This 11-year-old female presents with a lump on the third digit of her foot that has been present for more than a year. The lump is mobile on exam, and is not growing or causing pain. She has no history of surgery or trauma.
Evaluation of masses of the extremity usually begins with plain radiographs (not available in this case). What is the diagnosis? What are some of the advantages of MRI vs. plain films in cases of extremity masses?
The cause of this patient’s lump is a ganglion cyst (pseudocyst). A ganglion is really a pseudocyst that occurs because a capsule or tendon sheath is deficient or has a “microtear.” Fluid diffuses into the surrounding soft tissues where it is walled off by fibrous tissue. Ganglia exhibit NO epithelial lining like a true cyst. The origin of the ganglion might be seen as a small “tail” or “nubbin” from whence it came.
A rarer diagnosis would be epidermoid or cystic schwannoma. The green arrows demonstrate small intertarsal bursal cysts (image 3). Otherwise, her foot is normal. The advantage of MRI vs. plain radiography is that MRI provides for soft tissue resolution and is helpful in discriminating among cartilaginous lesions, osseous lesions, muscular or tendon-slip lesions, and other connective tissue lesions. Plain films have a cost advantage and can exclude bone lesions such as fracture or osteochondroma. But, near to the trunk of the body, avoid any x-ray or radiograph in persons of childbearing age when you can. Substitute ultrasound or MRI. For more case review, check out MRI Online.