Fig. 6.1
Normal T1 sagittal MRI of a 5-year-old
6.2.1 Developmental Anomaly
CM-I is anatomically the simplest of the Chiari malformations. Magnetic resonance imaging demonstrates descent of the cerebellar tonsils 5 mm or more below the foramen magnum and occasionally below the second cervical (C2) level (Figs. 6.2 and 6.3). Cerebellar tonsils that enter the cervical canal but descend less than 5 mm are considered cerebellar ectopia, not meeting the criteria for the diagnosis of Chiari malformation.
Fig. 6.2
Chiari I
Fig. 6.3
Chiari I
Skull-based deformities, such as a small posterior fossa and steep incline of the tentorium, may be present. Basilar impression or invagination, concavity of the clivus, and atlantoaxial assimilation have been associated with CM-I (Weprin and Oakes 2001). Although this historically was considered a condition of adulthood, CM-Is have been identified in all age groups, including the neonatal population (Lazareff et al. 2002; Menezes 1995; Nohria and Oakes 1991; Yundt et al. 1996).
The prevalence of hydrocephalus associated with CM-I is approximately 10% and may be caused by fibrous adhesions or scarring that develop between the dura, the arachnoid, and the cerebellar tonsils (Nohria and Oakes 1991). This in turn may cause obstruction of the flow of CSF from the fourth ventricle.
6.2.2 Acquired Anomaly
CM-I may develop in patients treated for hydrocephalus or pseudotumor with a ventriculoperitoneal shunt or lumboperitoneal shunt (Payner et al. 1994; Weprin and Oakes 2001). Chronic shunting of CSF from the lumbar subarachnoid space to the peritoneal cavity may cause the cerebellar tonsils to move caudally below the foramen magnum. This descent of the cerebellar tonsils may be reversed by removing the shunt. In patients with ventriculoperitoneal shunts, it has been reported that the overdrainage of the ventricles caused increased CSF in the subarachnoid space, theoretically changing the pressure gradient and contributing to the downward movement of the cerebellar tonsils. Other authors report that, with specific patients and techniques to prevent overshunting, this phenomenon can be avoided (Rekate and Wallace 2003).
6.3 Chiari II Malformation
The Chiari II malformation is present in nearly all children with myelomeningocele (MM) (Dias 1999). CM-II is probably a primary dysgenesis of the brainstem associated with the neural tube defect and multiple other developmental anomalies present in these patients (Greenberg 2010). However, there is evidence that patients undergoing intrauterine repair of the MM may not have the typical low-lying tonsils of the CM-II (Adzick et al. 2011; Sutton et al. 1999; Tulipan et al. 1998, 1999), thus placing into question the theory that this is a primary dysgenesis and giving support to the hydrodynamic theories of Chiari malformations. Indeed, the Management of Myelomeningocele Study (MOMS) (Adzick et al. 2011) demonstrated that 36% of the prenatal surgery group had no evidence of hindbrain herniation at the age of 12 months compared to 4% of the postnatal surgery group. Up to 90% of MM patients also develop symptomatic hydrocephalus, with 50% of infants showing evidence of hydrocephalus at birth (Detwiler et al. 1999). In the MOMS study, fewer CSF shunts were placed in infants in the prenatal surgery group by 12 months (40%) compared to the postnatal group (82%) (p < 0.001) (Adzick et al. 2011).
For these patients, the Chiari malformation appears to be more than hindbrain herniation but also includes anatomic changes in the supratentorial structures and the skull as well. The posterior fossa abnormalities include caudal descent of the pons, medulla, cerebellar vermis and fourth ventricle, “kinking” of the brainstem, “beaking” of the tectum, and aqueductal stenosis (Fig. 6.4). Some associated anomalies of the cerebral hemispheres include polymicrogyria, cortical heterotopias, dysgenesis of the corpus callosum, and a large massa intermedia. Skull deformities include “luckenschadel” or craniolacunia, shortening of bony clivus, and enlargement of the foreman magnum (Greenberg 2010). Hindbrain and lower cranial nerve dysfunction is the leading cause of death in children with myelodysplasia (Oakes et al. 2011).
Fig. 6.4
Chiari II
6.4 Chiari III Malformation
The Chiari III malformation involves descent of most of the cerebellum and brainstem below the foramen magnum and may be associated with a cervical or occipital encephalocele. The encephalocele may contain cerebellum, occipital lobes, and brainstem. Herniation of the fourth and lateral ventricles may occur. Hydrocephalus is often present (Oakes et al. 2011; Weprin and Oakes 2001).
6.4.1 Etiology
Despite being identified in the 1800s, a debate still continues about the cause of Chiari malformations. Although these malformations have abnormalities of the cerebellum and the craniocervical junction in common, they are thought to be distinct conditions with differing etiologic factors (Greenberg 2010; Strayer 2001). Many theories about the etiology have been proposed. Ongoing research brings hope for information that will help in determining best treatment options for this challenging spectrum of disorders (Table 6.1).
Theory | Mechanism |
|---|---|
Hydrodynamic | Hydrocephalus the primary cause |
Mechanical | (a) Spinal cord tethering causing abnormal development |
(b) Abnormal bony structures not providing enough space in the posterior fossa (cephalocranial disproportion) | |
Variation in pressure gradient | Pressure gradient between the intracranial and spinal compartments forcing the cerebellar tonsils to migrate caudally (craniospinal pressure gradient) |
Traumatic birth | Birth trauma causing tonsillar edema and arachnoid scarring |
6.4.2 Syringomyelia
Syringomyelia (or syrinx) refers to a cavitation or cyst within the substance of the spinal cord extending over many spinal levels (Figs. 6.5 and 6.6). Hydromyelia is a term that describes a distended central canal lined by ependymal tissue. The technical difference between these two terms has little clinical significance because the hydrodynamics of both types of cavitations are identical as evaluated by MRI. Therefore, medical literature currently uses the term syringomyelia to describe all intramedullary cysts with cerebrospinal fluidlike content (Oakes et al. 2011).
Fig. 6.5
T1 sagittal MRI showing cervical syrinx
Fig. 6.6
T1 sagittal MRI showing cervical and thoracic syrinx
Although syringomyelia most often occurs in association with a posterior fossa abnormality, a syrinx can also be associated with tumors, injury, and inflammatory processes or may simply be idiopathic.
Syringomyelia is present in 30–85% of patients with Chiari I malformation (Schijman 2004) and is found most often in the older female child who has a larger degree of tonsillar descent with CSF flow impairment (Strahle et al. 2011). Oftentimes the syrinx is found in the cervical spine (Strahle et al. 2011).
The medical literature has posed a variety of mechanisms for the development of the syrinx in patients with Chiari malformations. In general, there is agreement that the abnormal CSF dynamic associated with Chiari malformations produces a net bulk flow of CSF into the central canal (rather than a balanced bidirectional flow through the parenchyma) that creates the syrinx. The presence of syringomyelia will have an impact on symptom presentation, treatment options, and long-term outcomes (Dias 1999; Oakes et al. 2011; Weprin and Oakes 2001). Also, it is important to realize that a new syrinx in patients with CM-II with a ventriculoperitoneal shunt may represent a shunt malfunction causing altered spinal cord CSF dynamics.
Presyrinx, first described in 1999, is a reversible state of spinal cord edema caused by alterations in CSF flow, typically in the cervical region. Ongoing clinical examination and serial MRI imaging are used to monitor progression. The presyrinx may advance to a syrinx if untreated (Goh et al. 2008; Khoury 2015).
6.5 Presentation
6.5.1 Chiari I Malformation
Before the use of MRI, Chiari I malformations were thought to be a condition that is presented in late childhood or adolescence. Occipital and upper cervical headache is the most common presenting symptom in this age group, occurring in 63–69% of patients (Dias 1999; Hida et al. 1995). The headache may be triggered or exacerbated by Valsalva maneuver, extreme neck movement, or during exertional activities such as sports. Headaches may progress over time and, primarily in younger children, may cause nighttime awakening. Weakness or numbness of one or both arms may be present. Some patients report gait unsteadiness, sensory changes, and dysphagia.
On physical exam, nystagmus, facial hyperesthesia, dysarthria, palatal weakness, or tongue atrophy may be present. Vocal cord paralysis may be present in rare cases. Other possible findings include hyperactive upper extremity reflexes, positive Babinski, weakness of the upper and lower extremities, scoliosis, spasticity, and ataxia (Oakes et al. 2011; Weprin and Oakes 2001). The literature indicates, however, that 10% of all patients with CM-I present with headache only and have a normal neurological examination. This percentage may be higher in the pediatric population. A recent study reported findings of about 130 children with CM-I, of whom 21% presented with headache only and a normal neurological examination (Yeh et al. 2006). Diagnoses of CM-I in children and adolescents are often based on history, symptoms, and radiographic studies, in the absence of focal neurological findings.
In rare cases, ventral brainstem compression (VBSC) can occur when there is compression on the brainstem and upper spinal cord (Fig. 6.7). These patients will present with signs and symptoms similar to a CM-I such as neck pain and occipitalcervical headache. Other signs and symptoms include myelopathy or quadraparesis, brainstem dysfunction, lower cranial nerve abnormalities, basilar migranes, ataxia, facial pain, and nystagmus (Menezes 2008; Rider et al. 2015). Treatment for VBSC includes close observation as well as surgery. Two different surgical approaches, open transoral and endoscopic transnasal, may be performed depending on the size of the patient and their imaging studies.
Fig. 6.7
Sagittal MRI of 12-year-old boy showing ventral compression and Chiari I. He presented with new onset of progressive left-sided esotropia and blurry vision
The availability of MRI has assisted in the identification of Chiari malformations in the younger child. Infants and the nonverbal child may present with persistent crying and irritability as well as arching of the neck. Respiratory irregularities and recurrent aspirations may, in addition to the brainstem signs noted above, mark the presentation of the youngest patients (Benglis et al. 2011; Oakes et al. 2011). One recent study identified significant differences in the presentation of children 2 years and younger compared to those 3–5 years of age. The younger age group was more likely to present with oropharyngeal symptoms (77.8–38.1%, p = 0.01), while the 3- to 5-year-old subjects were more likely to present with scoliosis (38.1–16.7%, p = 0.03) or with syrinx (85.7–27.8%, p = 0.002). Although more of their older subjects (3- to 5-year-olds) presented with headache, this difference was not statistically significant (Albert et al. 2010) (Table 6.2).
Table 6.2
Categories of patients with Chiari I malformation based on predominant clinical symptoms
Headache | 98% | Arm pain | 27% |
Dizziness | 84% | Adbdominal pain | 23% |
Difficulty sleeping | 72% | Photophobia | 21% |
Wekanes of an upper extremity | 69% | Decrease or loss of hearing | 16% |
Neck pain | 67% | Tachycardia | 16% |
Numbness/tingling of an upper extremity | 62% | Fever | 15% |
Fatigue | 59% | Word-finding problmes | 14% |
Nausea | 58% | Vision loss | 7.2% |
Shortness of breath | 57% | Blackout spells | 6.8% |
Blurred vision | 57% | Apnea | 5.7% |
Tinnitius | 56% | Vertigo | 5.6% |
Difficulty swallowing | 54% | Peripheral vision loss | 5% |
Weakness of a lower extremity | 52% | Nystabmus | 5% |
Depression | 47% | Earache | 4.5% |
Vomiting | 15% | Epistaxis | 3.8% |
Diplopia | 15% | Increased snoring | 3.7% |
Generalized body weakness | 46% | Thoracic pain | 2.6% |
Disequilibrium | 46% | Hypotension | 1.9% |
Memory problems | 45% | Wakes up choking | 1.9% |
Numbness/tingling of a lower extremity | 43% | Leg pain | 1.7% |
Hoarseness in voice | 41% | Palpitations | 1.5% |
Chest pain | 39% | Hypertension | 1.5% |
Numbness in the face | 32% | Absent gag | 1.1% |
Anxiety | 30% | Face pain/tingling | 0.3% |
Slurred speech | 28% |
6.5.2 Chiari II Malformation
Chiari II malformations are present at birth in patients with an open neural tube defect. The literature reports that 18–33% of these patients will demonstrate Chiari II symptoms (Dias 1999; Weprin and Oakes 2001). The MOMS study provides evidence that prenatal repair of open neural tube defects may lessen the incidence of CM-IIs (Adzick et al. 2011). Infants with a symptomatic CM-II have a more rapid and severe onset of symptoms than those who present later in childhood. Symptom presentation early in life is related to higher morbidity and mortality.
Most patients are asymptomatic at birth, but a small group of neonates have respiratory distress. These patients demonstrate a poor respiratory drive, likely related to brainstem dysfunction. In infancy, respiratory distress including cyanotic spells, central or obstructive apnea, inspiratory stridor, and hoarse or high-pitched cries are the most common presenting signs. New or worsening stridor, accompanied by oxygen desaturation, in an infant with CM-II is considered a medical emergency.
Swallowing dysfunction is the second most common sign of a symptomatic CM-II (Dias 1999). Infants demonstrate poor suck and swallow coordination, nasal regurgitation, projectile emesis, choking, drooling, or pooling of food in the posterior pharynx. As a result, these children may suffer from failure to thrive, repeated episodes of aspiration pneumonia, and chronic gastroesophageal reflux. Nystagmus and vocal cord paralysis may also be present. This combination of symptoms reflects brainstem and lower cranial nerve dysfunction (Dias 1999; Weprin and Oakes 2001). Decreased upper extremity tone is another common sign in young children with a symptomatic CM-II.
The clinical presentation of a symptomatic CM-II in the older child is usually more gradual, with milder symptoms that are often responsive to surgical intervention. Symptoms in this age group include upper extremity weakness, spasticity, decreased function of the lower extremities, headache, neck pain, nystagmus, ataxia, and scoliosis. This group of symptoms is related to dysfunction of the cerebellum and spinal cord. Because these symptoms may progress very slowly, a complete history to identify subtle and gradual changes is vital. Presentation in adulthood is rare but would mimic the progression of symptoms of the older child (Table 6.3).
Table 6.3
Comparison of Chiari I and II malformations
Chiari I malformation | Chiari II malformation | |
|---|---|---|
Brain | Caudal descent of cerebellar tonsils > than 5–7 mm below foramen magnum | Caudal descent of cerebellar vermis, brainstem, and fourth ventricle below the foramen magnum |
Peg like or pointed | ||
Often asymmetric | ||
Common associated radiographic findings
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