Neurology Teaching! Chiari malformation edition

Welcome to Part 8 of neurology teaching! I am a neurology resident who loves teaching medical students, fellow residents, and my patients-- and one of my favorite ways to teach is using images.

I have had several folks request that I feature Chiari malformations as a topic, so here we go!

This is very common and usually incidentally found on imaging (type 1).

As usual I rely heavily on Radiopaedia.org, which is free to access and a wonderful resource for reviewing imaging.

Part 1: https://imgur.com/gallery/DTKTFU1 (intro)
Part 2: https://imgur.com/gallery/jzjpPoD (strokes)
Part 3: https://imgur.com/gallery/ANw2CDd (meningitis)
Part 4: https://imgur.com/gallery/Fsm9Buv (parasites)
Part 5: https://imgur.com/gallery/s8OvBL2 (intracranial pressure)
Part 6: https://imgur.com/gallery/Xksvovi (pupils)
Part 7: https://imgur.com/gallery/eahHOpS (multiple sclerosis)

Before we get started, let's review some anatomy!

Above is a T1 weighted MRI image, in the sagittal plane. This demonstrates normal anatomy of the cerebellum and the skull space the cerebellum occupies: the posterior cranial fossa.

The structures we're going to focus on are indicated:
1. Cerebellum: the back part of the brain, responsible for balance and coordination of movement and posture (among other things). It has 2 hemispheres, a midline structure called a vermis, and part of its anatomy includes the tonsils.

2. Cerebellar tonsils: part of the cerebellum, called tonsils presumably due to their shape. They are the lowest-lying part of the cerebellum and it is displaced downward in Chiari malformations, as we will see.

3. The foramen magnum: this is the hole at the base of your skull where the brainstem leaves the skull and becomes the spinal cord. On imaging there is a reference line corresponding to this place as above. In Chiari malformations, the cerebellum and sometimes parts of the brainstem are displaced downward through the foramen magnum.

Type 1 Chiari malformations are characterized by abnormally shaped (peg-like) and low-lying cerebellar tonsils which extend at least 5mm through the foramen magnum.
You can see in the above pictures the cerebellar tonsils squishing through the foramen magnum.
Most affected people are discovered incidentally to have this, and never have significant symptoms.

Symptoms, when present, include:
1. Headaches: typically present in teens/adults, located in back of head/neck. Classically they are brought on or substantially worsened by coughing or bearing down.

2. Symptoms of brainstem compression: slurred speech, difficulty swallowing, tongue weakness, eye movement abnormalities, recurrent aspiration, central sleep apnea, spasticity, weakness, bowel/bladder dysfunction.

3. Symptoms of cerebellar involvement: ataxia, incoordination, eye movement abnormalities, vertigo

4. Syringomyelia (see below)

Chiari type 1 is associated in a minority of cases with a malformation of the spinal cord, called syringomyelia or syrinx (this is a great scrabble word BTW). This may be asymptomatic or can cause symptoms.

Syrinx is when a fluid-filled cavity/cyst forms in the spinal cord. This is usually due to disrupted CSF flow, which can occur in Chiari malformations. A small syrinx is seen on the first image of this post. On these 2 images you can see the gray spinal cord interrupted by extensive syringomyelia. While the first image of this post may be asymptomatic given its size, the 2 above are most likely symptomatic given the degree of spinal cord disruption.

The symptoms of syrinx are related to the structures of the spinal cord involved, but most likely people have weakness and spasticity of the proximal muscles (shoulders, hips) and incoordination.

Excuse the painful formatting of this one.

Chiari 2 is less common, and essentially always detected at birth or in utero. It is associated with more visible abnormalities that we'll discuss later.

The brain abnormalities characteristic of Chiari II are downward displacement of the cerebellar vermis, tonsils, medulla oblongata and often consequently the 4th ventricle through the foramen magnum.

You can already see this is likely to be more severe than Chiari I malformations.

Due to this abnormal displacement of structures, affected individuals commonly experience hydrocephalus, or CSF buildup, which can be seen in the images above.

Symptoms of Chiari type II vary extensively. They may include difficulty swallowing, weakness, difficulty breathing, apneic spells, aspiration. When associated with other brain abnormalities or severe hydrocephalus there can be intellectual or developmental abnormalities and delays.

There are some individuals with Chiari type 2 that are of normal intelligence and are independent.

The main reason that Chiari II is diagnosed early in life is because of the visible abnormality associated with it: Myelomeningocele (my-elo-men-in-go-seel).

Myelomeningocele is disrupted or abnormal spinal cord and spine development, where a part of the spine (bones) do not fuse correctly. This is a severe type of spina bifida. It results in protrusion of the spinal cord, nerves, CSF out of the spinal canal, into a pocket that lies beneath the skin. This causes damage to the affected part of the spinal cord, and often paralysis and lack of sensation below the level of the lesion.

Above, you see 2 examples of myelomeningocele (literally means outpouching of spinal cord and meninges). On the left the more common type, where the very bottom of the spine fails to close and the nerves protrude through the outpouching. On the right you see a cervical myelomeningocele where there is extensive disruption of the cervical part of the spinal cord. You can also see this poor infant is affected with severe hydrocephalus as a consequence of their malformations.

Chiari III is much rarer than the others. This is a combination of things including displacement of the medulla and a high cervical or occipital encephalocele (outpouching of brain) that usually contains much of the cerebellum and an may contain other brain parts. It can co-occur with any features of Chiari I or II.

There is a very high mortality rate associated with this abnormality, usually due to respiratory failure as an infant. Survivors have severe impairments.

For Chiari I or II, foramen magnum decompression can be considered for severe symptoms. This is not a minor surgery, and there are risks. Major props to my neurosurgery colleagues and their skills in this arena.

Thanks for reading along and letting me share my love of neurology with all of you!