Low-pressure headaches following foramen magnum decompression secondary to absorption of cerebrospinal fluid into the venous system of the diploic space.

INTRODUCTION: We describe a case of a patient who suffered low-pressure headaches secondary to absorption of cerebrospinal fluid into the venous system of the diploic space following a foramen magnum decompression. This case is important as it describes a physiologically plausible but previously undescribed complication of a common surgical intervention. CASE: A nine-year-old boy underwent a foramen magnum decompression for a Chiari malformation (Type I). Five years after his initial decompression, his original symptoms returned and he underwent further decompression with short-term relief of symptoms. He then began to describe low-pressure headaches. Comprehensive investigations revealed a small posterior pseudomeningocoele that had extended into the diploic space at the site of the previous surgery to the occipital bone. It was postulated that the diploic space may be acting as an additional site for reabsorption of his CSF, and as a result of this, he was experiencing consistently low-pressure symptoms. His symptoms have completely resolved following surgical intervention to seal the site of communication with the diploic space. DISCUSSION: We review recent literature that supports this theory through an understanding of the anatomy of the diploic venous system and also its physiological behaviour as demonstrated in recent cadaveric and porcine studies.