20 Natural History and Management Options of Chiari 1 Malformation

Samuel Wreghitt, Bryden H. Dawes, and Augusto Gonzalvo

Abstract

This chapter explores the evidence related to the pathophysiology and management of Chiari malformation type 1 (CM-1). It reviews the natural history of both symptomatic and asymptomatic CM-1 patients and collates the available evidence to aid with management decisions. It examines the efficacy and complication rate of the various surgical techniques used to treat the condition.

Chiari malformation type 1 (CM-1) is a structural abnormality at the craniocervical junction, which involves the descent of the cerebellar tonsils through the foramen magnum affecting the dynamic flow of the cerebrospinal fluid (CSF). It is important to understand that normal craniocervical anatomy can include the cerebellar tonsils lying up to 3 to 5 mm below the rim of the foramen magnum in adults and up to 6 mm in infants.1

The presentation of patients with a CM-1 is variable and the indication for surgical management has always been controversial. While various Chiari malformations have been described, the focus of this chapter is on CM-1 (Fig. 20.1).

CM-1 presents in a variety of ways and, in most cases, symptoms start at the end of adolescence. They are generally related to raised intracranial pressure, cerebellar deficit, or associated spinal cord syrinx.

The most common presenting symptom in adults is an occipital headache worsened by coughing (cough headache) or Valsalva maneuvers, which typically last less than 5 minutes. However, many studies show that the type of headache can vary greatly, as shown in Table 20.1.² The International Headache Society has defined Chiari headaches under its own definition in an attempt to differentiate them from a primary cough headache—which is similar but generally can last longer (up to 2 h). Patients initially diagnosed with a primary cough headache require neuroimaging, as 40% of cases have an associated CM-1.³

Table 20.1 Types of headache associated with Chiari malformation type 1 (CM-1)

In addition, various other symptoms can be associated with a CM-1, as shown in Table 20.2.² Descent of the cerebellar tonsils can lead to central nystagmus, scanning speech, and truncal ataxia. Compression of the brainstem can present with hoarseness, dysarthria, palatal weakness, tongue atrophy, and sleep-related breathing disorders.

Table 20.2 Symptoms associated with Chiari malformation type 1 (CM-1)

20.1.1 CM-1-Associated Syringomyelia

CM-1 may be associated with syrinx in 30% of cases. The size of the CM-1-associated syringomyelia is noticeably wider (7–8 mm) in comparison to idiopathic forms of syringomyelia (3–4 mm). CM-1-associated syrinx is also more likely to have cranial extent into the cervical spine.⁴ It is also important to be aware that 25% of Charcot joints in the upper limbs are associated with syringomyelia.⁵

In contrast to type 2 malformations, there are generally no associated brain abnormalities to the cerebellar tonsillar descent. There are, however, a number of osseous abnormalities that include shortened clivus, underdeveloped posterior cranial fossa, basilar invagination, platybasia, pro-atlantal remnants, Klippel–Feil anomaly, atlantoaxial assimilation, odontoid retroflexion, and scoliosis.⁶

20.1.2 Pathophysiology of Chiari Malformation Type 1

CM-1 encompasses a heterogeneous and complex entity and may be idiopathic or acquired. Idiopathic CM-1 is associated with many congenital conditions. The abnormality results in crowding at the foramen magnum and impaction of the cerebellar tonsils. When compared with controls, patients with CM-1 have a smaller posterior fossa,^{7,​ 8,​ 9} shallow basiocciputs, and a disproportionate cerebellum-to-posterior fossa volume. In some cases, this correlates with the degree of cerebellar ectopia. It is proposed that this results from an underdevelopment of the occipital endochondrium during embryology.^{10,​ 11} However, this is not true for all patients with CM-1 and other factors are likely to contribute to the pathogenesis of the disease.

In addition to a reduced posterior fossa volume, patients with CM-1 have abnormal craniocervical junction CSF dynamics,¹² hyperdynamic motion of the craniocervical junction neural structures,^{13,​ 14,​ 15} and a reduced intracranial CSF compliance.

The pathophysiology of the cough headache typically associated with CM-1 is not known. Various mechanisms have been proposed, including compression of the upper cervical nerve roots by the descending tonsils,16^{,​ 17} transient craniospinal pressure dissociation,^{18,​ 19} strain of the cerebellar tonsils,¹³ increased CSF pressure,²⁰ and reduced CSF compliance of the posterior fossa.²¹ However, these theories fail to describe the spectrum of clinical and radiological presentation.

Similarly, the pathogenesis of CM-1-associated syringomyelia is not well understood. The classic theories include the hydrodynamic theory,²² the craniospinal dissociation theory,²³ and the ball valve (or ball-in-cone) theory.²⁴ Current theories propose that alternate CSF dynamics result in the transportation of fluid into the cord parenchyma via perivascular and extracellular spaces.²⁵

20.2 Selected Papers on the Natural History of Chiari Malformation Type 1

●Langridge B, Phillips E, Choi D. Chiari malformation type 1: a systematic review of natural history and conservative management. World Neurosurg 2017;104:213–219

●Killeen A, Roguski M, Chavez A, Heilman C, Hwang S. Non-operative outcomes in Chiari I malformation patients. J Clin Neurosci 2015;22(1):133–138

●Chavez A, Roguski M, Killeen A, Heilman C, Hwang S. Comparison of operative and non-operative outcomes based on surgical selection criteria for patients with Chiari I malformations. J Clin Neurosci 2014;21(12):2201–2206

20.3 Natural History of Chiari Malformation Type 1

Patients presenting with CM-1 normally fall into one of the following scenarios:

●Incidental CM-1 (with or without associated syrinx).

●New diagnosed symptomatic CM-1 and decision to manage conservatively.

●Clinical progression of a previously asymptomatic or minimally symptomatic CM-1.

Due to the fact that the general treatment of CM-1 is biased toward surgical management,²⁹ there are only few studies presenting its natural history. Therefore, the evidence to support decision-making is limited. The majority of studies into the natural history of CM-1 are based on a pediatric population, but the evidence presented here is targeted to the natural history of the adult population (Table 20.3).

Table 20.3 Studies included in qualitative synthesis

20.3.1 Asymptomatic Chiari Malformation Type 1

CM-1 is a relatively slowly progressing disease. For this reason, many patients with CM-1 are diagnosed as incidental findings. This is confirmed by the fact that the diagnosis of CM-1 is relatively common upon the reviewing of imaging. Morris et al³⁵ collated several magnetic resonance imaging (MRI) studies of normal adults to show diagnoses of CM-1 in 71 of 15,559 (0.24%) cases. In comparison, Meadows et al³⁶ reviewed consecutive imaging performed at a single institution, which showed diagnoses of CM-1 in 175 of 22,591 (0.8%) patients.

Two large studies in the pediatric population revealed the slow progression toward symptoms. Benglis et al37 managed 124 patients, ranging from 0.9 to 19.8 years (mean: 7 years), conservatively over approximately 3 years. On initial review, 43 were asymptomatic and 67 of the remaining 81 were deemed to have symptoms not related to their CM-1. Over this short period, none of the 124 patients had a progression of symptoms relating to their CM-1. Furthermore, in a larger study by Strahle et al³⁸ of 147 patients (mean: 7.7 years) over a longer follow-up of 4 years, 133 (90.5%) patients remained either asymptomatic or minimally symptomatic and not requiring surgical intervention.

An adult-based study by Nishizawa et al³³ followed 10 asymptomatic patients with incidentally identified syrinx associated with CM-1 for a period of 11 years. Only one patient required surgical intervention at the 7-year mark and, after surgical decompression, made a full recovery. Of note in this study is the fact that the imaging remained stable over the follow-up period. This selected evidence shows there is a benign nature to CM-1, with slow (if any) progression from either asymptomatic or minimally symptomatic patients.

Moriwaka et al^{21,​ 63} produced an epidemiological study in Japan of syringomyelia showing 1,243 cases, of which 684 (51.2%) related to CM-1. The follow-up of these 1,243 patients showed the clinical course was slowly progressive; 202 (17.9%) patients showed rather stable course including spontaneous resolution in 29 (2.3%) patients. These numbers include all pathologies with surgical and nonsurgical treatment but highlight that there is the option of a more conservative approach to managing the finding of a syrinx. In addition, there is also documented evidence of resolution of patients’ syrinx and their symptoms. Klekamp et al³¹ published a case report and literature review showing 10 patients (5 adults and 5 children) who experienced resolution of their CM-1-associated syrinx. Of the symptomatic patients, five showed improvement of their symptoms. This suggests that the common consensus of the presence of a syrinx associated with a CM-1 as a strong indication for surgical management is debatable.

20.3.2 Symptomatic Chiari Malformation Type 1

When providing medical advice to a patient with CM-1, it is imperative to know the natural history of this condition. Killeen et al²⁷ and Chavez et al²⁸ provide high-quality follow-up data of conservatively managed patients. Langridge et al have undertaken a detailed systematic review²⁶ that similarly shows, as in Table 20.4, the presenting symptoms of conservatively treated CM-1 patients.

Table 20.4 Presenting symptoms on diagnosis of CM-1

Related posts:

Natural History and Management Options for Cushing’s Disease Natural History and Management Options of Angionegative Subarachnoid Hemorrhage Natural History and Management Options of Ruptured Brain Arteriovenous Malformation Natural History and Management Options of Recurrent Glioblastoma Natural History and Management Options of Cerebral Metastases Natural History and Management Options of Unruptured Brain Arteriovenous Malformation

Stay updated, free articles. Join our Telegram channel

Join

Full access? Get Clinical Tree