{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,18]],"date-time":"2026-08-18T04:50:28Z","timestamp":1787028628904,"version":"build-2736575974"},"reference-count":95,"publisher":"MDPI AG","issue":"18","license":[{"start":{"date-parts":[[2022,9,17]],"date-time":"2022-09-17T00:00:00Z","timestamp":1663372800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Institute of Neurological Diseases and Stroke","award":["NIH ZIANS003052-15"],"award-info":[{"award-number":["NIH ZIANS003052-15"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["JCM"],"abstract":"<jats:p>Patients showing typical Chiari malformation type 1 (CM1) signs and symptoms frequently undergo cranial and cervical MRI. In some patients, MRI documents &gt;5 mm of cerebellar tonsillar herniation (TH) and the diagnosis of CM1. Patients with 3\u20135 mm TH have \u201cborderline\u201d CM1. Patients with less than 3 mm of TH and an associated cervical syrinx are diagnosed with Chiari \u201czero\u201d malformation (CM0). However, patients reporting CM1 symptoms are usually not diagnosed with CM if MRI shows less than 3\u20135 mm of TH and no syrinx. Recent MRI morphometric analysis of the posterior fossa and upper cervical spine detected anatomical abnormalities in and around the foramen magnum (FM) that explain these patients\u2019 symptoms. The abnormalities include a reduced size of the posterior fossa, FM, and upper cervical spinal canal and extension of the cerebellar tonsils around the medulla rather than inferior to the foramen magnum, as in CM1. These morphometric findings lead some neurologists and neurosurgeons to diagnose CM0 in patients with typical CM1 signs and symptoms, with or without cervical syringes. This article reviews recent findings and controversies about CM0 diagnosis and updates current thinking about the clinical and radiological relationship between CM0, borderline CM1, and CM1.<\/jats:p>","DOI":"10.3390\/jcm11185472","type":"journal-article","created":{"date-parts":[[2022,9,19]],"date-time":"2022-09-19T02:06:50Z","timestamp":1663553210000},"page":"5472","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":14,"title":["The Small Posterior Cranial Fossa Syndrome and Chiari Malformation Type 0"],"prefix":"10.3390","volume":"11","author":[{"given":"Enver I.","family":"Bogdanov","sequence":"first","affiliation":[{"name":"Department of Neurology and Rehabilitation, Kazan State Medical University, 420012 Kazan, Russia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Aisylu T.","family":"Faizutdinova","sequence":"additional","affiliation":[{"name":"Department of Neurology and Rehabilitation, Kazan State Medical University, 420012 Kazan, Russia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3890-0165","authenticated-orcid":false,"given":"John D.","family":"Heiss","sequence":"additional","affiliation":[{"name":"Surgical Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2022,9,17]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"444","DOI":"10.1016\/j.wneu.2020.01.147","article-title":"Ventrolateral Tonsillar Position Defines Novel Chiari 0.5 Classification","volume":"136","author":"Morgenstern","year":"2020","journal-title":"World Neurosurg."},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Tubbs, R.S., Turgut, M., and Oakes, W.J. 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