Final answer:
A softened, spring-like area in an infant's skull could signify a serious medical condition. Diagnosis requires a healthcare professional's evaluation and may necessitate imaging studies to determine the underlying cause.
Step-by-step explanation:
The symptoms described and the finding of a softened spring-like region in the left parietal bone of an infant that gives the sensation of a ping pong ball when depressed and then released could be indicative of a serious medical condition. This type of physical finding in an infant typically represents an area of the skull where the bone might be thinner or not fully developed, and can occur due to various medical reasons such as a skull fracture, localized infection, or other conditions affecting the integrity of the skull. In severe cases, this might be associated with underlying brain abnormalities or trauma. Clinical evaluation by a healthcare professional, potentially including imaging studies like cranial ultrasound, MRI, or CT scan, would be critical to accurately diagnose the cause of this finding.