Embryology USMLE Step 1 Practice Question
A 2-month-old male presents with a firm, non-tender midline sacrococcygeal mass noted on routine physical examination. The mass is located just superior to the coccyx. Imaging shows a well-circumscribed tumor containing mature bone, cartilage, adipose tissue, and disorganized neural elements. Genetic testing reveals a TP53 mutation. Which of the following embryologic abnormalities best accounts for this finding?
Answer choices
- AFailure of fusion of the neural folds during primary neurulation
- BIncomplete regression of the primitive streak and caudal eminenceCorrect answer
- CAbnormal migration of pluripotent neural crest cells to the midline
- DPersistence of the neurenteric canal connecting notochord to endoderm
- EFailure of notochord involution with ectopic notochordal remnants
- FIncomplete obliteration of the allantois with urachal remnant formation
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