February 10, 2020 e-Pearl of the Week: Perimesencephalic Subarachnoid Hemorrhage (PMSAH)

Perimesencephalic Subarachnoid Hemorrhage (PMSAH)

Perimesencephalic Subarachnoid Hemorrhage (PMSAH) is characterized by blood accumulation which is limited to the subarachnoid space around the midbrain1—anteriorly or posteriorly—in the quadrigeminal or pretruncal cistern3 with a comparatively benign prognosis. It represents 5% of all SAH2 and ~33% of all non-aneurysmal SAH, with only 2–9% of PMSAH occurring due to ruptured posterior circulation saccular aneurysms, a theory that is supported by the low rate of subsequent re-bleeding.4 There are competing hypotheses regarding its etiopathogenesis, including: rupture of posterior circulation perforating artery, leakage of blood from susceptible vein,1 or a basilar artery wall hematoma. Symptoms of sudden-onset headache, meningism, and transient focal deficits are similar to aneurysmal SAH but less severe, as objectively demonstrated with lower Hunt and Hess grades and lower rates of loss of consciousness.4,5 Non-contrast CT scan—to identify characteristic pattern of bleed—and cerebral angiography—to rule out aneurysms—are the imaging modalities of choice.6 Treatment is supportive with excellent prognosis.4–6

References

  1. van Gijn J, van Dongen KJ, Vermeulen M, Hijdra A. Perimesencephalic hemorrhage: a nonaneurysmal and benign form of subarachnoid hemorrhage. Neurology 1985;35:493–497. 
  2. Flaherty ML, Haverbusch M, Kissela B, et al. Perimesencephalic Subarachnoid Hemorrhage: Incidence, Risk Factors, and Outcome. J Stroke Cerebrovasc Dis 2005;14:267–271.
  3. Schwartz TH, Mayer SA. Quadrigeminal variant of perimesencephalic nonaneurysmal subarachnoid hemorrhage. Neurosurgery 2000;46:584–588.
  4. Şahin S, Delen E, Korfali E. Perimesencephalic subarachnoid hemorrhage: Etiologies, risk factors, and necessity of the second angiogram. Asian J Neurosurg 2016;11:50–53.
  5. Ildan F, Tuna M, Erman T, Göçer AI, Cetinalp E. Prognosis and prognostic factors in nonaneurysmal perimesencephalic hemorrhage: a follow-up study in 29 patients. Surg Neurol 2002;57:160–165.
  6. Mensing LA, Vergouwen MDI, Laban KG. Perimesencephalic Hemorrhage: A Review of Epidemiology, Risk Factors, Presumed Cause, Clinical Course, and Outcome. Stroke 2018;49:1363–1370.

Schweta Rane, Medical Graduate, Grant Government Medical College; and Faisal Khan, MD, DABSM, DABPN, Consultant Neurologist, Sugar Land Neurology and Sleep, Texas

Schweta Rane and Dr. Khan report no disclosures.