History and Physical
A 10-year-old previously healthy girl presents with headaches for the past 6 months. Headaches occur one to two times per week, with variable duration from several minutes to a few hours. They are bilateral in location, often occipital, and of moderate intensity (6-7/10) with no clear triggers. Symptoms improve spontaneously or with ibuprofen in prolonged cases. There is no associated vomiting, nausea, photophobia, phonophobia, or aura. No antecedent fever, trauma, or toxin exposure. Psychiatric evaluation excludes anxiety and depression. Family history is negative for migraine and recurrent headaches. Physical examination is normal. Patient returns 3 months later, following an episode of laryngotracheitis. She reports intense headaches during coughing spells and Valsalva maneuvers, different from the prior headaches. At this time, the headaches are more localized to the occipital region and remain variable in duration, from very brief to 1 hour. Again, the clinical and neurological examination is normal.
Diagnostic Workup
MRI demonstrates dysmorphic cerebellar tonsils located 10 mm below the foramen magnum (McRae line) and cervical cord syrinx ( Fig. 3.1A – C ). Phase contrast study confirms CSF flow obstruction at the level of the foramen magnum, both ventrally and dorsally ( Fig. 3.1D ).
Chiari I malformation with cervical cord syrinx. (A) Craniocervical junction MRI, (B) sagittal T1 and T2: dysmorphic cerebellar vermis and tonsils located 10 mm below skull base ( arrowheads ), with cervical cord syrinx from C7 to T1 ( arrows ). (C) Axial T2 shows cervical cord syrinx. (D) Sagittal phase contrast shows obstructed ventral and dorsal CSF flow through the craniocervical junction ( arrowheads ). CSF , Cerebrospinal fluid.
Clinical Differential Diagnosis
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Primary cough headache
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Chiari I malformation
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Intracranial hypotension
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Intracranial hypertension
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Intracranial hemorrhage
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Brain tumor
Imaging Differential Diagnosis
Inferior displacement of the cerebellar tonsils can be observed in a variety of normal and pathologic conditions. Cerebellar tonsillar ectopia refers to normal morphology but low positioning of the tonsils below the skull base. Though the normal measurements vary with age, most cases lie within approximately 5 mm of the basion-opisthion or McRae line ( Fig. 3.2 ), with the normal spectrum varying by age.
McRae line. Craniocervical junction MRI, sagittal T1 shows tonsillar descent ( dotted line ) below the basion-opisthion line ( solid line ) connecting the anterior and posterior margins of the foramen magnum.
Chiari I malformation refers to a developmental posterior fossa anomaly with descent and dysplasia of the cerebellar vermis and tonsils, creating a pointed appearance. In severe cases, there can be mass effect on the brainstem with a dorsal cervicomedullary kink. Simple Chiari I malformations are amenable to surgical decompression with suboccipital craniectomy. Complex Chiari I malformations are associated with additional bony abnormalities such as clival hypoplasia ( Fig. 3.3 ), platybasia, craniosynostosis ( Fig. 3.4 ), and odontoid variants ( Figs. 3.5 and 3.6 ), which can affect the surgical approach.
Chiari I malformation secondary to clival hypoplasia. Brain MRI, sagittal T1 with gadolinium shows Chiari I malformation. The posterior fossa pentagon connecting the clivus, McRae line, supraocciput, tentorium, and tentorium-clivus line ( lines ) shows a foreshortened and vertically oriented clivus.
Syndromic craniosynostosis due to Apert syndrome. Head CT, sagittal (A), and 3D reconstruction (B) show multisuture craniosynostosis with turribrachycephaly, skull base hypoplasia, decreased posterior fossa volume, and cerebellar crowding ( arrowhead ). Brain MRI, sagittal T1 (C) and T2 (D) show posterior fossa hypoplasia and crowding of the craniocervical junction ( arrows ).
Complex Chiari I with platybasia and odontoid retroversion. Brain MRI, sagittal T1 shows platybasia and odontoid retroversion ( arrowhead ) more than 9 mm behind the pBC2 line (maximum perpendicular distance from the line of the basion to the infero-posterior point of the vertebral body of C2) ( dotted and solid lines ). There is secondary posterior fossa crowding with dysmorphic pointed cerebellar tonsils.
