Atypical MRI features in soft-tissue arteriovenous malformation: a novel imaging appearance with radiologic-pathologic correlation.

BACKGROUND: The absence of a discrete mass, surrounding signal abnormality and solid enhancement are imaging features that have traditionally been used to differentiate soft-tissue arteriovenous malformations from vascular tumors on MRI. We have observed that these findings are not uncommon in arteriovenous malformations, which may lead to misdiagnosis or inappropriate treatment.

OBJECTIVE: To estimate the frequency of atypical MRI features in soft-tissue arteriovenous malformations and assess their relationship to lesion size, location, tissue type involved and vascular architecture.

MATERIALS AND METHODS: Medical records, MRI and histopathology were reviewed in consecutive patients with soft-tissue arteriovenous malformations in a multidisciplinary vascular anomalies clinic. Arteriovenous malformations were divided into those with and without atypical MRI findings (perilesional T2 signal abnormality, enhancement and/or a soft-tissue mass). Lesion location, size, tissue involved and vascular architecture were also compared between groups. Tissue stains were reviewed in available biopsy or resection specimens to assess relationships between MRI findings and histopathology.

RESULTS: Thirty patients with treatment-naïve arteriovenous malformations were included. Fifteen lesions demonstrated atypical MRI. There was no difference in age, gender, lesion size or involved body part between the groups. However, more than half of the atypical lesions demonstrated multicompartmental involvement, and tiny intralesional flow voids were more common in atypical arteriovenous malformations. Histopathology also differed in atypical cases, showing densely packed endothelial cells with connective tissue architectural distortion and edema.

CONCLUSION: Arteriovenous malformations may exhibit features of a vascular tumor on MRI, particularly when multicompartmental and/or containing tiny internal vessels. These features are important to consider in suspected fast-flow vascular malformations and may have implications with respect to their treatment.