Chiari Malformation: A Never-ending Journey

Chiari malformation type I (CM1) is a common neurological disease consisting of a downward displacement of the cerebellar tonsils >5 mm below the foramen magnum (McRae lime).[1] After more than a century from the first description by Chiari,[2] the optimal management of this entity still represents one of the most discussed topics in neurosurgery, raising more questions than answers. The frequently observed discrepancy between the wide spectrum of clinical features and radiological picture along with the different surgical strategies explored to date, has represented an obstacle to providing shared and univocal guidelines.[3] Despite the remarkable effort made over the past decades and the numerous papers and clinical recommendations “flourished” in recent years, there is a paucity of “well-proven” therapeutic guidelines for this argument, both in the pediatric and adult populations. The exact cause of a congenital Chiari malformation type I is not known. A problem during fetal growth may cause the defect. It may be caused by contact with harmful substances during pregnancy. Or it may be linked with genetic problems that run in families. An acquired Chiari malformation type I happens to a person after birth. It is caused by excess leaking of spinal fluid from the lower back (lumbar) or chest (thoracic) areas of the spine. This can happen because of an injury, contact with harmful substances, or an infection. Chiari malformations are associated with the formation of a syrinx, a fluid-filled pocket, or cyst, in the spinal cord. This condition is also known as syringomyelia. As the cyst fills with cerebrospinal fluid, it expands, putting pressure on the spinal cord. In some patients with a Chiari malformation, increasing pressure from a syrinx can affect neuromuscular function, causing limb weakness or difficulties with walking or breathing. Some children will show signs of a spine syrinx, but others will not. In these situations, an MRI scan may be needed for a definite diagnosis. Scoliosis can be recognized in children younger than 16 whose spines are still growing; the presence of a syrinx can also be associated with the development of scoliosis, an abnormal, lateral curvature of the spine. Type 2 Chiari malformations can also be associated with hydrocephalus, a condition in which there is an obstruction of the flow of cerebrospinal fluid that is found inside the ventricles which are inside the brain. The buildup of fluid causes the pressure inside the head to increase and the child’s skull bones to expand to a larger-than-normal appearance. Sleep apnea is another problem that occurs in people with a Chiari malformation. This is a serious sleep disorder characterized by brief interruptions in breathing during sleep. A sleep study can confirm the presence of sleep apnea, so a doctor can prescribe treatment. Chiari malformation symptoms can also include: hoarseness, difficulty swallowing rapidly, nystagmus, muscle weakness, lack of balance or abnormal reflexes, and finally nerve problems, including paralysis.[3] Controversy exists in every management aspect, including indications, timing, and types of surgery. Moreover, the outcomes of patients treated for CM are frequently evaluated according to methods inconsistent and not comparable.[4] Does CM1 always represent a pathological entity or is it more correct to consider a spectrum ranging from paraphysiological entities to markedly pathological conditions? In some individuals, the configuration of the cerebellar tonsils and the foramen magnum might fall within a spectrum of normal variation rather than constituting an overt pathology. Several authors have associated CM1 with a reduction in posterior fossa volume as a result of an abnormal development of the occipital somite. On the other hand, some others have challenged the idea that a reduced posterior fossa volume is inherently pathological, showing an intrinsic variability in various measurements in the average and CM1 populations. Is CM1 essentially caused by instability at the craniovertebral junction? The association of CM1 with malformations of the cranial base and craniovertebral junction, characterized by variable degrees of instability,[5] is well-known. In recent years, the association between CM1 and instability of the craniovertebral junction has been at the center of a debate originating from a statement by Goel.[6] His theory, connecting basilar invagination, Chiari malformation, and syringomyelia, suggests that tonsillar herniation is a compensatory mechanism acting as a sort of protective response at the bulbomedullary junction from dynamic compression. Various authors such as Menezes have clearly illustrated the effective role of craniovertebral junction (CVJ) fixation in treating CM1 associated with CVJ instability or malformations.[7] However, Goel recognizes some form of CVJ instability in every CM1 patient, thus advocating for atlantoaxial fixation in all cases of CM with or without syringomyelia, regardless of the presence or absence of basilar invagination or other alterations in CVJ structure/mechanics.[8] Our group, in the wake of an experience matured both in laboratory[9,10] and clinical setting consisting in hundreds of cases involving CVJ[11,12] and thoracic[13] and lumbar spine, believes that not all cases of CM are due to atlantoaxial instability and that the indication for fixation should be evaluated on a case-by-case basis. Despite the efforts made by the scientific community in the form of personal experiences and consensus meetings in recent years, the CM chapter cannot yet be considered closed, both in terms of diagnosis and therapeutic options, and the debate remains open, with significant potential for future advancements and innovation.