Perimesencephalic hemorrhage: a proposed explanation of its cause and clinical manifestations

J Neurosurg 144:740–746, 2026

This neurosurgical forum article analyzes perimesencephalic hemorrhage (PMH), proposing that small dural arterial variants—particularly the artery of Wollschlaeger and Wollschlaeger (AWW) arising from the superior cerebellar artery—can undergo distraction-avulsion and explain PMH’s characteristic cisternal distribution and benign clinical course. The authors present a surgical case with intraoperative identification of an SCA-derived dural branch and perform detailed anatomical correlation.

The paper contrasts venous and arterial hypotheses, reviews perimesencephalic cisternal anatomy and tentorial blood supply, and argues that spontaneous tearing of a tethered intradural dural branch best accounts for imaging, pathophysiology, and low recurrence of PMH, while acknowledging limits of confirmatory testing.

PMH profile Nonaneurysmal perimesencephalic hemorrhage (PMH) is ~10%–15% of spontaneous cisternal SAH, with CT blood confined around the midbrain and typically a benign course with complete recovery and rare recurrence.

Unknown etiology Despite decades of imaging/anatomical work, the cause often remains unidentified on initial and follow-up angiography, leading to the concept of “SAH of unknown cause,” especially when bleeding is perimesencephalic-only.

Index case A 54-year-old woman with SAH had angiography showing a dural arteriovenous fistula (DAVF) fed by the meningohypophyseal trunk and draining via the superior petrosal vein; surgery disconnected the fistula with good outcome.

Unexpected anatomy Intraoperatively, a dural branch from the superior cerebellar artery (SCA) was found bridging the ambient cistern to the undersurface of the tentorium (the artery of Wollschlaeger and Wollschlaeger, AWW) and was sacrificed; it had not been seen on preop angiography and was not the hemorrhage source in that case.

Key anatomical concept The perimesencephalic cistern system (interpeduncular, ambient, quadrigeminal) surrounds the midbrain at the tentorial incisura; vessels can traverse cisternal spaces and arachnoid septations, influencing where blood can collect.

Tentorial dural supply variants The medial tentorium can be supplied by the marginal tentorial artery from the meningohypophyseal trunk, plus intradural-origin dural branches from the PCA (artery of Davidoff and Schechter, ADS) and from the SCA (AWW) that course within the ambient cistern before entering tentorium.

Competing sources considered Two structures fit many PMH constraints: the basal vein of Rosenthal (BVR) (venous, tethered to vein of Galen) and the ADS/AWW (arterial dural branches tethered to the medial tentorial edge).

Proposed mechanism for PMH Spontaneous distraction-avulsion of the AWW from its fragile tentorial attachment during everyday Valsalva/exertion could cause focal cisternal bleeding that self-limits as pressure equalizes in the confined cistern; this is proposed to explain PMH distribution, negative angiography, generally mild course, low hydrocephalus/vasospasm, and rare rebleed.