Heterotopic Neural Tissue in the Dural Sinus: More Frequent than Usually Assumed?

We read with great interest the article by Kollar et al (1) describing the presence of heterotopic brain tissue in the transverse sinus with a concomitant dural fistula. We would strongly support the view that not all structures found within the dural sinuses are in fact arachnoid granulations as assumed by some authors (2, 3). We would like to direct AJNR readers to a case of increased intracranial pressure caused by an intrasinusal cystic structure which was surgically removed and histologically examined (4). As in the case of Kollar et al, we found heterotopic nervous tissue in the wall of a cyst. It was termed “hamartoma” in our article, and therefore may have escaped these authors' notice during their search of the literature. The lack of histologic evidence of the nature of intrasinusal structures is understandable because of the risk of surgically opening the sinus and the paucity of clinical symptoms in the majority of cases. We would, however, suggest that these structures be called what they are, lesions of unknown origin, rather than arachnoid granulations. Many cases in which histologic evidence could be attained yield arachnoid tissue findings (1).