Bump on Knee


  • Slide

A 61-year-old woman presents with a 7-month history of a bump on the front of her left knee. The lesion is slightly tender but otherwise is asymptomatic. She is concerned that the lesion may be cancerous. She has no other medical problems and takes vitamin D daily. On physical examination, a firm subcutaneous tumor is noted on the left knee measuring 8 cm without overlying skin changes. She has no other similar lesions elsewhere on her body.

Ganglion cysts are common, benign soft tissue tumors with mucin-filled collections and a stalk typically attaching to the underlying space.1 Ganglion cysts were first described by Hippocrates as flabby ganglionic (translates to a knot or swelling under the skin in...

Submit your diagnosis to see full explanation.

Ganglion cysts are common, benign soft tissue tumors with mucin-filled collections and a stalk typically attaching to the underlying space.1 Ganglion cysts were first described by Hippocrates as flabby ganglionic (translates to a knot or swelling under the skin in ancient Greek) tumors, containing only mucoid flesh.2

Women are reported to be affected at a 3-fold higher rate than men, and ganglion cysts are most common in young adults.3 The most common location of ganglion cysts is the dorsal wrist, with 70% of soft tissue ganglia arising in this location from the dorsal aspect of the scapholunate ligament. The second most common location is the volar wrist.1,4,5 Degenerative joint disease is the main predisposing factor but ganglion cysts may also be related to trauma or stress of the joints, rheumatoid arthritis, gout, and systemic lupus erythematosus.6

The exact etiology of ganglion cysts is not completely known. The fluid may arise from within the joint, pumped into the cyst by the motion of the joint. Alternatively, fluid may also arise from an extra-articular degenerative process or from the mesenchymal cells within the cell wall. It is possible that a combination of these mechanisms can contribute to development of ganglion cysts.5 Joint stress is believed to play a role as well, leading to an opening in the joint capsule and allowing leakage of synovial fluid.5 However, the current consensus is that the origin of ganglion cysts is noninflammatory in nature as demonstrated by pathologic studies showing no pericystic inflammatory changes.5

On physical examination, ganglion cysts are usually 1- to 2-cm cystic structures that feel like a firm rubber ball that is tethered in place by an attachment to the underlying space.5 They most commonly occur on the hand and wrist, followed by the foot and ankle, though they can occur in any joint.2,5 Typically no overlying warmth or erythema is found and the cyst will readily transilluminate.5 The cysts may arise from the joint capsule, ligaments, tendon sheaths, bursae, or subchondral bone.6 While pain, radiating aches, and paresthesia are possible, the majority of patients are asymptomatic except for swelling.4 In patients who present with pain, the pain is more likely to be annoying than debilitating.4

Analysis of the cystic fluid shows a gelatinous material containing mainly hyaluronic acid and lesser amounts of glucosamine, globulins, and albumin. The fluid is also much thicker than intra-articular synovial fluid.5 Evaluation via electron microscopy demonstrates that the wall of the ganglion is composed of randomly oriented sheets of collagen arranged in loose layers, one on top of another.5

Despite being similar in appearance, ganglion cysts should be histologically differentiated from synovial cysts as synovial cyst treatment involves treating an underlying cause.7 Ganglion cysts will not have a synovial cell lining.6,7 Rather, ganglion cysts are delineated by dense fibrous connective tissue. On ultrasonography, ganglion cysts are also much harder to compress because of their dense fibrous connective tissue and thick viscosity.7

Clinical presentation is usually adequate for diagnosis.5 However, in cases where visualization is warranted, imaging may be employed. Ultrasonography should be the initial imaging choice as this is a low-cost and widely available modality. Small ganglion cysts (<10 mm) often appear hypoechoic without posterior acoustic enhancement and larger ganglion cysts will more likely appear anechoic with posterior acoustic enhancement.8 Plain radiography is generally not recommended from a cost-benefit perspective unless the patient presents with trauma or other concern for bone involvement.9,10 Magnetic resonance imaging (MRI) has a 94.7% sensitivity for the evaluation of ganglion cysts, with the typical appearance of smooth, well-defined, thin-walled, unilocular, and homogeneously T2-hyperintense lesions. A more complex, but equally benign appearance with several septa, internal T2-hypointense debris, and even osseous loose bodies may occur. Stalk attachment is common as well.6

Other soft-tissue tumors and tumor-like lesions should also be considered in the differential diagnosis and can be distinguished via the high soft-tissue resolution of MRI. For example, in pigmented villonodular synovitis, a benign proliferative disorder of the synovium, MRI reveals a heterogeneous signal intensity because of the fat, collagen, and hemosiderin it contains in T2W signals.10 Magnetic resonance imaging provides the greatest sensitivity for identifying the unique soft tissue profile of the ganglion cyst and should be considered the gold standard in characterizing any periarticular cystic lesion.6

Most patients seek evaluation and treatment for ganglion cysts because of cosmetic concerns or to rule out malignancy.4 For asymptomatic patients, reassurance, and observation are appropriate.4 The spontaneous resolution rate ranges from 40% to 58%.4 Otherwise, aspiration remains the simplest way to treat ganglion cysts with the drawback of having high recurrence rates ranging from 15% to 69%.4 The more invasive, yet most effective way to treat ganglion cysts is surgical excision of the whole ganglion including the cyst and its attachments, originally introduced by Angelides and Wallace.11 Recurrence after surgical treatment ranges from 0 to 31.2%.4

Other nonsurgical techniques include steroid injections, sclerotherapy, hyaluronidase, immobilization, and the thread technique which may be combined with aspiration. The evidence for the efficacy of these nonsurgical treatments is mixed and they generally are considered to be ineffective.4 However, these nonsurgical options can be explored if the patient is resistant to operative procedures. Though surgical treatment is most effective, several complications may occur including wound infection, neuroma formation, hypertrophic scar, and damage to nearby nerves and arteries.4 Thus, conservative treatments may be considered prior to more invasive options.1

In our case, ultrasonography of the patient’s knee showed a hypoechoic superficial cystic area measuring up to 8.6 cm with an apparent tract to the anteromedial joint space. Further evaluation of the knee via MRI showed a ganglion cyst arising from the anterior horn of the lateral meniscus. The patient met with orthopedic surgery to discuss surgical management and, after discussing the risks and benefits of surgery, the patient decided to observe the lesion at this time.  

Harrison Zhu, BSA, is a medical student at Baylor College of Medicine in Houston, Texas. Tara L. Braun, MD, is a dermatologist at Elite Dermatology in Houston, Texas.


1. Meyerson J, Pan YL, Spaeth M, Pearson G. Pediatric Ganglion cysts: a retrospective review. Hand (N Y). 2019;14(4):445-448. doi:10.1177/1558944717751195.

2. Camasta CA. Excision of the ganglion cyst. The Podiatry Institute. 1993. http://www.podiatryinstitute.com/pdfs/Update_1993/1993_33.pdf

3. Thornburg LE. Ganglions of the hand and wrist. J Am Acad Orthop Surg. 1999;7(4):231-238. doi:10.5435/00124635-199907000-00003

4. Suen M, Fung B, Lung CP. Treatment of ganglion cysts. ISRN Orthop. 2013;2013:940615. doi:10.1155/2013/940615

5. Gude W, Morelli V. Ganglion cysts of the wrist: pathophysiology, clinical picture, and management. Curr Rev Musculoskelet Med. 2008;1(3-4):205-211. doi:10.1007/s12178-008-9033-4

6. Neto N, Nunnes P. Spectrum of MRI features of ganglion and synovial cysts. Insights Imaging. 2016;7(2):179-186. doi:10.1007/s13244-016-0463-z.

7. Giard MC, Pineda C. Ganglion cyst versus synovial cyst? Ultrasound characteristics through a review of the literature. Rheumatol Int. 2015;35(4):597-605. doi:10.1007/s00296-014-3120-1

8. Wang G, Jacobson JA, Feng FY, Girish G, Caoili EM, Brandon C. Sonography of wrist ganglion cysts: variable and noncystic appearances. J Ultrasound Med. 2007;26(10):1323-1328. doi:10.7863/jum.2007.26.10.1323

9. Wong AS, Jebson PJ, Murray PM, Trigg SD. The use of routine wrist radiography is not useful in the evaluation of patients with a ganglion cyst of the wrist. Hand (N Y). 2007;2(3):117-119. doi:10.1007/s11552-007-9032-8

10. Sayit E, Sayit AT, Bakirtas M. Ganglion of the foot and ankle: imaging and pathological findings, differential diagnosis, and operative management. J Orthop Res Physiother. 2015;1;005.

11. Angelides AC, Wallace PF. The dorsal ganglion of the wrist: its pathogenesis, gross and microscopic anatomy, and surgical treatment. J Hand Surg Am. 1976;1(3):228-235. doi:10.1016/s0363-5023(76)80042-1

Next hm-slideshow in Dermatology Clinics