Slow-flow vascular malformations of the pons: capillary telangiectasias?

PURPOSE To report clinical and MR features that suggest telangiectatic vascular malformations of the pons:

METHODS The MR scans and clinical data of 12 patients demonstrating an enhancing pontine lesion with minimal or no signal abnormality on T2-weighted images were reviewed. None of the patients underwent angiography or biopsy. Follow-up scans, available for all patients between 3 weeks and 40 months (range, 11.5 months), were reviewed.

RESULTS The patients presented with a variety of symptoms including headache (n = 4), vertigo (n = 3), gait abnormality (n = 3), and hearing loss (n = 2). Two were referred for biopsy or treatment of presumed pontine glioma. On precontrast MR, 3 of 12 lesions were isointense on both T1- and T2-weighted images. Three of 12 lesions were slightly hypointense on T1-weighted images and 8 of 12 were slightly hyperintense on T2-weighted images. Postgadolinium images showed a discrete focus of enhancement with irregular or brushlike borders. Eight of 12 had an anomalous draining vessel from the lesion to the surface of the pons. None demonstrated mass effect or hemorrhage. Gradient-echo sequences in 7 patients all showed marked T2 shortening, despite the absence of hemorrhage on either T1- or T2-weighted images. None of the follow-up scans showed radiographic or clinical progression.

CONCLUSION The benign clinical course, lack of mass effect, and minimal or no T2 prolongation argue against neoplasm and instead indicate a vascular cause. We suspect the decreased signal on gradient-echo sequences represents elevated intravascular deoxyhemoglobin from stagnant blood flow. The findings are atypical for cavernous angioma or classic venous malformation. Although pathologic confirmation is lacking, the radiographic features are most consistent with capillary telangiectasia or a transitional capillary-venous malformation. Despite the absence of progression or hemorrhage in any of the patients to date, the long-term prognosis currently is unknown. We emphasize the importance of recognizing the nonneoplastic nature of these lesions.