Banana sign on USG is seen in :
**Core Concept**
The "banana sign" on ultrasound (USG) is a characteristic appearance of a fetal cerebellum in the second trimester, which resembles a banana. This sign is significant in fetal medicine as it can indicate normal fetal development. The cerebellum's curvature and position are crucial in this context.
**Why the Correct Answer is Right**
The banana sign is seen when the cerebellum is in the correct position, with its curvature and the pons forming a smooth, continuous curve. This is often observed in the second trimester, particularly between 13-15 weeks of gestation. The cerebellum's normal development and positioning are essential for this sign to appear. The cerebellum's curvature is a result of the normal anatomy of the posterior fossa, where the cerebellum, brainstem, and cerebellar cisterns are located.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the "banana sign" is specific to the cerebellum's curvature and position, not to other fetal structures like the spine or limbs.
* **Option B:** This option is incorrect because the "banana sign" is not indicative of any specific fetal anomaly or pathology, but rather a normal anatomical feature.
* **Option C:** This option is incorrect because the "banana sign" is not related to any particular fetal movement or activity, but rather a static imaging finding.
**Clinical Pearl / High-Yield Fact**
The banana sign is often seen in combination with other normal fetal features, such as the "lemon sign" (a flattening of the frontal bones) and the "sagittal sign" (a straightening of the sagittal suture). These signs together can provide reassurance about fetal development and can be used in the assessment of fetal anatomy.
**Correct Answer: C**