Clinical History: A 41 year-old male presents with a history of lateral knee pain for 6 months. (1a) Axial proton density-weighted with fat saturation and (1b) Sagittal T1-weighted images of the left knee are provided. What are the findings? What is your diagnosis?
1a
1b
Figure 1:
(1a) Axial proton density-weighted with fat saturation and (1b) Sagittal T1-weighted images of the left knee.
Findings
2a
2b
Figure 2:
The (2a) axial proton density-weighted image with fat saturation demonstrates a large, lobulated fluid signal focus (arrows) within Hoffa's fat pad centrally and extending laterally. This arises from the distal anterior cruciate ligament fibers. Thin internal septa are also present. The (2b) sagittal T1-weighted view demonstrates the well demarcated intermediate signal intensity lesion (arrow) relative to the surrounding high signal intensity fat.
Diagnosis
Infrapatellar (Hoffa’s fat pad) ganglion cyst arising from the anterior cruciate ligament.
Introduction
Soft tissue ganglia are a very common finding with MR Imaging, particularly about the wrist, often presenting due to mass-like symptoms. However, they are also commonly found in other parts of the body and can be sometimes confused with other benign and malignant processes. Intraosseous ganglia are also very often identified on MR scans.
Histology
Soft tissue ganglia are fluid-filled sacs containing mucinous material which have a thin connective tissue capsule but no synovial lining. Though the etiology is not clear, they may represent a synovial herniation or coalescence of small degenerative cysts arising from the tendon sheath, joint capsule, or bursae.1 Although they are histologically distinct from synovial cysts, which have a true synovial lining, these entities are typically indistinguishable on imaging.2 Histologically, there are no major differences between intraosseous ganglia and extraosseous ganglia. They can be of primary etiology or secondary due to an inflammatory process in the joint.3 Intrasubstance anterior cruciate ligament ganglia are due to mucinous degeneration of connective tissue.4
Clinical Presentation
Often both soft tissue and intraosseous ganglia are incidental findings with no clinical symptoms. However, when large or adjacent to neurovascular structures, symptoms due to mass effect may be present. Soft tissue ganglia often present as non-painful, round, firm, smooth “masses” about the joints (3a). They are variable in size at presentation, often changing depending on the level of activity. Ganglia are the most common soft-tissue mass in the foot and ankle.5 Though usually asymptomatic, ankle ganglia can present with pain, weakness, swelling, osseous erosion, and tarsal tunnel syndrome.2 When found in the knee, pain, clicking, stiffness, incomplete extension of the knee and pain at the extremes of motion are commonly encountered symptoms. Occasional findings include a palpable mass and bone erosion (4a). Cysts anterior to the ACL tend to limit extension and those posterior to the PCL to limit flexion.6
3a
Figure 3:
A patient presents with a dorsal wrist "mass" which developed one month after injury. An axial proton density-weighted sequence is provided. A ganglion (arrow) is demonstrated to arise from the lunate-capitate articulation with its epicenter dorsal to the extensor carpi radialis tendon (arrowhead).
4a
Figure 4:
A fat-suppressed proton density-weighted coronal image in another patient with chronic pain demonstrates an anterior cruciate ligament ganglion eroding into the lateral femoral condyle (arrow). Note the surrounding marrow edema (arrowheads).
MR Evaluation
Soft tissue ganglia appear as simple, single lobule to multi-septated and/or multi-lobulated fluid signal foci, usually contiguous with a joint capsule or tendon sheath (5a-7a). Intraosseous ganglia present as fluid signal foci, with or without surrounding marrow edema, usually in close proximity to an articular surface. Ganglia are usually of low to intermediate signal on T1-weighted and of increased signal on T2-weighted sequences, similar to pure fluid. However, due to hemorrhage or high proteinaceous content, they can be of increased signal on T1-weighted sequences. Mild peripheral or septal enhancement may be seen on contrast enhanced imaging.
5a
Figure 5:
A sagittal T2 image of the proximal calf demonstrating a large, lobulated ganglion (arrows) arising from the proximal tibiofibular joint extending intramuscular into the peroneus longus muscle, presenting as a palpable mass.
6a
Figure 6:
A coronal STIR sequence of the left hand demonstrating an unusually large, lobulated ganglion (arrows) of the volar aspect of the small finger, superficial to the flexor tendons.
7a
Figure 7:
An axial T2-weighted image in a patient with a palpable abnormality reveals a lobulated, septated, multifocal ganglion (arrows) with components superficial to the peroneal tendons (arrowheads) at the tip of the fibula. The lesion lies lateral to the sinus tarsi (asterisk), likely arising from the cervical ligament.
Especially when large, soft tissue ganglia may present with osseous erosion (8a,9a). Intraosseous ganglia may also extend outward through cortex and communicate with an extra-osseous component. Ganglia may also present with neurological findings due to mass effect upon nerves. (10a-14a) In a study on knee ganglia, discrete intraosseous ganglia were observed in 66% of studies with intrasubstance anterior cruciate ligament ganglia and 77% of patients with mucoid degeneration.7
8a
Figure 8:
A sagittal T1 sequence with anterior cruciate ligament graft ganglion (arrow) expanding the tibial tunnel. The interference screw (arrowhead) is also migrated distally.
9a
Figure 9:
Mucinous degeneration of the proximal medial collateral ligament with associated intraosseous ganglion (arrow) and moderate surrounding reactive marrow edema on this fat-suppressed proton density-weighted coronal image.
10a
Figure 10:
This patient presents with pain and inability to extend the ring and small fingers. A ganglion (arrow) arising from the fifth carpometacarpal articulation is present, displacing a branch of the ulnar nerve.
11a
Figure 11:
The corresponding STIR image on the same patient as in J reveals edema and mild atrophy of the intrinsic musculature medial and lateral to the ring metacarpal (arrowheads), consistent with denervation change.
12a
Figure 12:
This patient presented three months following injury with pain and limited range of motion at the shoulder. The sagittal T2 image of the left shoulder demonstrates a large ganglion within the spinoglenoid notch and suprascapular notch (arrows) with resulting denervation injury of the infraspinatus muscle evidenced by mild muscle atrophy and subtle intramuscular edema (arrowheads).
13a
Figure 13:
Two months of pain, swelling, and medial foot tingling. An axial T1-weighted image in a patient with a two month history of pain, swelling, and medial foot tingling reveals a ganglion within the tarsal tunnel (arrow) contiguous with the flexor hallucis longus and flexor digitorum longus tendons.
14a
Figure 14:
A Sagittal T2-weighted image with fat saturation from the same patient as 13a demonstrates abductor hallucis and flexor digitorum brevis muscle edema (arrowheads) consistent with early denervation change.
Discussion
The pathogenesis of ganglia is uncertain with theories being that they develop from an outpouching of a joint capsule or as the result of soft tissue irritation or chronic damage leading to connective tissue degeneration and subsequent mucinous fluid production rich in hyaluronic acid from lining cells.8
The term “complex ganglion” is one not often found in the literature. The author and colleagues have used this term in the setting of a ganglion that is not of simple fluid signal, with this often due to hemorrhage. However, by ultrasound, the term complex ganglion has been used to describe ganglia that are larger, likely due to less constraint of surrounding soft tissues, containing septations, thick walls, and locules.9 The loculations and septa may be due to episodes of rupture and subsequent recurrence.9 Since ganglia can also collapse following rupture, they may have the appearance of a solid mass, similar to a giant cell tumor of tendon sheath.
Treatment
Usually ganglia do not require treatment. However, when necessary, due to pain, mass effect on surrounding structures, limitation of range of motion or for cosmetic reasons, they can be drained or surgically removed. The surgical recurrence rate has been found to be as low as 4% in one study10 and up to 40% in another study.11
Differential Diagnosis
The differential diagnosis of these cystic lesions includes synovial myxoma12, meniscal or parameniscal cyst, synovial cysts, pigmented villonodular synovitis, synovial hemangioma, aneurysm (15a,16a), and synovial or other sarcoma (17a-19a). In general, ganglion cysts are more well defined and in particular more homogeneous than the other diagnostic considerations. It is important to recognize that lesions that are not of typical fluid signal intensity on T1 or T2-weighted images often do not represent a ganglion.
15a
Figure 15:
A T1-weighted axial image in a patient with a palpable hand mass. The "mass" (arrow) has central increased T1 signal suggesting blood products.
16a
Figure 16:
Same patient as 15a. A STIR coronal image reveals central, "swirling" increased T2 signal (arrow). A low signal intensity rim is seen on both the T1 and STIR images. Pulsation artifact in the phase encoding direction (arrowheads) is also present. The diagnosis in this case is a pseudoaneurysm arising from a branch of the radial artery.
17a
Figure 17:
This patient presented with a palpable abnormality suspected to be a ganglion. Though this is of fluid signal on the T2 weighted image provided (arrow), it was of muscle signal intensity on the T1 views, and the margins are not as well-defined as is typical for a ganglion. At surgery, the mass was found to be a clear cell sarcoma.
18a
Figure 18:
Another patient similar to 17a presenting with a palpable abnormality reportedly present for 2-3 years. The fat-suppressed proton density axial image reveals a heterogeneous increased signal intensity lesion (arrow) encasing the abductor pollicis longus tendon (arrowhead).
19a
Figure 19:
Same patient as 18a. On the T1-weighted coronal image, the margins are sharp (arrowheads). However, note the internal areas of decreased signal intensity and signal characteristics similar to muscle. The patient was found to have a synovial sarcoma at surgery.
Conclusion
MR is considered to be the gold-standard for ganglion imaging. The full extent of the lesion as well as its effect on surrounding soft tissues and osseous structures can be evaluated. Though ganglia are usually characteristic lesions on MR, other etiologies, including malignancies, can appear similar, and thus careful consideration of the morphology and signal characteristics of the mass is required in order to avoid a misdiagnosis.
References
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3 Schajowicz F, Sainz MC, Slullitel JA: Juxta-articular bone cysts (intraosseous ganglia). J Bone Joint Surg Br 1979; 61:107-116
4 Fealy S, Kenter K, Dines JS, Warren RF. Mucoid degeneration of the anterior cruciate ligament. Arthroscopy 2001; 17:37-39
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8 Ghazal L, Chandrashekar S, Fersia O, Hirst P. MRI misinterpretation of a large infrapatellar fat pad ganglion of the knee: a case report and literature review. The Internet Journal of Radiology 2010; 13 (1)
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10 Thornburg LE. Ganglions of the hand and wrist. J Am Acad Orthop Surg. Jul-Aug 1999; 7(4):231-8
11 Chloros GD, Wiesler ER, Poehling GG. Current concepts in wrist arthroscopy. Arthroscopy. Mar 2008; 24(3):343-54
12 Lee KR, Cox GG, Neff JR, Arnett GR, Murphey MD. Cystic masses of the knee: arthrographic and CT evaluation. AJR Am J Roentgenol 1987; 148:329-334