A 3-year-old boy presents with disproportionate short stature (height at 5th centile, head circumference at 95th centile), frontal bossing, midface hypoplasia, rhizomelic limb shortening, trident hand, and lumbar lordosis. Skeletal survey confirms achondroplasia. The structure marked **A** in the diagram shows the characteristic pelvic appearance in this condition. Which of the following best describes the pathological anatomy of the structure marked **A**?
A. Narrowed pelvic inlet with prominent ischial spines and normal acetabular orientation
B. Symmetrical iliac wings with anterior pelvic tilt and increased acetabular depth
C. Squared iliac wings with horizontal acetabular roofs and narrow sacrosciatic notches
D. Flared iliac wings with vertically oriented acetabular roofs and widened sacrosciatic notches
Explanation
Why "Squared iliac wings with horizontal acetabular roofs and narrow sacrosciatic notches" is right
The structure marked A is the champagne-glass (or tombstone) pelvis—the pathognomonic skeletal hallmark of achondroplasia. This distinctive appearance is characterized by squared (not flared) iliac wings, horizontal (flat) acetabular roofs, and narrow sacrosciatic notches with a small pelvic inlet and outlet. This morphology results from the constitutive FGFR3 signaling that inhibits chondrocyte proliferation at the growth plate, affecting endochondral ossification throughout the skeleton, including the pelvis. Recognition of this pelvic anatomy on skeletal survey is critical for confirming the diagnosis of achondroplasia in a child presenting with disproportionate short stature.
Why each distractor is wrong
Flared iliac wings with vertically oriented acetabular roofs and widened sacrosciatic notches: This describes a normal or hyperlordotic pelvis, not the characteristic squared, horizontally oriented anatomy of achondroplasia. Flaring and widening are opposite to the pathological changes seen in achondroplasia.
Narrowed pelvic inlet with prominent ischial spines and increased acetabular depth: While pelvic inlet narrowing does occur in achondroplasia, prominent ischial spines and increased acetabular depth are not features of the champagne-glass pelvis. This describes features more consistent with other skeletal dysplasias or pelvic contracture.
Symmetrical iliac wings with anterior pelvic tilt and increased acetabular depth: Anterior pelvic tilt and increased acetabular depth are not characteristic of achondroplasia. The champagne-glass pelvis is defined by squared iliac wings and horizontal (flat) acetabular roofs, not increased depth.
High-YieldNEET PG
The champagne-glass pelvis (squared iliac wings, horizontal acetabular roofs, narrow sacrosciatic notches) is the pathognomonic skeletal finding in achondroplasia and results from FGFR3-mediated inhibition of chondrocyte proliferation.
Nelson Textbook of Pediatrics 21e — Achondroplasia section
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