Diffuse Calvarial Hyperostosis in Patients with Spontaneous Intracranial Hypotension.

Background: Diagnosis of spontaneous intracranial hypotension (SIH) may be delayed due to nonspecific symptoms and variable imaging findings. Cases of hyperostosis in children who are overshunted, a process that may be physiologically analogous to adults with SIH, have been reported by others and observed in our practice. The purpose of this retrospective study was to assess the frequency and pattern of calvarial hyperostosis in patients with SIH.

Methods: We retrospectively reviewed computed tomography and magnetic resonance imaging examinations from consecutive patients who underwent myelography for the evaluation of SIH to assess for the presence of generalized calvarial thickening or development of a secondary layer of bone. Patients with typical benign hyperostosis frontalis were excluded. Patient demographics and clinical factors were evaluated for association with hyperostosis.

Results: Among 285 patients with SIH, 40 (14.0%) demonstrated diffuse calvarial hyperostosis on imaging. Most of these patients (32/40; 80.0%) demonstrated a distinct circumferentially layered appearance to the skull, whereas 8 of 40 (20.0%) had generalized calvarial thickening without layering.

Conclusions: Diffuse calvarial hyperostosis, particularly the concentrically layered form that we term "layer cake skull," is a relatively common imaging feature in patients with SIH. In the appropriate clinical context, this finding will allow the possibility of SIH to be raised based on computed tomography imaging, which is otherwise of limited utility in the initial diagnosis of this condition.