Chiari Malformation Type 1 in Adults

Abstract

The term Chiari malformation refers to a heterogeneous group of anatomical abnormalities at the craniovertebral junction. Chiari malformation type 1 (CM1) refers to the abnormal protrusion of cerebellar tonsils through the foramen magnum and is by far the commonest type. Its prevalence is estimated approximately 1%; it is more common in women and is associated with syringomyelia in 25-70% of cases. The prevalent pathophysiological theory proposes a morphological mismatch between a small posterior cranial fossa and a normally developed hindbrain that results in ectopia of the tonsils.In most people, CM1 is asymptomatic and diagnosed incidentally. In symptomatic cases, headache is the cardinal symptom. The typical headache is induced by Valsalva-like maneuvers. Many of the other symptoms are nonspecific, and in the absence of syringomyelia, the natural history is benign. Syringomyelia manifests with spinal cord dysfunction of varying severity. The approach to patients with CM1 should be multidisciplinary, and the first step in the management is phenotyping the symptoms, because they may be due to other pathologies, like a primary headache syndrome. Magnetic resonance imaging, which shows cerebellar tonsillar decent 5 mm or more below the foramen magnum, is the gold standard investigative modality. The diagnostic workup may include dynamic imaging of the craniocervical junction and intracranial pressure monitoring.The management of CM1 is variable and sometimes controversial. Surgery is usually reserved for patients with disabling headaches or neurological deficits from the syrinx. Surgical decompression of the craniocervical junction is the most widely used procedure. Several surgical techniques have been proposed, but there is no consensus on the best treatment strategy, mainly due to lack of high-quality evidence. The management of the condition during pregnancy, restriction to lifestyle related to athletic activities, and the coexistence of hypermobility require special considerations.

Keywords: Cerebellar tonsils; Cerebrospinal fluid; Chiari malformation; Craniovertebral junction; Foramen magnum decompression; Syringomyelia.