noninvoluting

Noninvoluting is an adjective used in biology and medicine to describe something that does not undergo involution, meaning it does not regress, shrink, or return to a prior simpler form. Involution refers to the process by which tissues, organs, or lesions decrease in size or function after reaching a peak during development or after an active phase, such as the regression of many infantile hemangiomas. Therefore, noninvoluting describes structures or lesions that persist, grow, or remain stable rather than decrease.

In medical contexts, the term is often encountered in pediatric vascular anomalies. The noninvoluting congenital hemangioma (NICH) is a lesion present at birth that typically does not involute spontaneously and tends to persist or enlarge as the child grows. This contrasts with rapidly involuting congenital hemangiomas (RICH) and partially involuting lesions, which regress over time. NICH lesions are usually well-circumscribed, may be nodular or plaque-like, and can be complex if located over critical anatomy; they may ulcerate or bleed and can require intervention such as surgical excision, laser therapy, or embolization in selected cases. The terminology helps distinguish lesions by their natural history.

Beyond vascular lesions, noninvoluting can be used more generally to describe tissues that do not regress during maturation, aging, or post-inflammatory remodeling; however, the usage is most common in clinical descriptions of congenital vascular tumors.

Etymology: from Latin involutionem, “a rolling inward,” with the prefix non- indicating negation.

See also: involution, congenital hemangioma, infantile hemangioma, vascular anomaly.