## Why "Lymphedema and subsequent fibrosis/scarring of the nuchal region during fetal development" is right The webbed neck (pterygium colli) in Turner syndrome results from embryologic lymphedema of the nuchal region that undergoes fibrosis and scarring during fetal development. This is a pathognomonic feature of 45,XO karyotype and reflects the characteristic lymphatic dysplasia seen in Turner syndrome. The clinical presentation of short stature, primary amenorrhea, and the characteristic karyotype 45,XO confirms the diagnosis, and the webbed neck is a direct consequence of this embryologic lymphatic abnormality (Nelson 21e Ch 619; Harrison 21e Ch 388). ## Why each distractor is wrong - **Failure of neural crest cell migration to the neck region**: While neural crest cells do contribute to neck structures, the webbed neck in Turner syndrome is specifically due to lymphedema, not neural crest migration failure. This would cause different congenital anomalies (e.g., DiGeorge syndrome). - **Defective collagen synthesis due to vitamin C deficiency**: Vitamin C deficiency causes scurvy with defective collagen, but this is not the mechanism of webbed neck in Turner syndrome. Turner syndrome is a chromosomal disorder, not a nutritional deficiency. - **Abnormal development of the sternocleidomastoid muscle**: While muscular abnormalities can affect neck appearance, the webbed neck in Turner syndrome is specifically a result of lymphedema scarring, not primary muscle dysplasia. **High-Yield:** Pterygium colli (webbed neck) in Turner syndrome = fetal lymphedema → fibrosis; always screen for coarctation of aorta (30% incidence) and horseshoe kidney (50%) in confirmed Turner syndrome. [cite: Nelson 21e Ch 619; Harrison 21e Ch 388]
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