Sub-Arachnoid Hemorrhage (SAH)

Introduction

A subarachnoid cerebral hemorrhage (SAH) is a bleeding in the brain where blood leaks into the space between the brain and the meninges (the protective layers surrounding the brain). This space is known as the subarachnoid space. This space, approximately one centimeter thick, is located between the pia mater and the arachnoid membrane. Within this space are vital blood vessels that supply and drain the brain. An SAH therefore occurs in the area where important blood vessels meet.

A SAH is often accompanied by a very sudden, severe headache that comes on out of nowhere. The intensity of this headache is often the worst headache anyone has ever experienced.
It is sometimes described as a "thunderbolt" headache. Patients often experience nausea with or without vomiting. The headache can radiate to the neck and shoulders.
Yet, 12 to 51 % of patients with a subarachnoid hemorrhage are initially misdiagnosed as a migraine or tension headache.

Symptoms

• Sudden onset
• Maximum pain (97% of cases) within seconds or minutes of onset
• Often severe ("worst headache of life")
• Usually nausea or vomiting
• In rare cases, there is no headache, but only neck pain or sudden confusion, for example

A SAH is a relatively uncommon brain hemorrhage. Approximately 3-5% of all strokes are SAHs. About half of SAH cases occur in people under 55. Therefore, a relatively young group of people is often affected.

Every brain hemorrhage has a huge impact, but when a family with young children and work life are also turned upside down, the consequences are even more severe.

What makes an SAH particularly concerning is that a vulnerable period begins in the two weeks following the SAH. In some cases, new symptoms occur as a result of a new stroke. To closely monitor these and other potential consequences, people with an SAH must stay in the hospital for approximately two weeks.

Causes

Brain Aneurysm
The cause of a SAH is often the rupture of a brain aneurysm.

An aneurysm is a dilation of the blood vessels (sometimes a balloon-like shape) that, over time, develops into a weakness in the blood vessel. In some people, aneurysms develop in the brain in a major blood vessel network at the base of the brain. This network, the Circle of Willis, acts like a roundabout for blood flow.

An aneurysm often ruptures when there's a sudden, large increase in blood pressure, for example, due to physical activity, but it can also rupture "out of the blue." Whether you develop an aneurysm is often a matter of bad luck. Smoking, alcohol, and drug use are risk factors for developing an aneurysm. Genetics also play a role. Women have a higher risk of developing an aneurysm than men.

Perimesencephalic Hemorrhage
Perimesencephalic hemorrhage literally means: bleeding around the midbrain (mesencephalon). The mesencephalon is a part of the brainstem. The blood from the hemorrhage accumulates in the midbrain cisterns.
Cisterns are extensions of the subarachnoid space through which cerebrospinal fluid circulates. A perimesencephalic hemorrhage is a subarachnoid hemorrhage (SAH) that is not caused by an aneurysm. Approximately 10%-15% of SAH bleeds are perimesencephalic hemorrhages.

Physical impairment is often minimal or completely absent. Loss of consciousness or decreased level of consciousness is rare.
Complications, such as hydrocephalus, reduced cerebral ischemia, and new hemorrhages, are rare.
The prognosis is generally better than a SAH after an aneurysm, in terms of survival rate and clinical course (how quickly someone can recover during hospitalization).

However, the invisible consequences of this type of brain injury are often underestimated. There are often many consequences, such as fatigue, (disrupted) stimulus processing, or cognitive impairment.

According to researchers, a third of people with a perimecencephalic hemorrhage still experience symptoms after five years. See, for example, this study and the study linked here. It is therefore recommended that this group of patients also receive long-term follow-up after discharge from the hospital.

No known cause
In some patients, no underlying cause is found. This is called an angiographically negative SAH. Sometimes the blood is mainly visible around the brainstem (perimesencephalic SAH), in which case it is suspected to originate from a small venous or capillary blood vessel.

In other cases, the bleeding pattern is more diffuse, but still without demonstrable vascular abnormality. Possible explanations include a small vein hemorrhage, a clotting disorder, vasculitis, a dissection (tear in the blood vessel wall), a rare connective tissue disease, or a dural fistula.
A dural arteriovenous fistula (DAVF) is a direct connection between an artery and a vein in the dura mater. This causes increased pressure in the vein that carries the blood.

A tangle of blood vessels, also called an arteriovenous malformation (AVM), may be another, but rare, cause. An AVM, like an aneurysm, is a weak spot in the vascular system, which may cause bleeding.

The breakdown of the causes of SAH in figures