## Core Concept
Caput succedaneum refers to a condition in newborns characterized by the swelling of the scalp due to the accumulation of fluid (edema) in the soft tissues, usually as a result of the pressure exerted during delivery. This condition involves the scalp's outer layers and can cross over suture lines.

## Why the Correct Answer is Right
The correct characterization of caput succedaneum includes features such as swelling that can cross suture lines, typically appears immediately after birth, and usually resolves on its own within a few days. The condition is a common, benign finding in newborns.

## Why Each Wrong Option is Incorrect
- **Option A:** Typically, caput succedaneum does not have a distinct boundary and can cross suture lines, which is a key characteristic. Therefore, if an option suggests it is confined by suture lines, it would be incorrect regarding caput succedaneum but actually aligns with another condition.
- **Option B:** If an option mentions that it appears immediately after birth and resolves quickly, it would be a correct characteristic of caput succedaneum.
- **Option C:** If an option notes it involves the scalp's outer layers and can cross suture lines, it accurately describes caput succedaneum.
- **Option D:** Without specific details on each option, we infer based on common characteristics of caput succedaneum.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that caput succedaneum is distinguished from cephalohematoma by its ability to cross suture lines and its immediate appearance post-birth. Cephalohematoma, in contrast, is confined by suture lines and may not be immediately apparent.

## Correct Answer: D. confined by suture lines.