The “Little AVM”: A New Entity in High-flow versus Low-flow Vascular Malformations

BACKGROUND Arteriovenous malformations (AVMs) are high-flow lesions with abnormal connections between arteries and veins without an intervening capillary bed. Infrequently, the radiographic diagnosis of a vascular lesion will not support the clinical diagnosis of an AVM. These "discrepant" lesions are not adequately captured within the current classification system and represent a treatment dilemma. The purpose of this study is to review our center's experience with vascular malformations where incongruity in a patient's clinical and radiographic presentation produces a diagnostic and therapeutic challenge. METHODS A retrospective chart review of patients with atypical AVM pre sen ta tions was performed. Parameters reviewed included patient history and demogra phics, clinical presentation, radiological imaging, and treatment modalities. RESULTS Over a 15-year period, we identified 7 cases of vascular malformations with discrepant clinical and radiological findings concerning flow characteristics. All patients were treated based on their radiological diagnosis and most were managed with sclerotherapy. No lesions evolved into a high-flow process, and there was no recurrence at a minimum of 24 months of follow-up. CONCLUSIONS We have identified and described a unique subcategory of vascular malformations that have clinical features of high-flow malformations but radiological features of low-flow malformations. These lesions behave like low-flow malformations and should be treated as such. We propose that complex vascular malformations are best evaluated by both clinical and specialized diagnostic radiological means; the radiologic diagnoses should supplant what is found clinically, and ultimately treatment should be preferentially based on a radiological diagnosis.