Dilating the dogma of vasospasm

ROBERT LOCH MACDONALD

Angiographic vasospasm occurs in about two thirds of patients after aneurysmal SAH. Delayed infarction occurs in about a third. For decades the second was attributed to the first, and enormous resources have gone into preventing or reversing the narrowing. This talk, recorded at the Brain symposium in Sydney in March 2023, makes the argument the field has been avoiding: vasospasm can only damage the brain by limiting flow, we cannot measure flow or oxygen extraction in the tissue that matters, and so the attribution of ischaemia to spasm is, in the end, subjective.

The consequence is that we focus on vasospasm because it is the one delayed phenomenon we can detect, and then apply induced hypertension and angioplasty, whose side effects are underestimated, to patients who may have no region of brain with impaired oxygen delivery at all.

The argument in brief

• Cerebral infarction after SAH has many causes. The most common is the aneurysm repair procedure itself.

• Hypodensities directly under thick clot, where the brain simply dies, point to cortical spreading depolarisation rather than large-vessel spasm.

• Microthromboembolism, microcirculatory change, delayed apoptosis and capillary transit time heterogeneity are all plausible, and all undetectable at the bedside.

• Induced hypertension and angioplasty have never been tested in adequate, well-controlled trials. There is equipoise. Patients should be randomised, not treated by postcode.

Where this shows up in the program

This is the argument the Thursday afternoon session is built around. Jens Dreier presents on cortical spreading depolarisations and multimodal monitoring, Alex Choi on the adaptive immune system and DCI, Isabel Hostettler on early brain injury, and Loch Macdonald leads the panel on new directions for DCI treatment. Julian Maingard’s Thursday morning session on CT perfusion is, in effect, about whether we finally have a bedside way to tell flow-limiting spasm from the rest.

The trial question gets its own morning on Friday: Shane English on why so many aSAH trials have failed, Carolina Maciel and Katharina Busl on moving SAH research beyond single mechanisms, and Craig Anderson and Nerissa Ko debating whether platform and registry designs are the future or a false dawn. The randomised trial this talk calls for is exactly what those sessions are trying to make possible.

Read the full argument and references on NeuroResus.

ISAH 2026 runs 17–20 November at the Sheraton Grand Hyde Park, Sydney. See the program or register here.