MuscSktf13-Ganglion

Findings:

Patient presented with a swelling over the right finger. On the MRI there is a hypointense lesion on the T1W images along the dorsum of the right ring finger, at the level of the distal interphalangeal joint. It is hyperintense on the T2W and GRASS images.

Discussion: 

A ganglion is a tumor like lesion of unknown origin that arises in the juxtaarticular soft tissues. They are usually seen in young adults and are more common in females. Patients usually present with a palpable mass. Tenderness, mild pain, or functional impairment may be present. The lesions may enlarge or decrease in size, or resolve spontaneously. Rarely, they may compress adjacent structures and be the cause of nerve palsy. Ganglions may also extend from the joint into the adjacent muscle.

Etiology:

Uncertainty exists regarding the origin of ganglion cysts. It is widely believed that cyst formation occurs due to mucoid degeneration of collagen and connective tissues. This implies that a ganglion represents a degenerative structure that houses the myxoid changes of connective tissue. Another theory attributes cyst formation to trauma or tissue irritation. Modified synovial cells lining the synovial-capsular interface are stimulated to produce mucin. Mucin dissects along the attached joint ligament and capsule to form capsular ducts, which function as valve-like structures producing lakes. The ducts and lakes of mucin eventually coalesce to form a solitary ganglion cyst.

Common sites for ganglions are:
The wrist - on the back ("dorsal wrist ganglion"), on the front ("volar wrist ganglion"), or sometimes on the thumb side. These come from one of the wrist joints, sometimes aggravated by a wrist sprain.
The palm at the base of the finger ("flexor tendon sheath cyst"). These come from the tube which holds the finger tendons in place, and are often due to tendon irritation - tendinitis.
The back of the end joint of the finger ("mucous cyst"), next to the base of the fingernail. These can cause a groove in the fingernail, or rarely can become infected and lead to a joint infection. These are usually due to some arthritis or bone spurs in the joint.
70% of ganglions are located around the wrist and account for 50% to 70% of all soft tissue masses of the wrist. Less commonly, ganglions arise in the foot, although they may develop adjacent to any joint or tendon sheath.

Pathology:

Most ganglions are small, measuring 1.5 to 2.5 cm, without communication to the joint space, although occasionally a communication to the joint may be demonstrated. Lesions may be unilocular or multilocular, are typically rounded to lobular, and are adjacent to joint capsules or tendon sheaths. Microscopically, thick-walled cystic spaces are characteristic and are associated with myxoid areas, which may be outside the cystic spaces. The lesion is surrounded by dense connective tissue and is filled with viscous, gelatinous fluid rich in hyaluronic acid and other mucopolysaccharides. There is no discernible internal lining cell.

Imaging:

Radiographs may be normal or may reveal a soft tissue mass. The adjacent bone occasionally demonstrates evidence of bone resorption or periosteal new bone. Ultrasound and MRI are both effective in detecting ganglions. Ultrasound readily detects even small ganglion cysts, which may be identified as small fluid collections, appearing as well-defined homogeneously anechoic masses. Occasionally, septations may be present. Long-standing cysts, cysts with complex contents, or cysts after aspiration may demonstrate internal echoes mimicking a solid tumor. Occasionally, a communication to the joint or “pseudopodia” extending toward the joint may be seen.
Ganglions typically look like cysts on MRI and are hypointense on T1W images and hyperintense on T2W images, or they may be isointense or slightly hyperintense to muscle on T1W images. They may demonstrate considerable heterogeneity on T2W images. Rim and septal enhancement may be seen after gadolinium administration, although small lesions may show more extensive and diffuse immediate enhancement. MRI clearly localizes the lesion and identifies its relationship to adjacent structures, including vessels, tendons, and nerves. Ganglions may be associated with major vessels in 10% to 20% of cases, making aspiration difficult. When adjacent nerves are compressed, MRI may reveal abnormalities in the corresponding muscle groups.

Treatment:

Aspiration: It involves aspiration alone or followed by steroid injection. This is usually successful for tendon sheath ganglions in the hand and digits. Caution should be exercised when performing multiple steroid injections to avoid the complications of skin and fat atrophy and thinning, as well as hypopigmentation.

Excision: Surgical treatment involves total ganglionectomy with removal of a modest portion of the attached capsule. Surgical treatment of dorsal carpal ganglion cysts should be directed toward removal of the cyst and attachments to the scapholunate ligament. Excision of a volar carpal ganglion involves cyst removal along with removal of attachments to the radiocarpal capsule of the scaphotrapezial joint. A mucous cyst can be approached through a curved oblique incision, or an H-shaped incision, over the dorsal distal interphalangeal joint. If the overlying skin cannot be separated from the cyst, it is excised in an elliptical fashion. The cyst is dissected proximally to the joint capsule of the distal interphalangeal joint and then excised along with the joint capsule. If an osteophyte is present, it is usually removed at the time of mucous cyst excision. If skin coverage is insufficient, a local flap, skin graft, or both may be required for subsequent closure.