Original ArticleDiffuse Calvarial Hyperostosis in Patients with Spontaneous Intracranial Hypotension
Introduction
Spontaneous intracranial hypotension (SIH) is a neurologic syndrome caused by leakage of spinal fluid from the thecal sac of the central nervous system without an iatrogenic cause such as surgical violation of the dura or penetrating trauma.1,2 SIH can occur in the setting of normal cerebrospinal fluid (CSF) pressure, and as such some experts prefer the term CSF hypovolemia. The classic presentation of SIH is orthostatic headache, but many patients present with less obvious symptoms such as non-positional headache, dizziness, visual issues, ataxia, and cognitive impairment.3 Because the manifestations of SIH may be quite nonspecific, the condition cannot be diagnosed on clinical grounds alone, and imaging is indispensable to accurate diagnosis and effective treatment.
Imaging of SIH plays 2 major roles, the first being to suggest the diagnosis1 and the second being to localize the causative CSF leak to allow focused treatment2,4,5 In terms of initial diagnostic imaging, magnetic resonance imaging (MRI) of the brain with gadolinium is the most useful examination, typically demonstrating diffuse pachymeningeal enhancement, downward displacement of the hindbrain, colloquially known as brain sagging, or both. Currently, there is relatively little role for computed tomography (CT) in the initial diagnosis of SIH. CT examinations of the brain are often performed without intravenous contrast and are thus relatively insensitive to the dural changes. Severe cases of brain sagging are occasionally evident on CT, particularly if sagittal reconstructions are obtained, but this may be difficult to assess confidently. Because CT is frequently the first imaging modality used in the evaluation of neurologic symptoms, and because it may be the only modality available in some resource-limited settings, a reliable CT sign of SIH would be useful and likely to positively impact patient care.
Hyperostosis frontalis interna is a benign and almost always asymptomatic thickening of the inner table of the frontal bone, most commonly seen in postmenopausal women.6,7 Diffuse hyperostosis has been described in children with CSF shunts who are overshunted, a process physiologically analogous to SIH.8, 9, 10 Diffuse hyperostosis in patients with SIH has been observed in our clinical practice. The purpose of this retrospective study was to assess the frequency and pattern of calvarial hyperostosis in patients with SIH.
Section snippets
Patient Identification and Study Design
Institutional review board approval with waived consent was obtained for this HIPAA (Health Insurance Portability and Accountability Act)-compliant retrospective research study. A search of the radiology information system identified all patients with clinical suspicion of SIH who were referred for CT myelography to evaluate for spinal CSF leak between March 2002 and September 2014. Subspecialty board-certified neuroradiologists (median time since fellowship completion 6.5 years, range 2–7
Study Population
A total of 285 unique patients underwent CT myelography for evaluation of SIH during the period of interest. In total, 179 of 285 (62.8%) of the patients were female. Median age at time of first myelogram was 50.8 years (interquartile range [IQR] 42.6–60.2 years).
Hyperostosis Identification
On initial review, 59 of 285 (20.7%) of the patients demonstrated a possible or definite calvarial abnormality and were identified for further analysis. Of these, 40 of 59 (67.8%) of patients, or 40 of 285 (14.0%) overall, were
Discussion
This large retrospective study identifies diffuse calvarial hyperostosis as a relatively frequent imaging finding in patients with SIH. The most common form of hyperostosis encountered in this patient population is a circumferential layer of new bone formation along the inner table of the cranium, an appearance that we call “layer cake skull” (Figure 4). While hyperostosis can be an incidental finding on imaging, it is most often seen in postmenopausal women,11 whereas one-half of patients with
Conclusions
Diffuse calvarial hyperostosis, particularly the concentrically layered form that we term layer cake skull, is a relatively common and heretofore unrecognized imaging manifestation of presumed SIH. In the appropriate clinical context, identification of this imaging sign may allow neurosurgeons, neurologists, and radiologists to suggest the possibility of SIH and expeditiously obtain appropriate confirmatory testing. In patients with non-classic symptoms and/or equivocal MRI findings of SIH, the
CRediT authorship contribution statement
Derek R. Johnson: Conceptualization, Methodology, Data curation, Formal analysis, Writing - original draft, Writing - review & editing. Carrie M. Carr: Conceptualization, Methodology, Data curation, Formal analysis, Writing - review & editing. Patrick H. Luetmer: Conceptualization, Methodology, Data curation, Formal analysis, Writing - review & editing. Felix E. Diehn: Writing - review & editing. Vance T. Lehman: Writing - review & editing. Jeremy K. Cutsforth-Gregory: Writing - review &
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Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.