WBR0563

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Embryology
Sub Category	SubCategory::Neurology
Prompt	[[Prompt::A 2-month-old boy is brought by his mother to the pediatrician's office for convulsions and irritability. On physical examination, the patient is found to have hydrocephalus and spina bifida. Following appropriate work-up, the physician informs the mother that the boy has a cystic dilatation of the 4th ventricle with enlargement of the posterior fossa. Which of the following errors in organ morphogenesis most likely affected this patient's cerebellar vermis?]]
Answer A	AnswerA::Absence of primordial tissue
Answer A Explanation	AnswerAExp::Agenesis is defined as the absence of primordial tissue. Dandy-Walker malformation is most commonly caused by the agenesis of the cerebellar vermis.
Answer B	AnswerB::Presence of primordial tissue but absence of cerebellar vermis
Answer B Explanation	AnswerBExp::Aplasia is defined as the presence of primordial tissue but absence of organ development.
Answer C	AnswerC::Presence of primordial tissue and incomplete development of cerebellar vermis
Answer C Explanation	AnswerCExp::Hypoplasia is defined as the presence of primordial tissue and incomplete tissue development.
Answer D	AnswerD::Presence of primordial tissue and presence of cerebellar vermis
Answer D Explanation	AnswerDExp::Normal development is defined as the presence of both the primordial tissue and organ development.
Answer E	AnswerE::Early development followed by regression of primordial tissue
Answer E Explanation	AnswerEExp::Agenesis is not characterized by the early development and regression of primordial tissue.
Right Answer	RightAnswer::A
Explanation	[[Explanation::Dandy-Walker malformation (DWM) is a heterogeneous group of disorders characterized by the triad: hydrocephalus, partial or complete absence of the cerebellar vermis, and posterior fossa cyst with enlargement of the 4th ventricle. DWM has multiple modes of transmission, including autosomal dominant, autosomal recessive, and X-linked recessive transmission. Although the disease may be isolated, it may be part of a malformation syndrome such as Meckel syndrome, Joubert syndrome, G syndrome, CDG syndrome, and Aicardi syndrome. DWM is also associated with congenital heart disease, cleft lip/palate, and classically, neural tube defects including spina bifida. In the vignette, the patient is most likely diagnosed with DWM with associated spina bifida. Patients with DWM usually present within the first year of life with neurological complaints, such as convulsions, or failure to meet developmental milestones. Dandy-Walker malformation is most commonly caused by the agenesis of the cerebellar vermis. Agenesis is defined as an error in organ morphogenesis that results in absence of both primordial tissue. Educational Objective: Dandy-Walker is characterized by agenesis of cerebellar vermis. Agenesis is defined as absence of organ due to absence of primordial tissue. References: First Aid 2014 page 445]]
Approved	Approved::No
Keyword	WBRKeyword::Organ, WBRKeyword::Morphogenesis, WBRKeyword::Agenesis, WBRKeyword::Aplasia, WBRKeyword::Hypoplasia, WBRKeyword::Development, WBRKeyword::Cerebellar, WBRKeyword::Vermis, WBRKeyword::Dandy, WBRKeyword::Walker, WBRKeyword::Syndrome, WBRKeyword::Dandy-Walker
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::