Traumatic subarachnoid hemorrhage

Traumatic subarachnoid haemorrhage (TSAHtSAH) is a common injury, and trauma is the most common cause of subarachnoid haemorrhage (SAH). 

Epidemiology

TSAHTraumatic subarachnoid haemorrhage occurs in ~35% (range 11-60%) of traumatic brain injuries ¹. 

Pathology

TSAHTraumatic subarachnoid haemorrhage is most commonly seen in the cerebral sulci than in the Sylvian fissure and basal CSF cisterns ¹. When in the basal cisterns, it has an affinity for the quadrigeminal cistern and ambient cistern ². TSAHtSAH is also commonly seen adjacent to skull fractures and cerebral contusions ³. 

Radiographic features

CT is consideredof the best modality for detectionbrain is almost always the first scan obtained int he setting of TSAH duetrauma, often as part of a CT panscan. 

Although the sensitivity of CT to its high sensitivitythe presence of subarachnoid blood is strongly influenced by both the amount of blood and ready availability. MRI is less sensitive for detecting subarachnoidthe time since the haemorrhage, in the setting of trauma scans are almost always obtained early, often mere minutes or hours from head injury, making even small amounts of blood readily visible. 

The distribution and amount of blood varies greatly depending on the underlying mechanism (see above) and from patient to patient.

Often a small amount of blood is seen filling a few sulci, sometimes with SWI¹an adjacent cerebral contusion. Please see main subarachnoid haemorrhage article Small amounts of blood can also sometimes be appreciated pooling in the interpeduncular fossa, appearing as a small hyperdense triangle, or within the occipital horns of the lateral ventricles.

Occasionally, and worrying for further detailsan underlying arterial dissection or an aneurysmal haemorrhage that preceded trauma, larger amounts of blood may be seen around the circle of Wilis and within the posterior fossa. 

Treatment and prognosis

TSAHTraumatic subarachnoid haemorrhage has a better prognosis than aneurysmal SAH ². 

Complications

• cerebral vasospasm
• communicating hydrocephalus ²

Differential diagnosis

• aneurysmal SAH: can

   can be difficult to delineate from TSAH ³tSAH, particularly as in many instances the cause of head trauma may have been spontaneous subarachnoid (e.g. while driving). 

  The distribution of blood, particularly if closely related to cerebral contusions can suggest traumatic aetiology, whereas extensive blood around the circle of Willis should prompt arterial imaging to exclude an aneurysm. 

  Distinguishing between aneurysmal subarachnoid haemorrhage and traumatic non-aneurysmal subarachnoid haemorrhage is not always possible, and the trauma may have in reality been precipitated by a spontaneous aneurysmal haemorrhage (e.g. while driving).

  That having been said, there are helpful features in suggesting that subarachnoid haemorrhage is the result of trauma, rather than the reason for trauma. These features include: 

  1. documented (witnessed) trauma not being preceded by a headache or loss of consciousness or seizure