Angiographic features of “brain sag”

Clinical article

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Cerebrospinal fluid hypotension, or “brain sag,” is a recently described phenomenon most commonly seen following craniotomy for the clipping of ruptured aneurysms along with preoperative lumbar drain placement. The clinical features and CT findings have been previously described. Clinical presentation can be similar to and often mistaken for cerebral vasospasm. In this study, the authors report on the angiographic findings in patients with brain sag.


Five cases of brain sag were diagnosed (range 1–4 days) after the surgical treatment of ruptured aneurysms at the University of Illinois at Chicago. All patients met the clinical and CT criteria for brain sag. Admission cerebral angiograms and subsequent angiograms during symptoms of brain sag were obtained in all patients. In 3 patients, angiography was performed after the resolution of symptoms.


In all 5 patients, the level of the basilar artery apex was displaced inferiorly with respect to the posterior clinoid processes during brain sag. This displacement was significant enough to create a noticeable kink in the basilar artery (“cobra sign”) in 3 patients. Other angiographic findings included foreshortening or kinking of the intracranial vertebral artery. In all patients, the posterior cerebral arteries were displaced medially and inferiorly. Three patients were treated for simultaneous severe radiological vasospasm. In 4 patients, the brain sag was recognized, and the patients' conditions improved when they were placed flat or in the Trendelenburg position, at times combined with an epidural blood patch. Patients with follow-up angiography studies after the symptoms had resolved displayed a reversal of the angiographic features.


Brain sag appears to be associated with characteristic angiographic features. Recognizing these features may help to diagnose brain sag as the cause of neurological deterioration in this patient population.

Abbreviations used in this paper: ACoA = anterior communicating artery; EVD = external ventricular drain; ICP = intracranial pressure; PCA = posterior cerebral artery; PICA = posterior inferior cerebellar artery; POD = postoperative day; SAH = subarachnoid hemorrhage; VA = vertebral artery.

Article Information

Address correspondence to: Ali Alaraj, M.D., Neuropsychiatric Institute (MC 799), Department of Neurosurgery, University of Illinois at Chicago, 912 South Wood Street, Chicago, Illinois 60612-5970. email:

Please include this information when citing this paper: published online May 27, 2011; DOI: 10.3171/2011.4.JNS101168.

© AANS, except where prohibited by US copyright law.



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    Case 1. Admission CT scan (left) demonstrating diffuse SAH and early hydrocephalus. Follow-up CT scan (right) obtained at the onset of symptoms of brain sag, showing an oblong appearance of the brainstem.

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    Case 1. Anteroposterior (A) and lateral angiograms (B) obtained at baseline, showing normal arterial anatomy and the relationship of the basilar tip to the posterior clinoid process. Angiograms obtained during brain sag (C and D), showing medial and inferior descent of the PCAs (curved arrow), descent of the basilar tip (arrowhead) with respect to the posterior clinoid process, kinking of the basilar artery (small arrow), kinking of the intradural portion of the VA (large arrow), and change in the configuration of the PICA. Follow-up angiogram obtained 2 weeks later, showing resolution of the features of brain sag (E).

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    Case 3. Oblique cerebral angiograms obtained on presentation (left) and during brain sag (right), showing inferior displacement of the basilar tip (arrowhead), medial and inferior displacement of the PCAs (curved arrow), lateral kinking of the midbasilar segment (small arrow), and kinking of the intradural portion of the left VA (large arrow).

  • View in gallery

    Illustration depicting medial and inferior displacement of both PCAs, descent of the basilar tip with respect to the posterior clinoid process, kinking of the midbasilar artery, and kinking of the intracranial VAs (black) as compared with normal vasculature (gray).


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