WBR0563

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
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Sub Category
Prompt	[[Prompt::A 2 month old boy is brought by his parent to the physician'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 parents that the patient has a cystic enlargement of the 4th ventricle that is trapping the posterior fossa. Which of the following errors in organ morphogenesis most likely affected this patient's cerebellar vermis?]]
Answer A	AnswerA::Absent primordial tissue
Answer A Explanation	AnswerAExp::Agenesis is defined as the absence of primordial tissue. Agenesis of cerebellar vermis is observed in patients with Dandy-Walker syndrome.
Answer B	AnswerB::Present primordial tissue but absent cerebellar vermis
Answer B Explanation	AnswerBExp::Aplasia is defined as the presence of primordial tissue but absence of organ development.
Answer C	AnswerC::Present primordial tissue and incomplete development of cerebellar vermis
Answer C Explanation	AnswerCExp::Hypoplasia is defined as the presence of primordial tissue and incomplete development of cerebellar tissue.
Answer D	AnswerD::Present primordial tissue and present cerebellar vermis
Answer D Explanation	AnswerDExp::Normal development is defined as the presence of both the primordial tissue and cerebellar vermis.
Answer E	AnswerE::Early development followed by regression of of primordial tissue
Answer E Explanation	AnswerEExp::Agenesis is not characterized by the early development regression of primordial tissue.
Right Answer	RightAnswer::A
Explanation	[[Explanation::The patient is most likely diagnosed with Dandy-Walker syndrome, which is associated with hydrocephalus and spina bifida. Dandy-Walker syndrome is characterized by the cystic enlargement of the 4th ventricle that fills the posterior fossa. Most patients with Dandy-Walker syndrome are diagnosed within the first year of life. Patients usually present with neurological complaints, such as convulsions or failure to meet developmental milestones. Because Dandy-Walker syndrome is due to agenesis of the cerebellar vermis, the error in organ morphogenesis would be absence of both primordial tissue and organ. Educational Objective: Dandy-Walker is characterized by agenesis of cerebellar vermis. Agenesis is defined as absence of organ due to absence of primordial tissue. Educational Objective: References: ]]
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
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