Literature
Clinical Pearls & Morning Reports
Published June 19, 2024
What are some of the clinical and imaging features of adult Chiari malformation type 1?
With the wide availability of cerebral imaging, recognition of Chiari malformations has become common, and determining which patients have symptoms associated with the anatomical abnormality can be challenging. Read the NEJM Review Article here.
Clinical Pearls
Q: What is the most common type of Chiari malformation?
A: The most common type of Chiari malformation is adult Chiari malformation type 1 (CM1), in which the cerebellar tonsils (the most caudal part of the cerebellum) protrude below the lower margin of the foramen magnum. As the cerebellar tonsils protrude below the foramen magnum, obstruction of the foramina of Luschka and Magendie of the lower medulla and compression of the upper cervical spine may occur, impeding the flow of CSF from the fourth ventricle to the upper spinal subarachnoid space. In some instances, this is accompanied by a syrinx (cystic cavity), which is most commonly located in the cervical cord but can involve any part of the spinal cord and rarely the brainstem.
Q: Name some of the causes of cerebellar tonsillar herniation in adult CM1.
A: Although a congenitally small posterior fossa is the most common cause of cerebellar tonsillar herniation, acquired cerebellar descent can result from pressure gradients created by a pulling effect from below or a pushing effect from above. Pull from below the foramen magnum is the result of spinal CSF leakage, a CSF–venous fistula, or a tethered cord. Push from above the foramen magnum can result from hydrocephalus, subdural collections, a brain tumor, or an arachnoid cyst.
Morning Report Questions
Q: What are some of the clinical features of adult CM1?
A: Symptoms attributable to descent of the cerebellar tonsils into the foramen magnum vary. The most common symptom is headache, which is most likely due to transiently raised intracranial pressure from partial blockage of CSF flow. The headache is usually suboccipital and dull or throbbing, but it can be located anywhere in the cranium and have other characteristics, including migraine and tensionlike discomfort. Chiari headaches are characteristically exacerbated by Valsalva-like activities such as coughing, laughing, sneezing, straining, lifting heavy objects, and changing body or head positions. An additional symptom, which is independent of but often associated with headaches, is paresthesia in one or both hands, often involving all the fingers. Other less common but characteristic signs and symptoms include sleep apnea; tinnitus, which may be pulsatile; hypoacusis or hyperacusis; and difficulty swallowing. The spinal cord syrinx may be symptomatic or asymptomatic. Patients with a syrinx may present with complex symptoms that are independent of those directly caused by the tonsillar herniation — typically numbness or decreased pain or temperature sensitivity in the hands and over the shoulders, hand weakness and atrophy, and arm, leg, neck, or back pain, as well as bladder or bowel incontinence.
Q: How is adult CM1 managed?
A: Surgical procedures to decompress the posterior fossa vary in complexity and extent. Patients often experience immediate relief of limb paresthesia and tinnitus after surgical decompression of CM1. Most of the other symptoms are diminished or eliminated within several weeks to months. Asymptomatic patients, in whom CM1 may have been detected incidentally on imaging performed for various reasons, do not require surgery if there is no syrinx. The management of asymptomatic CM1 in patients with a syrinx is controversial. Guidelines suggest close follow-up of such patients, with surgery recommended if the syrinx expands or associated symptoms appear. Patients with a syrinx who have undergone decompression may have abatement of associated symptoms, and regression of the syrinx occurs in approximately 78% of patients. It is not clear why some patients, despite having undergone proper decompression, do not have decreases in syrinx-related symptoms or improvements in the findings on imaging studies.