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James Caldwell on The Hidden Culprit in Perimesencephalic SAH

James Caldwell/LinkedIn

Jan 9, 2026, 06:12

James Caldwell on The Hidden Culprit in Perimesencephalic SAH

James Caldwell, Interventional Neuroradiologist at Auckland City Hospital, shared on LinkedIn:

”When I went to school, I was taught that benign perimesencephalic subarachnoid hemorrhage (SAH) was most likely venous in origin—but the lack of direct evidence for a venous source always bothered me.

Later, I learned about basilar perforator aneurysms: “rare”, typically tiny aneurysms arising from basilar perforators that can present with SAH.

More recently, at our weekly neurovascular multidisciplinary meetings, we’ve repeatedly joked that “all” benign perimesencephalic hemorrhages are probably due to tiny or transient basilar perforator aneurysms that we never detect.

Well, some astute colleagues have shared a few compelling example cases at the page below – strongly recommend checking them out.

I read the page recently and it struck me like a chord.

What proportion of benign perimesencephalic SAH might be attributable to these lesions?

The page also highlights again what a valuable and deeply subspecialized resource neuroangio.org is.

Thank you to Maksim Shapiro et al!”

Find the full article here.

James Caldwell on The Hidden Culprit in Perimesencephalic SAH