor recovery with disability was experienced by 2 patients. No deaths occurred among the 8 reviewed cases. The non-traumatic causes of aSDH are listed in Table 2.
Few publications have addressed the prevalence of spontaneous non-traumatic aSDH, and spontaneous aSDH caused by aneurysm is quite rare. [1] Aneurysms commonly lead to subarachnoid hemorrhage, ventricular hemorrhage, or intracranial hematoma, while trauma is the primary cause for aSDH. [25] It is easy to overlook the existence of aneurysms in aSDH. Ohkuma et al [1] reported that the incidence of subarachnoid hemorrhage or ventricular hemorrhage caused by aneurysm is only 1.5% to 2.7%, whereas the incidence of spontaneous aSDH caused by aneurysm was even lower due to the invisibility. With an aSDH, blood usually accumulates in the surface of dura mater and cerebral cortex, which may result in severe consequences due to compression. [10] The cause of aSDH in the case reported here was confirmed to be aneurysm rupture. The pathogenesis of aSDH caused by aneurysm rupture remains unclear for now, but there are a few possible hypotheses. It was suggested that the high blood pressure created during aneurysm rupture may lead to aSDH as a result of damage to the arachnoid. Alternatively, the aSDH could be caused by the rupture of an aneurysm located in the subdural space. [26] Ultimately, the normal structure of the arachnoid had been destroyed by a previous microvascular aneurysm hemorrhage, allowing the broken tissue from the aneurysm to penetrate the subdural space when a second rupture of the aneurysm occurred, which may likely be the pathogenesis of the aSDH in this case. The patient complained of a sudden headache twice in approximately 6 weeks. Although it was not seen on CT and MRI examinations, there is a high possibility that a microvascular aneurysm hemorrhage existed. [27] Arachnoid adhesion and damage may also exist in this situation secondary to microvascular aneurysm hemorrhage, which was confirmed during the surgery. However, the second hypothesis cannot be completely ruled out, and the occurrence of aSDH in this case may have been influenced by a variety of interacting factors.
The definition of aSDH caused by aneurysm remains controversial. Spontaneous aSDH was suggested to represent aSDH caused by aneurysm, while a contrary opinion stated that spontaneous aSDH should be referred to as aSDH caused by spontaneous rupture of vasculature. Neutrally, spontaneous aSDH may include all forms of aSDH caused by non-traumatic reasons. [2][3][4][5][6][7][8][9]19,21,22,23,28,29] There is a risk of missed diagnosis for aSDH caused by aneurysm. DSA has been considered the golden standard for diagnosing aneurysm, as it is capable of tracking the location of an aneurysm and identifying the relationship between the aneurysm and nearby artery. However, there is a risk of radiocontrast agent leakage during DSA procedures. Compared with DSA, CTA has the advantage of a shorter diagnostic time frame, which is especially beneficial for critically ill patients. [30] Treatments options for aSDH include surgical decompression, hematoma evacuation, ventricular drainage, and conservative therapy. Conservative therapy is reasonable for minor defects. Ventricular drainage can be used in the absence of coagulation defects. However, surgical decompression and hematoma evacuation are advised to prevent adverse outcomes such as motor or sensory deficits.
Although a rare cause of aSDH, aneurysm should be considered in efforts to diagnose the cause of non-traumatic       Table 2 Acute subdural hematomas caused by non-traumatic reasons.