**Core Concept**
In Down's syndrome, there's an association with abnormal head shape due to altered craniofacial development. This condition is characterized by an extra copy of chromosome 21, leading to various physical and developmental anomalies.

**Why the Correct Answer is Right**
The characteristic head shape in Down's syndrome is brachycephaly, which is a condition where the head is shorter from front to back compared to its width. This is due to the premature closure of the coronal suture, a fibrous joint that connects the frontal and parietal bones of the skull. As a result, the head appears short and broad. The brachycephalic head shape is a common feature in individuals with Down's syndrome.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it doesn't accurately describe the head shape associated with Down's syndrome. The term "dolichocephaly" refers to a long, narrow head shape, which is not characteristic of Down's syndrome.
**Option B:** This option is incorrect because it doesn't accurately describe the head shape associated with Down's syndrome. The term "macrocephaly" refers to an abnormally large head size, which is not characteristic of Down's syndrome.
**Option C:** This option is incorrect because it doesn't accurately describe the head shape associated with Down's syndrome. The term "microcephaly" refers to an abnormally small head size, which is not characteristic of Down's syndrome.

**Clinical Pearl / High-Yield Fact**
The characteristic brachycephalic head shape in Down's syndrome is often accompanied by other physical features such as a flat face, small ears, and a short neck. These physical features can be used to make a clinical diagnosis of Down's syndrome.

**Correct Answer:** C. Brachycephaly