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Original Research |
1 Mallinckrodt Institute of Radiology, Washington University School of Medicine,
510 S Kingshighway Blvd., St. Louis, MO 63110.
2 Department of Orthopedic Surgery, Washington University School of Medicine,
St. Louis, MO.
Received November 18, 2007;
accepted after revision April 4, 2008.
Address correspondence to S. A. Teefey
(teefeys{at}mir.wustl.edu).
Abstract
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MATERIALS AND METHODS. A computer search of sonography and pathology reports for hand and wrist ganglia was performed. All sonography reports and images were reviewed for ganglion size, location, presence of a neck, echogenicity, acoustic enhancement, locules, color Doppler flow, margins, wall thickness, and calcifications and to determine if the ganglion was palpable or collapsed. All pathology reports were reviewed for histologic features that were then correlated with the sonographic images. Ganglia were categorized into three groups: simple, complex cystic, and solid-appearing.
RESULTS. Of 60 ganglia, 34 were complex, 91% of which were located within the dorsal or volar wrist; 97% had well-defined margins; 76%, locules; 68%, acoustic enhancement; 47%, a thick wall; 15%, internal reflectors; and 12%, blood flow. Of the 23 simple ganglia, 11 involved the extensor or flexor tendon sheath, 73% of which were simple. Complex ganglia had a larger mean volume than simple. Three ganglia were solid-appearing. A visible neck was seen in 25% of ganglia.
CONCLUSION. Most ganglia are complex rather than simple on sonography. Complex ganglia are larger than simple ganglia; located within the dorsal or volar wrist; and usually have well-defined margins, thick walls, locules, and acoustic enhancement. A small percentage have blood flow and internal reflectors. Simple ganglia are smaller and can occur within the volar or dorsal wrist, or flexor tendon sheath. Most flexor tendon sheath ganglia are simple rather than complex. Solid-appearing ganglia, although unusual, may mimic a benign neoplasm or synovitis.
Keywords: ganglion • sonography • wrist
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Several studies have shown that sonography is accurate for diagnosing ganglia but few have analyzed the sonographic appearance in a large series [3–6]. Although most have described ganglia as simple or well-defined cystic lesions [4, 7], in our experience, many are complex. In a recent series of 20 patients, Wang et al. [8] also reported that ganglia often do not fulfill the criteria for a simple cyst; sonographic findings included hypoechogenicity, septations, lobulations, and ill-defined walls. The purpose of this study was to analyze the sonographic appearance of a large series of pathologically proven ganglia to alert radiologists to the spectrum of findings, including those that may simulate the appearance of other pathologic processes.
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All sonographic reports were reviewed by one radiologist to determine if a ganglion was reported as palpable and a neck was reported as present (findings that would be difficult or impossible to determine from images alone). All sonographic images were independently reviewed by two radiologists for ganglion size, location, presence of a neck, echogenicity and echotexture (anechoic, hypoechoic, hyperechoic, heterogeneous, homogeneous), posterior acoustic enhancement, internal reflectors (diffuse or tiny discrete reflectors), septations and locules, calcifications, color Doppler flow (peripheral, central, septal), margins (well-defined or ill-defined), and wall thickness (imperceptible or perceptible) and to determine if the ganglion was collapsed. When analyzing cyst echogenicity, low-level echoes in small cysts were discounted as artifact and considered anechoic.
Consensus was reached for any disagreement between the two radiologists. All pathologic reports were reviewed for any further characterization of the ganglion such as the presence of inflammation or hemorrhage; these latter findings were correlated with the sonographic images.
All ganglia were categorized into three groups. A ganglion that was anechoic; unilocular; and had well-defined margins, a thin wall, no color Doppler flow, and variable acoustic enhancement was considered simple (Fig. 1). A ganglion composed entirely of soft tissue with identifiable margins but no identifiable wall and that may or may not have showed color Doppler flow was considered solid-appearing (Fig. 2A, 2B). The rest were categorized as complex cystic and showed two or more of the following findings: septations and locules, internal reflectors, a thick wall, ill-defined margins, color Doppler flow, acoustic enhancement, and a parti ally solid component (Figs. 3 and 4A, 4B).
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All sonograms were obtained in real time with the use of one of several different scanners (ATL HDI 3000 or 5000, Philips Healthcare; Elegra, Acuson Sequoia; or Antares, Siemens Medical Solutions). A variety of variable high-frequency linear-array transducers were used at frequencies ranging from 9 to 13 MHz. Each patient under went sonography of the hand and wrist performed by one of two radiologists who had at least 5 years of experience at the beginning of the study. The sonographic examination was per formed with the patient seated and facing the radiologist. The wrist was placed in a neutral position on an adjustable stand with a small towel placed underneath. Transverse and longitudinal grayscale and color Doppler images of the region of interest were obtained. When indicated, a dynamic examination of the wrist was performed to determine the relationship of the lesion to the underlying structures.
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Of the 23 simple ganglia, 15 (65%) were located within the dorsal or volar wrist and had a mean volume of 144 mm3 (range, 2–1,155 mm3). Eight (35%) involved a flexor tendon sheath or an extensor tendon and had a mean volume of 217 mm3 (range, 48–1,056 mm3). Of the 11 extensor or flexor tendon sheath ganglia, eight (73%) were simple in appearance. Fourteen of 23 (61%) simple ganglia showed posterior acoustic enhancement. The mean volume of a simple ganglion was 170 mm3 (range, 2–1,155 mm3).
Of the 34 complex cystic ganglia, 31 (91%) were located within the dorsal or volar wrist and had a mean volume of 1,094 mm3 (range, 4–7,392 mm3). Three involved a flexor tendon sheath or an extensor tendon. Thirty-three (97%) had well-defined margins, 26 (76%) had septations and locules, 23 (68%) showed posterior acoustic enhancement, 16 (47%) had a thick wall, five (15%) had internal reflectors (diffuse reflectors in three and tiny discrete reflectors in two), and four (12%) showed color Doppler flow (two showed septal, one peripheral, and one peripheral and central flow). Two complex cystic ganglia were partially solid in appearance. The mean volume of a complex cystic ganglion was 1,170 mm3 (range, 4–7,392 mm3).
All three of the solid-appearing ganglia were located within the dorsal wrist, were hypoechoic or heterogeneous, and showed color Doppler flow (two showed central and peripheral flow and one, central flow). Two had ill-defined margins. The mean volume of a solid-appearing ganglion was 105 mm3 (range, 36–144 mm3).
Forty-two of 60 (70%) ganglia were palpable and had a mean volume of 1,015 mm3 (range, 9–7,392 mm3). Twenty-eight of 42 (67%) were complex cystic or solid-appearing and 14 (33%) were simple including all flexor tendon sheath and extensor tendon ganglia. Of the 18 that were not palpable, all were located within the dorsal wrist, with a mean volume of 76 mm3 (range, 2–540 mm3). Nine of 18 (50%) were complex cystic or solid-appearing and nine (50%), simple. A visible neck was present in 15 of 60 (25%) ganglia, 13 (87%) were located within the dorsal or volar wrist, and 11 (73%) were complex cystic. Ten of 60 (17%) ganglia were collapsed; all were complex cystic or solid-appearing and located within the dorsal or volar wrist. Calcification was not present in any ganglion.
Of the 60 pathologically proven ganglia, four had inflammatory changes (chronic in two) and one showed hemorrhage. Three of these ganglia were complex cystic and two, solid-appearing. Three of the four inflamed ganglia (two solid and one predominately solid) also showed color Doppler flow, and the hemorrhagic ganglion showed diffuse reflectors on sonography.
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We also found that complex cystic ganglia are larger than simple ganglia. Nearly all of our complex cystic ganglia were located within the dorsal or volar wrist and had a larger mean volume compared with simple ganglia at that location. In addition, most flexor tendon sheath ganglia were simple and had a smaller mean volume compared with volar and dorsal wrist ganglia. These findings suggest that volar and dorsal wrist ganglia become more complex as they enlarge in the less restrictive wrist soft tissues as opposed to extensor tendon and flexor tendon sheath ganglia that are more constrained by surrounding soft tissues and therefore more likely to remain small and simple.
Nearly all of our complex cystic ganglia had a combination of findings including well-defined margins, thick walls, posterior acoustic enhancement, and septations and locules on sonography. There are several explanations as to why some complex ganglia had a thick wall. It is well known that the wall of a ganglion is composed of compressed collagen fibers [1, 9]. A chronic inflammatory reaction could also cause wall thickening but was described at pathology in only two cases. It is possible that inflammatory changes were not consistently reported. A thick cyst wall would also be expected in a ruptured, collapsed ganglion; of the seven complex cystic ganglia that were collapsed, four had thick walls, suggesting that this was also a cause.
Multiple locules and septations were also frequently seen in complex cystic ganglia. We speculate that changes in ganglion size from repeated cycles of rupture and expansion (due to the formation of new subcysts) may explain this finding. Patients often report such changes in ganglion size over time. It is important to describe the presence of locules in the sonography report because one form of treatment involves aspiration of the cyst contents, which may be unsuccessful in ganglia with multiple locules.
In a minority of the complex cystic ganglia, internal reflectors (diffuse or tiny discrete reflectors) were observed. This may be due to the mucinous, gelatinous contents of ganglion cysts [1]. Mucin has been reported to produce internal reflectors in other cystic lesions, such as mucinous ovarian neoplasms. However, internal reflectors were seen in only five of our ganglia; the rest were anechoic, whether large or small. This may be due to the relative proportion of the constituents of mucin (glucosamine, albumin, globulin, and hyaluronic acid) [9] that may change with the age of the ganglion. Hemorrhage can produce internal reflectors but was reported by pathology in only one of our ganglia.
It is also important to realize that low-level echoes in small cysts may represent artifact. We believe that the low-level echoes in small, but otherwise simple-appearing, ganglia are usually due to beam thickness artifact, near-field reverberations, inherent machine noise, or system gain, all of which are well known to produce such echoes in many different types of cystic structures [10–15]. Thus, in most cases, we considered small ganglia with low-level echoes as simple. In the study by Wang et al. [8], cysts with such echoes were considered hypoechoic and therefore complex rather than simple. However, the cause of the low-level echoes in their small ganglia was not discussed. We believe the internal echoes may have represented artifact and that most small ganglia are simple and not complex.
An atypical appearance that we found that has not been reported previously was the solid-appearing ganglion. All three solid-appearing ganglia were collapsed and showed increased color Doppler flow, both central and peripheral. This sonographic appearance is nonspecific and engendered the differential diagnosis of a benign neoplasm (giant cell tumor of the tendon sheath), synovial proliferation, and a collapsed ganglion in the original sonography report [3]. Only one of these three ganglia was located within the dorsal wrist; in that case, the radiologist diagnosed a collapsed ganglion because of the location, but also included the appropriate differential diagnosis of synovial proliferation. Distinguishing these entities is important because the treatment for a ganglion differs from a benign neoplasm and synovitis; synovitis and ganglia may be treated conservatively with splinting, nonsteroidal anti-inflammatory medications, or aspiration with or without a steroid injection (ganglia) [9], whereas neoplasms are typically excised. Thus, when a solid-appearing lesion with color Doppler flow is identified on sonography, patient history (acute decrease in size) and lesion location (dorsal wrist) may help the radiologist to make the correct diagnosis of a collapsed ganglion. If history and location are not characteristic, the differential diagnosis should include proliferative synovitis, nodular fasciitis, a benign neoplasm such as giant cell tumor of the tendon sheath, or a focal granulomatous process. It is unlikely that MRI would narrow the differential diagnosis; in fact, in one of the above three cases, MRI led to a misdiagnosis of the collapsed ganglion as a giant cell tumor of the tendon sheath.
To our knowledge, the presence of blood flow within ganglia also has not been reported previously. Although we found that the majority of ganglia were completely avascular on color Doppler sonography, a small number of complex cystic ganglia did have demonstrable color Doppler flow, likely due to superimposed inflammation, as was reported in one case at pathology. Although unusual, its presence should not dissuade the radiologist from diagnosing a ganglion when a multiloculated cystic lesion of the hand or wrist with color Doppler flow is identified. It is important to use a copious amount of gel with minimal transducer pressure when scanning a superficial structure such as a ganglion so as not to compress tiny vessels and reduce blood flow. Optimization of Doppler technical parameters, in particular, using the highest possible Doppler transmit frequency, is also critical in detecting low volume and low velocity flow.
In our series, nonpalpable ganglia had a much smaller mean volume than palpable ganglia but were not always simple in appearance. Despite their small size, 50% were complex. All were located deep within the dorsal wrist; none was located within the flexor tendon sheath or extensor tendon, as would be expected given the more superficial location of these latter ganglia. Nonpalpable dorsal ganglia are referred to as occult dorsal ganglia and can be a source of unexplained wrist pain and tenderness, likely due to predynamic scapholunate instability. Although we did not analyze the accuracy of sonography for diagnosing occult dorsal ganglia in this study, previous reports have shown that it is accurate for detecting such cysts [5, 6, 16].
Equally important as diagnosing a ganglion is identifying the neck, which must then be traced to its origin at the time of surgery to avoid recurrence [9]. Nearly all our ganglia that had visible necks were located within the dorsal or volar wrist, likely because of the less restrictive wrist soft tissues that allow dissection, and were complex cystic. It is well known that dorsal wrist ganglia are attached by a pedicle of variable length to the scapholunate ligament. If the pedicle is long, the main cyst may be found at a location remote from the ligament. In a recent case at our institution, an apparent volar wrist ganglion had a very long neck, the origin of which was traced to the dorsal scapho lunate ligament on sonography. According to the hand surgeon, if we had not identified the origin, the ganglion may not have been completely excised, increasing the risk for recurrence.
Volar wrist ganglia, which can originate from the capsule of either the scaphoradial or scaphotrapezial joint [1], can also dissect extensively into the surrounding soft tissues, making identification of their origin difficult. Our study did not evaluate the accuracy of sonography for identifying the origins of ganglia because this information was not stated in most operative reports; however, we identified a neck in only 25% of cases. This was in part because of the retrospective nature of the study and the use of lower frequency transducers in the early phase, but also because 13% of our ganglia were of flexor tendon sheath origin; these cysts are tethered by the pulley system and thus would not have a visible neck.
This study has several limitations. Because of its retrospective nature, we found it difficult to characterize the sonographic features of tiny ganglia on hard-copy images. This was also likely caused by the use of older equipment and lower-frequency transducers during the early phase of the study. The absence or presence of a neck and collapse could not be confirmed at surgery because these findings were not reported in most cases. It is also likely that more ganglia were inflammatory or hemorrhagic than was described in the pathology reports. Finally, only a small number of ganglia were solid-appearing, but given the large number of ganglia in the study, this small number is likely in keeping with what would be expected.
In summary, our study showed that most ganglia are complex rather than simple on sonography. We found that complex ganglia are larger than simple ganglia; occur within the dorsal or volar wrist; and typically have well-defined margins, thick walls, locules, and posterior acoustic enhancement. A small percent have color Doppler flow and internal reflectors. Simple ganglia most commonly occur within the dorsal or volar wrist but may occur in the flexor tendon sheath. In fact, most flexor tendon sheath ganglia are simple rather than complex. Solid-appearing ganglia, though uncommon, can mimic the appearance of a benign neoplasm or proliferative synovitis; it is important to recognize this so as to generate the appropriate differential diagnosis.
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