Subpial hemorrhage is a rare form of extra-axial intracranial hemorrhage defined as hemorrhage between the cortical surface and the pia mater. It is an entity that is generally difficult to distinguish from subarachnoid hemorrhage.
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Epidemiology
Subpial hemorrhage has been typically described in neonates and infants, however, has also been reported in the adult population 1-3.
Clinical presentation
Subpial hemorrhage has an incredibly varied clinical presentation 1-3. The most commonly reported presenting symptom is a seizure, however, patients may present with apnea (in neonates and infants), focal neurological deficits, and headache 1-3.
On lumbar puncture and cerebrospinal fluid analysis, one case series found that no patients with subpial hemorrhage had evidence of fresh blood or xanthochromia 2.
Pathology
Subpial hemorrhage denotes the presence of blood in a potential space between the cortical surface and the pia mater 1-4. This potential space is somewhat controversial because pathological studies have not confirmed the existence of a ‘space’ as such, despite there being pathologically-proven cases of subpial hemorrhage 1. It is generally considered that between the pia mater and cortical surface is the glia limitans, which is the outermost layer of neural tissue consisting of astrocytic foot processes 1. Bleeding into this layer creates a ‘space’ and is thought to be the pathological basis of subpial hemorrhage 1.
Etiology
The etiology of subpial hemorrhage is also a subject of contention. Hypotheses from case series as to the etiology of subpial hemorrhage include:
- hemorrhage originating in the outermost layer of the cerebral cortex that extends into the glia limitans and thus into the subpial ‘space’ 1
- cortical vein thrombosis or congestion, evidence for this is the observation in one case series of subpial bleeds occurring in venous distributions 2
- trauma, especially birth trauma in neonates, although not considered to be a common etiology 3,4
Location
The most commonly involved lobe of the brain is the temporal lobe 7. Depending on the etiology, subpial hemorrhage may co-occur with other intracranial hemorrhages, such as intraparenchymal and subarachnoid hemorrhages 1-3.
Radiographic features
Subpial hemorrhage can be appreciated with CT and MRI, however, MRI is thought to be the superior modality. Typically, it has the radiographic appearance of blood along the cortical surface 1-3.
This entity can be difficult to distinguish from convexity subarachnoid hemorrhage, however, there are some subtle distinguishing features:
- subpial hemorrhage tends to be localized and may pool at the cortical surface, rather than spread along the convexity as seen in convexity subarachnoid hemorrhage 3
- acutely, subpial hemorrhage may be relatively more hyperdense on CT or hyperintense on T2 FLAIR MRI than subarachnoid blood, as subpial blood does not mix with cerebrospinal fluid 2
- there may be underlying cortical edema or restricted diffusion seen in association with subpial hemorrhage, which may not be seen in convexity subarachnoid hemorrhage 1,6
Treatment and prognosis
Treatment is conservative with symptomatic management (e.g. antiseizure medications). In case series of both pediatric and adult populations, the prognosis was generally good, with most patients having no or only mild neurological deficits upon follow-up 1-3.
History and etymology
The first case series of subpial hemorrhage was reported by Reinhard L Friede in his 1972 seminal paper 5.