Chiari Malformation (Arnold-Chiari Malformation)
Chiari malformation is a congenital anomaly in which the lower part of the cerebellum (cerebellar tonsils), and sometimes the brainstem, descends through the large opening at the skull base (foramen magnum) into the spinal canal. By disrupting cerebrospinal fluid circulation it can lead to syringomyelia and hydrocephalus; symptomatic cases are treated with surgical decompression.
Última actualización: 2026-06-07
Definition
Chiari malformation is a congenital anomaly defined by displacement (herniation) of the cerebellar tonsils—the lower part of the cerebellum—and, in some types, the brainstem, through the foramen magnum at the skull base into the spinal canal. In the most common form, Type 1, the cerebellar tonsils descend below a defined threshold and usually cause symptoms in late childhood or adulthood. Type 2 (Arnold-Chiari) occurs together with spina bifida and is recognized earlier. This displacement can obstruct cerebrospinal fluid (CSF) circulation at the foramen magnum, predisposing to syringomyelia (a cyst within the spinal cord) and hydrocephalus.
Causes and Risk Factors
Type 1 Chiari is most often associated with a small posterior fossa that leaves insufficient room for the cerebellum; most cases are sporadic with no clear genetic cause. Familial predisposition is reported in a minority. Type 2 Chiari occurs with the neural tube defect spina bifida, and folic acid deficiency during pregnancy is a known risk factor.
Symptoms
The most characteristic symptom is a headache felt in the nape and back of the head that worsens with coughing, sneezing, or straining (the Valsalva maneuver). It may be accompanied by neck pain, balance and coordination problems (ataxia), numbness and weakness in the hands, difficulty swallowing, double or blurred vision, ringing in the ears, dizziness, and sleep apnea. When syringomyelia develops, back and arm pain and—particularly in children—scoliosis may appear. Many Type 1 cases are silent and found incidentally.
Diagnosis
The gold standard for diagnosis is magnetic resonance imaging (MRI), which shows the cerebellar tonsils descending below the foramen magnum and any associated syringomyelia. In addition to sagittal and axial images, a CSF flow study (phase-contrast/cine MRI) assesses the flow disturbance at the foramen magnum and guides surgical planning. Computed tomography helps evaluate the bony structures and posterior fossa anatomy. Electrophysiological tests may be used to gauge spinal cord involvement.
Treatment
Treatment is guided by the presence and severity of symptoms. Incidentally found, asymptomatic Type 1 cases are usually followed with periodic MRI and neurological examination. The standard procedure in symptomatic patients is posterior fossa decompression: removing part of the back of the skull (suboccipital craniectomy) and the posterior arch of the first cervical vertebra (C1 laminectomy) to create room for the cerebellum and brainstem. For wider decompression the dura may be opened and enlarged with a patch (duraplasty). Associated syringomyelia usually regresses on its own after decompression; a shunt may be needed if hydrocephalus is present.
Prognosis
In appropriately selected patients, a large proportion of symptoms improve or stabilize after surgical decompression; Valsalva-triggered headache in particular can decrease markedly. Motor and sensory symptoms and syringomyelia regress gradually over months. Early diagnosis and treatment are important to prevent permanent spinal cord damage. In some patients symptoms may persist or, rarely, repeat surgery may be needed; outcomes are individual and none can be guaranteed.
Referencias
- Greenberg MS. Greenberg's Handbook of Neurosurgery. 10th ed. Thieme; 2023:295-308.
- Winn HR, ed. Youmans Neurological Surgery. 6th ed. Saunders; 2011.
- Milhorat TH, et al. Chiari I malformation redefined: clinical and radiographic findings. Neurosurgery. 1999.
Este artículo es informativo y no sustituye un examen médico. Las decisiones de diagnóstico y tratamiento son individuales.