Cavernous malformations are rare sequelae of stereotactic radiosurgery for brain metastases.

The development of cavernous malformations many years following conventionally fractionated brain irradiation is well recognized and commonly reported. However, cavernous malformation induction following stereotactic radiosurgery (SRS) is largely unreported. Herein, we describe two cases of cavernous malformation formation years following SRS for brain metastases. A 20-year-old woman with breast cancer brain metastases received treatment with whole brain radiotherapy (WBRT), then salvage SRS 1.4 years later for progression of a previously treated metastasis. This lesion treated with SRS had hemorrhagic enlargement 3.0 years after SRS. Resection revealed a cavernous malformation. A 25-year-old woman had SRS for a brain metastasis from papillary thyroid carcinoma. Resection of a progressive, hemorrhagic lesion within the SRS field 2 years later revealed both recurrent carcinoma as well as cavernous malformation. As patients with brain metastases live longer following SRS, our cases highlight that the differential diagnosis of an enlarging enhancing lesion within a previous SRS field includes not only cerebral necrosis and tumor progression but also cavernous malformation induction.