The Source for Neurovascular News and Education

August 15, 2020

High BMI is protective during coiling and detrimental during clipping, an interplay possibly mediated by cerebral hypodensities

Among patients undergoing clipping for aneurysmal subarachnoid hemorrhage, having an elevated body mass index (BMI) is independently associated with poor outcome. Paradoxically, in the context of endovascular coiling, high BMI is independently linked to better outcome, researchers reported recently in the Journal of Neurosurgery.

“The association between BMI and outcome after aneurysmal subarachnoid hemorrhage has been investigated previously, with at times conflicting results,” lead author Lorenzo Rinaldo, MD, PhD (Mayo Clinic, Rochester, MN), told Neurovascular Exchange in an email. “Our study examined the effect of BMI on outcome when patients were stratified according to treatment modality, which to my knowledge has only been done in one other study.”

Rinaldo and colleagues reviewed outcomes, based on BMI, for patients admitted to their institution for the management of aneurysmal subarachnoid hemorrhage using either clipping (n = 144) or coiling (n = 325). Cutoff values for “high” versus “low” BMI were determined by classification and regression tree analysis.

Among patients treated with clipping, a greater proportion had a poor functional outcome (defined as 90-day mRS > 2) if they had a BMI of at least 32.3 kg/m2. The exact opposite pattern was seen among patients treated using coiling.

Poor 90-Day Functional Outcome by BMI and Treatment Type



High BMI

P Value

Treated With Clipping




Treated With Coiling



< 0.001


Multivariate analysis confirmed that high BMI predicted increased likelihood of poor functional outcome among patients undergoing clipping (OR 3.92; 95% CI 1.20-13.41; P = 0.024) but decreased likelihood of poor functional outcome among patients undergoing coiling (OR 0.13; 95% CI 0.03-0.40; P < 0.001) 

Role of Cerebral Hypodensities

For patients who underwent clipping, having a BMI ≥ 28.4 kg/m2 was independently associated with incidence of cerebral hypodensities during admission (OR 2.44; 95% CI 1.16-5.25; P = 0.018). For patients treated with coiling, having a BMI ≥ 33.2 kg/m2 was independently associated with reduced odds of hypodensities (OR 0.45; 95% CI 0.21-0.89; P = 0.021).

“The mechanism behind the effect of BMI remains poorly understood,” noted Rinaldo. “An obesity paradox has been described in multiple clinical contexts related to cerebral ischemia—mainly that obese patients have been observed to be less likely to suffer strokes, attain better functional outcomes after strokes, and are less likely to suffer recurrent strokes, though this is controversial. An obesity paradox may be going on in patients treated with coiling.”

He pointed out that obese patients treated with coiling were less likely to suffer cerebral infarcts during convalescence and speculated that obesity may exacerbate venous hypertension during intracranial surgery, which could in turn increase the risk of perioperative ischemia and infarction. All of this requires further exploration, he said.

Rinaldo acknowledged that the findings need to be confirmed, particularly given that this is a retrospective, single-center study. Nevertheless, he added, “they may be of use in the determination of treatment modality for patients with ruptured aneurysms, specifically that clipping may be higher risk than usual in patients with high BMI and thus should be reconsidered.”



Rinaldo L, Hughes JD, Rabinstein AA, et al. Effect of body mass index on outcome after aneurysmal subarachnoid hemorrhage treated with clipping versus coiling. J Neurosurg. 2017;Epub ahead of print.



Rinaldo reports no relevant conflicts of interest.