Ring enhancement on CT after the removal of cerebral tumors

Ring enhancement at the operative site is occasionally seen on the CT scan after the total removal of brain tumors. The differentiation of the ring enhancement, seen as a normal postoperative phenomenon, from residual or early recurrent tumor and cerebral abscess can be difficult. We are presenting 9 cases of patients with meningioma and 20 cases of metastatic brain tumor, on whom serial postoperative CT was done. The results were as follows: 1) Postoperative ring enhancement does not necessarily represent a residual tumor and/or an early recurrence of the neoplasm. 2) Ring enhancement is seen as early as within one week postoperatively and is seen sequentially in the 2nd to 3rd postoperative week. 3) The former early enhancement often diminishes or disappears with steroid treatment, while the latter, late enhancement is not altered with steroid therapy. 4) Histological findings from 2 autopsy cases suggested that the former might be mainly due to a breakdown of blood brain barrier, and the latter, to capillary neovascularization. 5) As the ring will have disappeared in a few months, a patient with ring enhancement of over 3 months should be cautiously evaluated for residual or recurrent neoplasia and cerebral abscess. (author)