Perimesencephalic subarachnoid hemorrhage (PSAH) is a specific type of bleeding that occurs in the subarachnoid space, the area surrounding the brain and spinal cord where cerebrospinal fluid circulates. Unlike other forms of subarachnoid hemorrhage, PSAH often has a more favorable outcome.
Understanding Perimesencephalic Subarachnoid Hemorrhage
Perimesencephalic subarachnoid hemorrhage refers to bleeding centered around the midbrain (mesencephalon) and into the basal cisterns. This bleeding is typically not caused by a ruptured aneurysm, which is a key difference from other subarachnoid hemorrhages. For this reason, it is often called “non-aneurysmal” PSAH.
The cause of non-aneurysmal PSAH is believed to originate from a venous bleed, rather than an arterial rupture. This contrasts with aneurysmal subarachnoid hemorrhage, where a weakened arterial wall ruptures. PSAH is rare, with an estimated incidence of about 0.5 cases per 100,000 adults each year. It accounts for 5% to 10% of all subarachnoid hemorrhages and around 33% of all non-aneurysmal cases.
The non-aneurysmal nature of PSAH contributes to its excellent prognosis. Unlike aneurysmal hemorrhages, PSAH has a lower risk of complications and rebleeding. The clinical course is benign, leading to better outcomes.
Recognizing the Signs
The most common symptom of PSAH is a sudden, severe headache, often described as a “thunderclap headache.” This headache reaches its maximum intensity within 60 seconds, and many describe it as the “worst headache of their life.” Other symptoms include nausea, vomiting, neck stiffness, and sensitivity to light.
Seek immediate medical attention if these symptoms occur. While PSAH has a good prognosis, it is crucial to rule out more severe conditions like aneurysmal subarachnoid hemorrhage. Prompt diagnosis ensures appropriate management and reassurance.
How It Is Diagnosed
Diagnosis of subarachnoid hemorrhage, including PSAH, begins with brain imaging. A computed tomography (CT) scan without contrast is the first step. This scan effectively detects blood in the subarachnoid space, especially within 24 hours of symptom onset.
If the CT scan is negative but bleeding is still suspected, a lumbar puncture (spinal tap) may be performed. This procedure collects cerebrospinal fluid from the lower back to check for blood or its breakdown products, confirming a hemorrhage when initial imaging is inconclusive.
After confirming subarachnoid hemorrhage, further imaging determines if an aneurysm is the cause. Cerebral angiography, often a CT angiogram (CTA), is recommended to rule out an underlying aneurysm. The diagnosis of perimesencephalic subarachnoid hemorrhage relies on excluding an aneurysm. Digital subtraction angiography (DSA) is considered a gold standard, though CTA is often an acceptable alternative.
Managing and Recovering
Treatment for perimesencephalic subarachnoid hemorrhage is primarily supportive, managing symptoms and promoting recovery. This includes pain management for severe headaches and a period of rest. Patients are closely monitored for potential complications, which are less common in PSAH compared to aneurysmal subarachnoid hemorrhage.
Complications like hydrocephalus (fluid buildup in the brain) or vasospasm (narrowing of blood vessels) can occur but are transient and less severe in PSAH. Hospital stays for PSAH are generally shorter than for aneurysmal subarachnoid hemorrhage, reflecting its benign nature.
Individuals diagnosed with PSAH have an excellent prognosis and normal life expectancy. Recurrence of bleeding is extremely rare. Most patients achieve functional independence upon hospital discharge and maintain favorable long-term outcomes. Follow-up care ensures complete recovery and addresses any lingering symptoms like mild headaches or fatigue.