Ganglion cysts typically consist of a cyst sac that communicates through a stalk to an underlying joint or tendon sheath (FIG 1).

The cyst sac may have a single cavity or be multilobulated.

Although not a true cyst, lacking an epithelial lining, ganglion cysts are typically filled with a clear, viscous, jelly-like mucinous fluid made up of glucosamine, albumin, globulin, and a high concentration of hyaluronic acid.¹⁷

The tumor is usually a multilobular, well-circumscribed mass, ranging in size from 0.5 to 7 cm.⁶

The color ranges from yellow to deep brown depending on the amount of hemosiderin, histiocytes, and collagen present in the lesion.

These lesions have a thin pseudocapsule. Aggressive lesions may invade adjacent soft tissue, tendon, and capsular structures and can envelop neurovascular bundles. A large study showed joint involvement in one-fifth of all cases.⁷ Long-standing lesions may erode into cortical bone but will not involve cartilage or the medullary canal of bone. Satellite lesions may occur.

Histologically, giant cell tumors contain collagen-producing polyhedral-shaped histiocytes, scattered multinucleated giant cells, and hemosiderin deposits.⁶

Epidermal inclusion cysts are well-circumscribed, firm, and slightly mobile lesions.

They are often superficial and adherent to overlying skin.

They may be flesh-colored, yellow, or white.

They contain a thick, white, keratinous material.

Cysts in the fingertip may erode into the distal phalanx, causing a lytic lesion.

Histologically, they are cysts filled with keratin and lined with epithelial cells.

The true causes of ganglion cysts remain unclear, although multiple theories have been proposed.

Some early investigators theorized that ganglion cysts occurred as the result of synovial herniation and others felt that ganglion cysts resulted from mucoid degeneration.

A more recent theory proposes that ganglion cysts arise from stress at the synovial capsular interface. This stress, such as stretching of the capsular and ligamentous structures, stimulates the production of mucin from modified synovial, mesenchymal, and fibroblast cells, all of which have been shown to produce hyaluronic acid. The mucin then dissects through the capsular and ligamentous tissues, forming the main cyst. The fluid may enter the cyst from the capsular ligamentous interface via a one-way valve type of mechanism and then decrease as the water component is resorbed, accounting for the often-fluctuating cyst size.¹

The cause of giant cell tumors is not known. There is a strong association of giant cell tumors with rheumatoid arthritis. There are no clinical studies associating these tumors with trauma.⁶

Although these tumors are histologically similar to the pigmented villonodular synovitis seen in large joints in the lower extremity, they are thought to be clinically distinct lesions.

Epidermal inclusion cysts occur as a result of trauma when epithelial cells are introduced into the underlying subcutaneous tissues or bone. These cells slowly grow to produce a cyst lined with epithelial cells and filled with keratin.

Ganglion cysts typically arise spontaneously and are most common in the second through the fourth decade but may arise in the pediatric population¹⁹ as well as the aged.

Once present, ganglion cysts tend to fluctuate in size depending on the amount of fluid present in the cyst at any given time. Patients often note that the cyst becomes larger after increased periods of activity and decreases in size with inactivity.

Ganglion cysts tend to be self-limiting and do not typically continue to expand in size.

If left untreated, ganglion cysts can persist for years. They may resolve or rupture spontaneously. One cannot predict how long that they will persist or if and when they will resolve.

Resolution is far more common in the pediatric population.

The lesion begins as a single nodule, becoming multinodular as it enlarges.

Malignant transformation of giant cell tumor of the tendon sheath in the hand has not been reported.⁶

These lesions occur months to years after a traumatic event. They grow slowly to produce a painless mass, most commonly seen in the fingertip.

Malignant transformation of these lesions in the hand has not been reported.¹²

Patients often present with an asymptomatic mass that has been present for weeks to years.

A history of trauma is often absent.

Pain if present is often described as a dull ache. Nocturnal pain is uncommon and pain is more common with active hand use.

Paresthesias are rare but can occur if the ganglion cyst compresses any local nerves.

Patients often report that the mass tends to fluctuate in size, a characteristic typical of ganglion cysts and not typical of other types of soft tissue tumors.

Patients with wrist ganglion cysts—particularly dorsal wrist cysts—will often complain of weakness of grip.

Patients with dorsal wrist ganglion cysts most commonly note a mass over the dorsum of the wrist, typically over the dorsal scapholunate region. In contrast, patients with volar wrist ganglion cysts typically note a mass over the volar aspect of the wrist in the interval between the flexor carpi radialis (FCR) and first extensor compartment tendons.

Volar retinacular cysts or ganglion cysts of tendon sheath usually present as a mass in the palm in the region of the first and second annular pulleys. The cyst is typically fluctuant but may feel like a firm nodule. The cyst is usually slightly mobile but does not often glide with flexor tendon movement.

Degenerative mucous cysts are ganglion cysts that arise from the distal interphalangeal joint, usually in association with underlying osteoarthritis.⁴ Patients often note a painless soft tissue mass that arises from the dorsal surface of the joint, radially or ulnarly (less commonly in the midline), often extending into the eponychial fold region.

Physical examination begins with inspection (FIG 2).

The examiner should palpate the mass for fluctuance and mobility and assess tenderness.

The examiner should assess joint mobility through the range of motion. With the exception of dorsal wrist ganglion cysts, which may cause some loss of wrist dorsiflexion secondary to impingement, loss of joint range of motion suggests the possibility of an underlying joint abnormality.

Giant cell tumors are most common in the fourth to sixth decade, with a slight predominance in women.

Patients typically present with a slow-growing, multilobulated, firm, painless mass present for several months to years.

Lesions usually occur in the radial three digits of the hand on the volar surface. Dorsal involvement, particularly around the distal interphalangeal joint, is not uncommon.⁷

These lesions are typically firmer than ganglion cysts and do not transilluminate.

Large lesions may limit range of motion or result in neuropathic symptoms as a result of compression of digital nerves.

Direct palpation typically reveals a firm, multinodular, nontender lesion.

Loss of range of motion may occur when large lesions occur near the interphalangeal joints.

Patients may have sensory deficits secondary to digital nerve compression. These can be revealed by testing two-point discrimination.

Epidermal inclusion cysts are more common in men than in women and occur in the third to fourth decade.²

Patients commonly present with a painless, slow-growing mass after a laceration, puncture wound, or traumatic amputation of the finger.²

These lesions should be suspected in laborers who have a painless mass in the palm.¹²

Erythematous and painful lesions have been reported. One study reported two cases mimicking a collar-button abscess resulting from rupture of the cyst in the palmar soft tissues.²⁰

These lesions are typically firmer than ganglion cysts and do not transilluminate.

Direct palpation will reveal a lesion that is firm, nontender, superficial, and mobile.

Loss of range of motion may occur when large lesions occur near the interphalangeal joints.

Two-point discrimination testing may reveal sensory deficits secondary to digital nerve compression.

Radiographs are obtained if there is clinical suspicion of an underlying bony abnormality noted on physical examination, such as joint crepitation, swelling, carpal instability, or a history of trauma.

If the clinical findings suggest the possibility of an occult ganglion cyst, or if there is suspicion that the patient may
have a symptomatic intraosseous ganglion cyst, magnetic resonance imaging (MRI) can be a useful tool to confirm the diagnosis (FIG 3B).

Ultrasound can also be used to diagnose ganglion cysts, but this test is examiner dependent and less sensitive and specific than MRI.

Computed tomography (CT) scans are generally obtained only for preoperative planning to better localize and evaluate the bony architecture of intraosseous ganglion cysts.

Plain radiographs show a soft tissue mass. Juxtacortical lesions may show bony erosion.

MRI demonstrates a benign-appearing encapsulated mass, with decreased signal on T1- and T2-weighted images.

Plain radiographs show a soft tissue mass.

A lytic lesion may be seen in the distal phalanx if it erodes into bone.