Objective: Intracranial pressure (ICP) over 20 mmHg is associated with poor neurologic prognosis, but measuring ICP directly requires an invasive procedure. Dilation of the optic nerve sheath on axial ultrasound of the eye has been correlated with elevated ICP, but optimal cutoffs have been inconsistent possibly related to the measurement technique. A coronal technique has been studied on healthy volunteers but not on patients with high ICP. We compared two measurement techniques (axial and coronal) in patients with suspected high ICP due to trauma, bleeding, tumor, or infection.Design: Prospective blinded observational study.Setting: Two tertiary referral center intensive care units.Patients: 20 adults admitted to the ICU at risk for increased ICP expected to receive invasive intracranial monitoring.Interventions: Ultrasound measurements of the optic nerve sheath in axial and coronal views either averaged between eyes or the highest in either eye. Measurements and Main Results:Coronal measurements showed less variability between each eye than axial measurements (mean difference 0.5mm vs. 1mm, p=0.03) and were associated with high ICP at first measurement and over 24 hours (AUROC range 0.7 to 0.8). Mean and highest axial measurements showed improved association with first (AUROC 0.87, 0.94) and highest ICP measurement (AUROC 0.89, 0.96) within 24 hours. A cutoff of highest axial measurement in either eye greater than 6.2mm or mean axial measurement between eyes of 5.6mm had a sensitivity of 100% in predicting high ICP over the following 24 hours.

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Background: Non-headache literature inevitably influences headache research, but the way this interdisciplinary interaction occurs has seldom been evaluated. Objective: Utilizing network analysis techniques within the PubMed Central (PMC) database, we illustrate a novel method by which to identify and characterize the important non-headache literature with significant impact within the headache world. Methods: Using the National Center for Biotechnology Information E-utilities application programing interface and custom backend software, all PMC articles containing the words "headache(s)" and/or "migraine(s)" in the title were identified. This generated a list of "seed articles" to represent the body of primary headache literature. Articles referenced by the seeds were then found, generating the list of articles with one degree of separation from the seeds (first-degree neighbors). This was iterated twice more to find the second-and third-degree neighbors. A directed network graph was generated for each level of separation using these articles and their referential connections. The hyperlink-induced topic search (HITS) and PageRank algorithms were used on these graphs to find the top 50 articles in the network (hub and authority rank via HITS, general rank via PageRank). Removing seed articles from the ranked lists left the influential non-headache articles at each level of separation. Results: We extracted 6890 seed articles. The first-, second-, and third-degree models contained 16,451, 105,496, and 431,748 articles, respectively. As expected, most first-degree neighbors were part of the seed group (headache literature). Using HITS, at the second degree, only two seed articles were found in the top 50 hubs (none in the authorities); the majority of non-seed articles were basic neuroscience, involving ion channel function or cell signaling. At the third degree, there were no seeds and all articles involved imaging/structure of brain connectivity networks. PageRank gave more varied results, with 35/50 second-degree articles being seeds, and the remainder a mixture of articles describing rating scales (3), epidemiology/disease burden (3), basic statistical/trial methods (3), and mixed basic science (6). At the third degree, five were seeds; non-seed articles were represented heavily by genomic mapping studies, brain connectivity networks, and ion channel/neurotransmitter studies. Conclusion: This work demonstrates the value of network citation analysis in the identification of interdisciplinary influences on headache medicine. Articles found with