Nonaneurysmal perimesencephalic subarachnoid haemorrhage

A 52-year-old male with a history of new-onset headache. No neurologic deficits were noted and vital signs were stable on admission. No history of trauma and anticoagulation.

The patient initially underwent a plain computed tomography without contrast which revealed a subarachnoid haemorrhage in the perimesencephalic cistern with extension to the right ambient cistern. (Figure A). No blood was seen in the bilateral Sylvian fissures and there was no intraventricular haemorrhage (Figure B). Digital subtraction angiography did not show vascular malformations that justified bleeding (Figure C).

Control CT of the brain without contrast 48 hours after bleeding showed a decrease in perimesencephalic haemorrhage. (Figure D).

Nonaneurysmal perimesencephalic subarachnoid haemorrhage (NAPHs) is characterized by accumulation of subarachnoid blood predominantly around the midbrain and absence of an aneurysm or other source of bleeding on angiography. Clinical and radiological characteristics suggest a venous origin of PMH. It represents approximately 10% of all episodes of spontaneous subarachnoid haemorrhage (SAH) [1].

Clinical presentation

The clinical presentation of patients with NAPHs is similar to that of patients with aneurysmal SAH, with a history of unusually severe headaches of sudden onset. It is often associated with photophobia and meningism.

It presents a benign clinical course and evolution, with no risk of vasospasm or rebleeding in the first years after the haemorrhage and with a normal life expectancy.

Key diagnostic features:

NAPHs are characterized by the absence of an aneurysm or other source of bleeding on 4-vessel digital subtraction angiography [1] and subarachnoid blood located predominantly in the perimesencephalic cistern. May extend into the basal and suprasellar cisterns, into the medial Sylvian fissure and interhemispheric fissure.

May settle as sediment in the occipital horns of the lateral ventricles but there is no overt intraventricular hemorrhage. [2]

NAPH is associated, in some cases, with the presence of a primitive variant pattern of drainage from the basal vein of Rosenthal (BVR) with direct connection of the perimesencephalic veins into the dural sinuses in at least one hemisphere. [4]

Differential diagnosis

Subarachnoid haemorrhage (SAH) is a type of extra-axial intracranial haemorrhage and denotes the presence of blood within the subarachnoid space. Trauma is the most common cause of SAH, and saccular aneurysm rupture is the most common cause of nontraumatic SAH that diffusely fills the suprasellar and central basal cisterns and extends peripherally to the cerebral convexities.

Pseudo Subarachnoid haemorrhage, it is usually due to cerebral oedema. This is seen in hypoxic-ischemic brain injury and recent resuscitation from cardiopulmonary arrest. Often seen in CT with generalized cerebral oedema or basal cistern effacement.

Cortical laminar necrosis is necrosis of neurons in the cortex of the brain in situations when the supply of oxygen and glucose is inadequate to meet regional demands. This is often encountered in cardiac arrest, global hypoxia and hypoglycemia. On MRI, cortical lamellar necrosis is characterized by areas of high signal on T1W images located in the cortex, which gives it its characteristic linear appearance. In most cases, only a subtle high cortical density seen on CT, with cisterns free of bleeding.

Treatment

CT Angiography is recommended to investigate for possible aneurysm cause. Symptomatic treatment.

Teaching Points

Blood is centered immediately anterior to the midbrain or pons and may variably involve the interpeduncular, crural, ambient, quadrigeminal, prepontine, or carotid cisterns

Blood may extend into the suprasellar cistern and the basal portions of the sylvian and interhemispheric fissures.

Small amounts of blood may sediment in the occipital horns of the lateral ventricles, but there is no frank intraventricular haemorrhage. [3]