A 47-year-old man presents to the emergency department with a headache. He suddenly developed a throbbing, bitemporal headache about 5 hours ago "out of nowhere." He has a history of migraine headaches, but he feels that this headache is significantly more painful than his typical migraines. The patient took his prescribed sumatriptan with no relief of his symptoms. He also endorses nausea and he reports that he vomited once before arrival in the emergency department. The patient denies any recent trauma to the head. His medical history is significant for migraines and hypertension. He has a 20-pack-year smoking history and a history of cocaine use. He drinks 5-6 beers per week. His temperature is 98.6°F (37°C), blood pressure is 147/91 mmHg, pulse is 62/min, and respirations are 12/min. On physical exam, he appears to be in moderate distress and has pain with neck flexion. He has no focal neurologic deficits. A head CT is performed and can be seen in Figure A. This patient’s condition affects the space in between which of the following brain layers?
Periosteum and galea aponeurosis
Arachnoid mater and pia mater
Dura mater and arachnoid mater
Skull and dura mater
Arachnoid mater and pia mater
This patient presents with a sudden, severe headache and a head CT showing bleeding in the subarachnoid space, which confirms a diagnosis of subarachnoid hemorrhage. The bleeding in a subarachnoid hemorrhage occurs between the arachnoid and pia mater.

Subarachnoid hemorrhages present with a sudden, severe headache referred to as a “thunderclap” headache. Patients typically complain that the headache is the "worst headache of their life." Some patients also present with symptoms of meningeal irritation such as nausea and vomiting, nuchal rigidity, or focal neurologic deficits. Although most cases of subarachnoid hemorrhage are secondary to trauma, patients with risk factors such as hypertension and cocaine use can have non-traumatic presentations. Patients with an expanding bleed or acute neurologic changes require surgical clipping or embolization of the bleeding vessels.

Macdonald and Schweizer review the evidence regarding the treatment of patients with subarachnoid hemorrhage. They discuss how survival rates have improved with early aneurysm repair, prescription of nimodipine, and advanced intensive care support. They recommend early diagnosis in order to improve outcomes in these patients.

Figure/Illustration A is an axial slice of a head CT showing hyperintensity in the basal cisterns (red circle). This finding is consistent with bleeding in the subarachnoid space.

Incorrect Answers:
Answer B: Bleeding between the dura and arachnoid mater describes a subdural hematoma. A subdural hematoma presents as a headache with progressive confusion. It appears as a crescent-shaped lesion on head CT. Patients with an expanding bleed will require surgical decompression to avoid herniation syndromes.

Answer C: Bleeding between the periosteum and galea aponeurosis describes a subgaleal hemorrhage. Subgaleal hemorrhages occur in newborns and are caused by vacuum-assisted deliveries. Treatment is usually supportive as the bleeding will resolve by itself. Some patients with severe bleeds may require transfusion due to excessive blood loss.

Answer D: Bleeding between the periosteum and skull describes a cephalohematoma. Cephalohematomas occur in newborns and are caused by rupture of the blood vessels crossing the periosteum. They are usually secondary to a prolonged second stage of labor. Treatment is supportive as the blood will resolve and be resorbed.

Answer E: Bleeding between the skull and dura mater describes an epidural hematoma. An epidural hematoma presents as a brief loss of consciousness followed by a lucid interval and then progressive confusion or somnolence. It appears as a biconvex lesion on head CT. Treatment is with urgent surgical decompression as patients will rapidly decompensate after the lucid interval.

Bullet Summary:
Subarachnoid hemorrhage classically presents as a thunderclap headache with a brief loss of consciousness and meningismus.