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  • Kevin M. Rice, MD

Pseudo-Subarachnoid Hemorrhage due to Leptomeningeal Carcinomatosis

Updated: Jul 26, 2021

Headache, Altered, Pancreas Cancer • Xray of the Week

This 61 year old female with a history of pancreatic cancer presented with altered mental status, and had a CT scan and MRI brain. A subsequent lumbar puncture revealed the diagnosis. What is the abnormality and what is the diagnosis?

Pseudo-Subarachnoid Hemorrhage due to Leptomeningeal Carcinomatosis

Upper row: CT brain without contrast. Note the high attenuation overlying the right cerebral convexity. There is no abnormality in the basal cisterns. Bottom left and right: T1 weighted images with contrast demonstrate abnormal leptomeningeal enhancement along the right cerebral hemisphere, over the right frontal lobe, parietal lobe, operculum, Sylvian fissure, and temporal lobe.

Bottom middle: T2* GRE image shows no blood products, with no region of low signal.

The history of pancreatic carcinoma and the lack of high attenuation material in the basal cisterns on the CT scan may give the reader a clue that the findings are not due to subarachnoid hemorrhage (SAH). The leptomeningeal enhancement on the MRI may be due to leptomeningeal carcinomatosis, meningitis, or other inflammatory processes. A subsequent lumbar puncture revealed pancreatic carcinoma on cytology. Therefore, the findings are due to leptomeningeal carcinomatosis.

Differential diagnosis of pseudo-subarachnoid hemorrhage on CT:


•Leptomeningeal carcinomatosis

•Artifacts on CT: anoxic encephalopathy, spontaneous intracranial hypotension

•Iatrogenic causes: recently administered intrathecal or IV contrast material; and following endovascular procedures such as aneurysm coiling and stroke intervention.

Highly proteinaceous material in the subarachnoid space causes increased attenuation which may be due to purulent fluid seen with meningitis or leptomeningeal carcinomatosis, mimicking SAH.

Anoxic encephalopathy and spontaneous intracranial hypotension both cause a perceptual error due to relatively higher attenuation of the basal cisterns related to the low attenuation seen with these conditions.

Iodinated contrast in the subarachnoid space either due to IV or intrathecal administration causes high attenuation in the subarachnoid space which should be easily differentiated from SAH if the history is known. Likewise, endovascular procedures may result in leakage of iodinated contrast which could be confused with SAH, especially given that the procedures are often done for patients with SAH or aneurysms. Follow up CT scan within 3-4 hours after the procedure will show clearing of the contrast, whereas SAH will persist.


1. Carrie P. Marder, et al. Subarachnoid Hemorrhage: Beyond Aneurysms. American Journal of Roentgenology. 2014;202: 25-37. 10.2214/AJR.12.9749

2. Mendelsohn DB, Moss ML, Chason DP, Muphree S, Casey S. Acute purulent leptomeningitis mimicking subarachnoid hemorrhage on CT. J Comput Assist Tomogr 1994; 18:126–128

3. Tsuchiya K, Katase S, Yoshino A, Hachiya J. FLAIR MR imaging for diagnosing intracranial meningeal carcinomatosis. AJR 2001; 176:1585–1588

4. al-Yamany M, Deck J, Bernstein M. Pseudo-subarachnoid hemorrhage: a rare neuroimaging pitfall. Can J Neurol Sci 1999; 26:57–59

Case courtesy of my friend and colleague Gregory P. Lekovic, M.D., Ph.D.

Kevin M. Rice, MD

Kevin Rice, MD serves as the Medical Director of the Radiology Department of Valley Presbyterian Hospital in Los Angeles, California and is a radiologist with Renaissance Imaging Medical Associates. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015 Dr. Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. Due to his online teaching activities, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator in 2016.

Follow Dr. Rice on Twitter @KevinRiceMD

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