Presentation
Painless, chronic left knee mass. Physical exam showed a mobile, firm mass localized to the superolateral aspect of the knee. The patient reported no specific trauma, although she is a cheerleader.
Patient Data
MRI without and with IV contrast reveals a 3 cm mass within the lateral aspect of the vastus intermedius muscle with a fluid-fluid level. This demonstrates heterogenous signal intensity, including mild T1 hyperintensity of the posterior dependent component. There is overall minimal enhancement of the mass, with small linear/tubular areas of enhancement seen.
Case Discussion
Considering the history of a chronic palpable mass and MRI findings of a fluid-fluid level with small linear/tubular areas of enhancement, this is likely a venous malformation that bled, resulting in a palpable intramuscular hematoma.
Subsequent ultrasound-guided biopsy and histopathological evaluation revealed fragments of vascular walls and vessels in a background of fragments of skeletal muscle with no signs of malignancy, overall consistent with vascular malformation. Vascular lesions can be divided into vascular tumors and vascular malformations. The former encompasses vasoproliferative lesions such as hemangiomas while the latter includes low and high-flow malformations such as venous and arterial malformations respectively.
MRI is an important modality for imaging vascular malformations as it can clearly show the extent of lesions and can help differentiate between low-flow and high-flow lesions. Venous malformations can appear on MRI as lobulated, multiseptated, enhancing masses exhibiting predominantly isointense T1 signal (relative to skeletal muscle) and high T2 signal. Fluid-fluid levels or high signal on T1 weighted imaging may indicate hemorrhage or stagnant blood within the lesion.
Case courtesy of Dr. Emad Allam - Assistant Professor of Radiology, Loyola University Medical Center.
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