What is an Interval Hemorrhage?
An interval hemorrhage refers to bleeding that develops or becomes apparent on repeat imaging after an initial scan showed either no hemorrhage or a smaller hemorrhage, occurring during the time interval between the two imaging studies.
Clinical Context and Definition
The term "interval hemorrhage" is used across multiple medical contexts to describe hemorrhage that appears or expands between sequential imaging studies. This concept is particularly important in several clinical scenarios:
Traumatic Brain Injury Context
In traumatic intracranial hemorrhage (tICH), interval hemorrhage specifically refers to bleeding that appears in areas of the brain that were normal or nearly normal on the initial CT scan taken shortly after injury 1. This delayed hemorrhage typically manifests within 48 hours of head trauma, though it can occur later 1.
The incidence of progression after an initially stable repeat scan is remarkably low (1.9%) when the first interval head CT at approximately 6 hours shows stability 2. Among patients with repeat imaging, approximately 25.7% experience some progression, but 94.4% of these progressions are detected on the initial 6-hour interval scan 2.
Key Pathophysiologic Mechanisms
The development of interval hemorrhage involves several mechanisms 1:
- Coagulation abnormalities that develop or worsen over time
- Necrosis of blood vessels in areas of brain injury
- Dysautoregulation of cerebral blood flow
- Release of tamponade effect following evacuation of extra-axial hematomas
Postpartum Context
In obstetric medicine, the term relates to the timing classification of postpartum hemorrhage (PPH). Primary or early PPH occurs within the first 24 hours after delivery, while late or delayed PPH occurs between 24 hours and 6 weeks postpartum 3. The "interval" here refers to the time period after delivery when hemorrhage develops.
Clinical Significance
Interval hemorrhage carries significant prognostic implications, with mortality rates of 50% or higher reported in traumatic cases 1. The detection of interval hemorrhage requires:
- Serial imaging protocols with appropriate timing
- Clinical vigilance for neurologic deterioration
- Risk stratification based on initial injury severity and patient factors
Common Pitfall
A critical pitfall is assuming that a single stable repeat scan guarantees no further bleeding risk. However, the data show that after demonstrating stability on the first interval scan, the risk of subsequent expansion drops dramatically to less than 2% 2, supporting earlier ICU discharge in appropriate patients.