Unilateral extremity swelling is a common emergency setting. The most common differential diagnoses include cellulitis, abscess, lymphedema, and venous thrombosis.

Due to an acute onset within hours, an inflammatory process was primarily suspected.

The key findings in the MRI were dilated vessels with extensive flow-voids. The CT shows extensive arteriovenous shunting.

Arteriovenous malformations (AVMs) can occur anywhere in the body but have a predilection towards the head and neck.  

All that is swollen and red is not an infection.