Chiari I Malformation

Patients with Chiari I malformation are asymptomatic. The most common symptom, however, in both the adult and child, is pain or headache in the occipital/cervical region (neck pain) [24]. In the very young population, a history of headache or pain may be difficult to elicit, where these symptoms are more likely to manifest as excessive crying, irritability, and failure to thrive.[19][25]

It should be noted that the headache produced in Chiari I is often exacerbated with the Valsalva maneuver due to the reduced size of the foramen magnum. This should be differentiated from chronic headaches that do not vary with the Valsalva maneuver, which may be attributed to pathologies other than Chiari I, for example, intracranial hypertension.[26][27] Although migraine headaches have a prevalence similar to that of the general population, in individuals affected by Chiari I there is an earlier age of onset and a severe clinical presentation.[28]

Apart from headache and pain, a wide spectrum of clinical manifestations may characterize the malformation. In particular, signs and symptoms are mainly due to direct brainstem compression that may cause autonomic dysfunction.[29][30] Other signs, such as scoliosis, are structural. Clinical features may include[29][30][31][24][32][33][34]:

• Syncopal episodes and sinus bradycardia due to autonomic dysfunction
• Swallowing alterations and vomiting
• Balance difficulties with an unsteady gait 
• Problems in hand coordination
• Sensorial manifestations such as numbness and tingling, in the extremities 
• Dizziness
• Tinnitus
• Progressive muscular weakness in the arms and legs is seen, and stiffness in the back, shoulders, arms, or legs, represent clinical manifestations of syringomyelia. Acute paraparesis has been described as case reports. Syringobulbia can produce weakness in the facial muscles.
• Bladder and bowel problems can be the result of syrinx-induced compressive effects.
• Scoliosis, particularly in pediatric patients. Although scoliosis is due to syringomyelia, recent studies suggest that there is no association of syrinx length and holocord syrinx with scoliosis.
• Nystagmus may also manifest in Chiari I with syringobulbia; however, this is a less specific sign.

Adults and children may present with Chiari I differently. For example, pediatric patients are increasingly likely to present with brainstem dysfunction, sleep apnea, or feeding difficulty.[35] The latter is due to the involvement of the glossopharyngeal and vagus nerves resulting in an absent gag reflex and hoarseness.[36] As the cerebellum is involved in higher cognitive functions, potential cognitive alterations have been recently investigated, and the presence of a generalized cognitive impairment in the executive functioning, verbal fluency, spatial cognition, language, and memory processing, has been reported.[37]  

Neuroimaging

Magnetic resonance imaging (MRI) is the main investigation performed for Chiari type I malformation, providing a depiction of craniocervical junction anatomy with identification of secondary complications such as hydrocephalus or syringomyelia.[38]

When the patient is unable to undergo MRI scanning, other methods investigations to explore include CT myelography, non-contrast CT, and radiographs of the head and neck.

On MRI, as well as tonsillar descent, there may be an appearance of ‘peg-like’ or pointed tonsils, seen in both symptomatic and asymptomatic individuals.[39] Other associations include a cervicomedullary ‘kink,’ seen in up to 71% of symptomatic patients.[40] In general, the greater the degree of cerebellar tonsil descent, the greater the likelihood the patient is symptomatic.[18]  

Patients who have incidental tonsillar ectopia without symptoms may benefit from MRI cine CSF flow studies. Positive findings on CSF flow include pulsatile systolic tonsillar descent and CSF flow obstruction at the level of the foramen magnum. These findings can provide further information to help assess whether the patient may benefit from surgery.[41] 

Laboratory Studies

Laboratory studies are not used for the diagnosis of Chiari I. However, any preoperative workup requires appropriate baseline investigations including full blood counts, electrolytes and metabolites; alongside a chest radiograph and electrocardiogram (ECG). 

 Other useful tests may include:

• Sleep study: Involves sleeping overnight in a room where they can monitor breathing, snoring, oxygenation, and seizure activity to determine if there is any evidence of sleep apnea.

• Swallowing study: Fluoroscopy used to watch the internal swallowing process to determine if there is an abnormality suggestive of lower brainstem dysfunction. 

• Brainstem auditory evoked potential (BAER): It is an electrical test to examine the function of the hearing apparatus and brainstem connections. This is used to determine if the brainstem is working properly.

• Somatosensory evoked potentials (SSEP): An electrical test of the nerves involved in sensation, which gives some information about peripheral nerve, spinal cord, and brain function.

Prenatal diagnosis of Chiari type I malformation, and syringomyelia has also been described.[42]

Because there is no clear consensus about the precise algorithm for the management of Chiari type I malformation, its treatment remains rather empirical. It encompasses a combination of medical and surgical approaches through a multimodal dynamic strategy. 

Medical therapy

Medical management in Chiari I is limited and generally confined to symptomatology (e.g., headaches or neck pain). Non-steroidal anti-inflammatory drugs (NSAIDs), muscle relaxants, and physical support collars may provide symptomatic relief. However, these options provide little improvement of less common symptoms, for example, gait disturbance. Meditation, yoga, or mindfulness therapy have also been proposed for addressing pain.  

Surgical strategies

Surgical treatment is typically reserved for patients who present with severe or worsening symptoms who go on to have a confirmation of cerebellar descent on imaging and a Chiari malformation obstructing CSF flow confirmed by cine MRI. Surgery aims to provide decompression of the restricted cervicomedullary junction, allowing CSF flow to be restored to optimal levels. The main approach involves performing a suboccipital craniectomy at the level of the C1 posterior arch (C1/2 laminectomy), with or without associated duroplasty.[43] Thus, this intervention, indicated as posterior fossa decompression (PFD), is the most adopted neurosurgical approach focused on restoring CSF flow across the foramen magnum. The procedure is performed in up to 99% of the literature.[44] A minimally invasive procedure allowing resection of submeningeal cerebellar tonsillar herniation followed by reconstruction of Cisterna magna without craniectomy has been proposed for addressing Chiari I with syringomyelia.[45] Of note, cine MRI has been proposed for guiding the intraoperative decision to realize duraplasty during PFD.[46] Among non-invasive approaches, several methods have also been proposed to decompress syringomyelia with distal drainage to the subarachnoid space (syringosubarachnoid shunt).[47]

Important diagnoses to consider in the workup of Chiari I are:

• Incidental tonsillar ectopia (less than 5 mm)
• Chiari II to IV types
• Idiopathic intracranial hypertension (pseudotumor cerebri)
• Craniospinal hypotension
• Basilar invagination

Surgical outcomes are favorable, with 73% of patients improving less than 1-year postoperatively and 79% at 1 to 3 years at follow-up.[48] PFD induced symptom improvement in about two-thirds of individuals, especially in those without associated syringomyelia.[49]

The most common postoperative complications are CSF leakage and pseudomeningocele formation.[50][24] The latter may require revision surgery or shunt insertion.[51] Other complications include aseptic and bacterial meningitis, vertebral artery injury, and epidural hematoma formation.[52] Concerning the type of surgical approach, in a retrospective analysis, Farber et al. found that meningitis occurred especially in decompression and duraplasty performed using bovine pericardial xenograft compared with the allograft method.[53]

Postoperatively patients may experience headache and neck pain due to the operation. Neck exercises may be given to aid the return of full mobility as soon as it is able.

Patients typically return to work in 4 to 6 weeks, with a follow-up MRI performed at around 6 months to 1 year.

Full recovery from Chiari surgery may take months or longer. It is important to slowly increase activity in a graded manner, avoiding any strenuous lifting in the early phase of recovery.

While nothing can be done to prevent congenital Chiari type I malformation, patient education plays a large role in familiarising not only the patient about the signs and symptoms of the condition but also helping increase awareness of the close family, friends, and carers who may spend significant periods with the patient.

• The Chiari I malformation is the most common of the Chiari manifestations resulting in hindbrain abnormality. 
• While the genetics origin of the malformation requires more confirmation, the malformation can occur in several defined genetic syndromes.
• Many patients can be asymptomatic or paucisymptomatic, and the malformation is diagnosed more commonly in adolescents or adults.
• Patients may present with symptoms of occipital pain or chronic headache; however, they may also present with less specific symptoms such as swallow impairment or sleep apnea.
• MRI is the main investigation of choice in these individuals, allowing full visualization of the cervicomedullary junction. 
• Because algorithms for the management of the Chiari type I are not well-established, a combination of medical and surgical approaches through a multimodal dynamic strategy is mandatory.
• Surgical decompression is performed in symptomatic individuals with success, often significantly alleviating the patients presenting symptomatology and restoring full neurological function.

The Chiari type I malformation is a rare developmental disorder that is best managed by an interprofessional team that includes a neurologist, pediatrician, surgeon, social worker, nurse, and physical therapist. These patients tend to have many physical and functional limitations, including impairment of swallowing, speaking, and even walking.

While the prognosis for most patients is good, when clinically suspected, appropriate investigations should be performed promptly to facilitate an appropriate level of treatment (e.g.conservative vs. surgical) and, in turn, to prevent future deterioration.