It needs to be determined by the timing of the bleeding. If a blood vessel ruptures relatively large after the injury and a hematoma forms immediately, it is called a primary hematoma. A delayed hematoma is a hematoma that is not detected on examination at the time of the injury, but is detected after a delay of some time, which may be hours, days or even months. There is a time delay from the primary injury, so it is called a delayed hematoma. This delayed hematoma can be a challenge for the physician. When a patient is first injured, the vascular damage may not be significant enough to detect a hematoma in the skull when a CT scan is done. If the doctor doesn’t pay attention to it, doesn’t keep it under observation, or even doesn’t monitor the vital signs, after some time, the hematoma will form and compress the brain tissue, producing secondary symptoms, damage, or even forming a brain hernia, which is life-threatening. Therefore, late-onset hematoma is hidden, confusing, and easy to cause misdiagnosis or even missed diagnosis, patients, family members and medical staff should be vigilant, close observation, early detection and early treatment.