Patients with congenital vascular malformations often suffer from an impaired quality of life because of pain and functional disabilities. Sirolimus is an effective treatment; however, it can lead to serious adverse events.

This case series aims to address whether low target sirolimus levels will result in a high efficacy in patients with therapy-resistant low-flow malformations and will lead to a low incidence of serious adverse events?

An improvement in symptoms was seen in 85% of patients, a rate which is comparable to those found in the literature, and related to less serious adverse events. However, menstrual cycle disturbances were seen as a new observed adverse event.

This case series suggests that low dose sirolimus is a high efficacy and safe treatment of patients with vascular malformation. Future research is necessary to confirm this result, since lifelong treatment is likely required for patients with low-flow vascular malformation.