Embryology USMLE Step 1 Practice Question
A 5-year-old boy is brought to the clinic by his parents for evaluation of constipation and a visible mass at the base of his spine. Physical examination reveals a firm, non-tender 4×5 cm sacrococcygeal mass. Vital signs are within normal limits. MRI shows a mixed-density lesion at the sacrococcygeal junction without spinal canal involvement. Histopathology demonstrates mature bone, striated muscle, cartilage, and ciliated respiratory epithelium. Which of the following embryologic abnormalities best explains the origin of this tumor?
Answer choices
- AFailure of primordial germ cells to complete migration from the dorsal mesentery to the gonadal ridge
- BIncomplete regression and migration of the tail bud and caudal epiblast during weeks 4-8 of developmentCorrect answer
- CAberrant lateral plate mesoderm differentiation during somitogenesis
- DFailed delamination of neural crest cells from the neural tube
- EAbnormal endoderm invagination at the primitive pit during gastrulation
- FDefective notochord formation during primary neurulation
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