A case of Chiari III malformation associated with an occipitocervical meningomyeloencephalocele

Clinical History

The patient was referred with a swelling at the back of the craniocervical junction and hydrocephalus at birth.

Imaging Findings

The patient was referred with a swelling at the back of the craniocervical junction and hydrocephalus at birth. A cerebral MRI study was performed with SE T1, FSE T2, and FLAIR sequences in three planes on a 1.5 T MR scanner. MRI study was the first diagnostic modality applied for tha patient. A small posterior fossa volume with low-lying transverse sinuses was detected. There was a heart-shaped incisura with hypoplastic tentorium cerebelli. Additional posterior fossa findings were tectal beaking, creeping of the cerebellar hemispheres around the brain stem, and elongated tube-like narrowed inferiorly located fourth ventricle. A triventricular hydrocephaly was present, associated with colpocephaly. A coincidental cavum septum pellucidum et vergae variation was also detected apart from the pathological findings. Corpus callosum was dysgenetic. Herniation of dysplastic medulla oblongata and upper cervical spinal cord through an osseous defect of the lower occipital bone and posterior elements of the C1 and C2 cervical vertebrae was the major MRI finding, which was also correlated during the surgery. The patient underwent surgery for the repair of meningocele, and he is still under the medical control.

Discussion

Chiari III malformation is a rare abnormality that is characterised by the herniation of posterior fossa contents (cerebellum, and sometimes brainstem and fourth ventricle) and/or upper cervical spinal contents through a low occipital and/or upper cervical osseous defect. Chiari described a single case of caudal medullary displacement and cerebellar herniation, initially through the foramen magnum, then dorsally through a cervical spina bifida, resulting in a cervical encephalocele in his initial report of 1891. Since that time, the definition of Chiari III malformation has been expanded by some authors to include cases of hindbrain herniation into cephaloceles which encompass both the low occipital and upper cervical regions. It is a rare abnormality, as reported in the literature, and it is expected to show findings related to Chiari II malformation (Arnold-Chiari malformation) as well. These findings apart from those described in the clinical history of our patient are fenestrated falx cerebri, cerebellar hypertrophy, herniation of cerebellar tonsils into the foramen magnum, deformed mesencephalon, syringomyelia, aberrant draining veins and ectopic venous sinuses. Agenesis of posterior cervical vertebral elements, and concave clivus and petrous bone are associated bony anomalies.

Histopathological examination of occipitocervical cephaloceles reveals many associated anomalies such as necrosis, gliosis, heterotopias, and meningeal fibrosis, most of which could not be evaluated by medical imaging modalities.

Differential Diagnosis List

Final Diagnosis

Chiari III malformation

URL:	https://eurorad.org/case/1324
DOI:	10.1594/EURORAD/CASE.1324
ISSN:	1563-4086