NQ-045 Answer: (A) Chiari I malformation.

Pathology of the case: In this case, the tonsil (black arrow) is herniated into the upper cervical cord. There is no obvious deformation of the pons and brain stem. The cerebellar vermis (white arrow) does not appear to be malformed. These findings are that of a Chiari I malfromation.

Chiari II malformation is characterized by displacement of the cerebellar vermis combined with deformities of the medulla and tectal plate with the later one leading to the tectum adopting the shape of a bird’s beak (so-called “beaking of the tectum”). It is often associated with syringomyelia, hydromyelia, spinal bifida, meningocele or meningomyelocele, and hydrocephalus. It can also associate with other malformations of the brain, cranium and meninges, cardiovascular, gastrointestinal and genitourinary systems. Chiari type II malformation is probably secondary to a neural tube defect. Chiar II malformations are typically associated neural tube defects such as meningomyelocele. The absence of a spinal defect in a case suspicious of Chiari II malformation should raise a concern of the correctness of the diagnosis.

Chiari III malformation refers to an encephalocele formed by herniation of the structures of the posterior fossa, including the cerebellum, through an occipitocervical or high cervical bony defect. There may also be beaking of of the tectum, elongation and kinging of the brain astem and lumbar spina bifida.

Dandy-Walker syndrome refers to a syndromic malformation of the cerebellum and posterior fossa. The three essential features include complete or partial agenesis of the vermis, cystic dilatation of the fourth ventricle and enlargement of the posterior fossa. Hydrocephalus is a frequent but inconstant finding. Other findings include elevation of the tentorium cerebelli and lateral, transverse sinuses and torcula (torcular Herophilli), and lack of patency of the foramina of Magendie and Luschka. Other cerebral and visceral anomalies are present. It is the presence or absence of other cerebral and visceral abnormalies that determines the prognosis of individuals. About 68% of all cases have other developmental abnormalities of the CNS. Facial abnormalities may also be seen.

Caudal regression syndrome also known as the mermaid syndrome comprises a variable defect of lumbar vertebrae, sacrum, and coccyx. This is a severe developmental field defect of the posterior axis caudal blastema. The severest form is sirenomelia (mermaid syndrome). It is frequently associated with abnormalities of the anorectal and urogenital systems and lower limbs. The entire urinary tract can be absent. The pathogenesis is probably related to the failure of growth of the caudal eminence. The strongest association of caudal regression is with maternal diabetes, it has also been related to deletion of chromosome 7q, autosomal dominant and, probably, autosomal recessive transmission. Timing: it occurs in the primitive streak stage during week 3 of gestation before development of the allantois, and the allantoic vessels are usually absent. There is a single umbilical artery that arises directly from the aorta.