The Perplexity Surrounding Chiari Malformations – Are We Any Wiser Now?

Abstract

Chiari malformations are a diverse group of abnormalities of the brain, craniovertebral junction, and the spine. Chiari 0, I, and 1.5 malformations, likely a spectrum of the same malformation with increasing severity, are due to the inadequacy of the para-axial mesoderm, which leads to insufficient development of occipital somites. Chiari II malformation is possibly due to nonclosure of the caudal end of the neuropore, with similar pathogenesis in the rostral end, which causes a Chiari III malformation. There have been significant developments in the understanding of this complex entity owing to insights into the pathogenesis and advancements in imaging modalities and neurosurgical techniques. This article aims to review the different types and pathophysiology of the Chiari malformations, along with a description of the various associated abnormalities. We also highlight the role of ante-and postnatal imaging, with a focus on the newer techniques in the presurgical evaluation, with a brief mention of the surgical procedures and the associated postsurgical complications. ABBREVIATION: CM ¼ Chiari malformation C hiari malformations (CMs) are a group of rhombencephalic abnormalities, initially described by Hans Chiari, traditionally classified into 4 types. 1-3 Types I to III are associated with a varying degree of caudal displacement of the contents of the posterior fossa, along with cerebellar tonsillar herniation through the foramen magnum. Type IV is characterized by cerebellar hypoplasia or aplasia and an occipital encephalocele. 1-3 Because of the complex nature of the associated abnormalities, CMs can present with diverse clinical manifestations, secondary to the involvement of the cerebellum, brain stem, spinal cord, lower cranial nerves, and altered CSF flow dynamics. Recent advances in imaging techniques, such as phase-contrast imaging, cine MR imaging, and DTI, with frequent imaging and surgical management of these

Chiari III malformation with defect in Liliequist membrane on MR imaging

“…Other than encephalocele, findings of Chiari II malformation are present in cases of Chiari III malformation including small posterior fossa and inferior herniation of cerebellum and brainstem. [1,4] Osseous malformations include occipital bone defects, dorsal scalloping of clivus and posterior petrous pyramids, posterior cervical agenesis, and segmentation anomalies of cervical spine. [5] Erol FS et al in 2011 reported a case of Chiari III malformation with Klippel Feil syndrome in a 4-year-old boy.…”

“…Other than encephalocele, findings of Chiari II malformation are present in cases of Chiari III malformation including small posterior fossa and inferior herniation of cerebellum and brainstem. [ 1 , 4 ]…”

New Association between Idiopathic Scoliosis and Luckenschadel Skull (Lacunar Skull)

“…This condition has been suggested to be a fetal developmental anomaly caused both by changes in intracranial pressure during pregnancy and developmental anomalies of the calvarium and internal periosteum [24]. A current theory suggests that the CM-II and the Luckenschadel skull reflect the absence of cerebral ventricular distension because of decompression of an open neural tube [25]. Such a lack of stretching inhibits the normal development of membranous plates of the fetal calvarium, creating abnormally irregular collections of collagen fibers that, when ossified, yield the radiographic findings of the Luckenschadel skull.…”

“…A current theory suggests that the CM-II and the Luckenschadel skull reflect the absence of cerebral ventricular distension because of decompression of an open neural tube [25]. Such a lack of stretching inhibits the normal development of membranous plates of the fetal calvarium, creating abnormally irregular collections of collagen fibers that, when ossified, yield the radiographic findings of the Luckenschadel skull.…”

Acromegaly, Herniation of Cerebellar Tonsils, and Arnold–Chiari 1 Malformation: The Importance of Right Definitions

“…The Arnold–Chiari malformation is a congenital underdevelopment of the posterior cranial fossa that may lead to the displacement of the cerebellar tonsils in the magnum foramen, and it is divided into four types, with type 1 being the one with the minor protrusion of the cerebellar tonsils and often asymptomatic and the type 4 being the one with the major protrusion and more significant symptoms [ 1 ].…”