**Question:** "Hour-glass" shape of the chest and "tri-radiate pelvis" are seen radiologically in -

A. Congenital Diaphragmatic Hernia (CDH)
B. Malrotation of intestines
C. Ankylosing Spondylitis
D. Osteogenesis Imperfecta

**Core Concept:**
The hourglass shape of the chest and tri-radiate pelvis are radiological findings in skeletal dysplasias, which are a group of over 400 genetic disorders characterized by disproportionate short stature, deformities, and abnormal bone growth. These findings help differentiate these conditions from other radiological abnormalities.

**Why the Correct Answer is Right:**
The correct answer is D. Osteogenesis Imperfecta, also known as brittle bone disease, is a genetic disorder characterized by defective collagen synthesis, leading to fragile bones that break easily. The radiological findings of hourglass chest and tri-radiate pelvis are due to the abnormal bone growth and shape changes in these patients.

**Why Each Wrong Option is Incorrect:**
A. Congenital Diaphragmatic Hernia (CDH) is a congenital defect in which abdominal organs herniate through a diaphragmatic defect. The radiological findings are not related to the hourglass chest and tri-radiate pelvis.

B. Malrotation of intestines is a condition where the intestines fail to rotate properly during fetal development. The radiological findings are not related to the hourglass chest and tri-radiate pelvis.

C. Ankylosing Spondylitis is a chronic inflammatory arthritis affecting the spine, sacroiliac joints, and other joints leading to deformities. The radiological findings are not specific to ankylosing spondylitis and can be present in other conditions as well.

**Clinical Pearl:**
Osteogenesis Imperfecta is a valuable differential diagnosis to keep in mind when evaluating patients with the hourglass chest and tri-radiate pelvis radiological findings. A thorough clinical examination and genetic testing are required to confirm the diagnosis.