Juxtacortical means a lesion lies next to the cortex, such as just beneath the outer layer of bone or brain depending on the context.
This is mainly a scan description, not a symptom. Any symptoms depend on what the lesion actually is and where it is located.
Imaging helps because the exact position of a lesion next to the cortex can narrow the list of likely causes and guide whether more tests, follow-up scans, or biopsy are needed.
The location helps radiologists narrow the list of likely causes when interpreting the scan.
Management depends entirely on the organ involved and the rest of the imaging appearance.
This entry explains the word. If it appeared on your report, the next step is getting that report interpreted for your case.