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Original Report |
1 Department of Radiology, University of Michigan Hospitals, 1500 E. Medical
Center Dr., Ann Arbor, MI 48109-0326.
2 Valley Radiology, Ltd., 5322 W. Northern Ave., Glendale, AZ 85301.
3Department of Radiology, Henry Ford Hospital, 2799 W. Grand
Blvd., Detroit, MI 48202.
Received June 26, 2001;
accepted after revision December 12, 2001.
Presented at the annual meeting of the American Roentgen Ray Society,
Washington, DC, May 2000.
Abstract
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CONCLUSION. Foot and ankle ganglia exhibit a spectrum of sonographic appearances from round and completely anechoic masses to hypoechoic, multilobulated, multiseptated masses with dependent debris. All the ganglionic cysts examined in our study showed posterior acoustic enhancement without solid nodules on sonography.
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Sonographic examinations were performed (model HDI 3000 or 5000, Advanced Technology Laboratories, Bothell, WA; or model 5200, Acoustic Imaging, Phoenix, AZ) using linear array transducers ranging from 7.5 to 12 MHz. Sonography was performed by one of seven radiologists experienced in musculoskeletal sonography.
Sonograms from the 10 cases were retrospectively evaluated by consensus of three radiologists for the following sonographic characteristics of the mass: echogenicity; posterior acoustic enhancement; and presence or absence of septations, lobulation, or a solid soft-tissue component. Hypoechoic was defined as less echogenic than surrounding muscle with diffuse low-level echoes within the lesion. Anechoic was defined as sonolucent except for linear septations. From the original sonography reports, the sonographic diagnosis was noted as well as any communication with a specific joint or tendon sheath. The original report was used because more information is available to the sonographer during real-time scanning than is contained in the static images available for retrospective review.
The size of each mass and thickness of any septations were retrospectively measured by one radiologist. Measurements were made using cursor measurements on the film or manual calipers. The use of Doppler evaluation was also noted from the sonograms and sonography reports. Operative reports were available in seven cases (70%), and the origin of any communicating neck found at surgery was noted. Interpretation of the original pathologic specimens was performed by one of nine pathologists. All 10 patients were female; patient age at surgery ranged from 12 to 60 years (mean, 39 years). The time between sonography and surgery ranged from 1 to 377 days (mean, 69 days).
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The preoperative sonography reports provided the diagnosis of a "ganglion cyst" in seven of the 10 cases. In the remaining three cases, the findings were described as "compatible with a ganglion," "ganglion cyst versus synovial cyst," and "synovial cyst." Compared with the surgical findings, the sonography report correctly identified the source of a communicating neck to a joint in two cases and the absence of any neck in one case (Table 1). In two cases, sonography failed to detect a communication that was noted at surgery, and in two additional cases, sonography suggested the communication originated from a different joint or tendon sheath than was noted at surgery. In three cases, no surgical report was available.
Pathology reports were available in all cases. Pathologic findings showed thin-walled cysts containing mucoid material with adjacent mucinous degeneration, which is characteristic of ganglionic cysts. Neither evidence of a synovial lining or solid nodules nor findings of malignancy were noted in the pathology reports.
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Prior reports of sonography of ankle ganglia have included case reports, one of which included pathologic correlation [4]. In contrast, wrist ganglia have been studied extensively with sonography, including several reports with pathologic correlation [5,6,7,8]. Ganglia have been reported to be anechoic or hypoechoic in the wrist [6, 9], which is consistent with our findings for ankle ganglia. Reverberation artifact, which produces linear echoes at the superficial border of a ganglionic cyst (Fig. 1A,1B), should not be mistaken for internal echoes. Reverberation can be eliminated with the use of a standoff pad or copious amounts of coupling gel. Wrist ganglia have been described as typically well-defined, round, or oval cysts with smooth or lobulated borders [5, 7]. Lobulated borders were noted in three cases in our study (30%) and can be prominent (Figs. 3A,3B and 4A,4B). Visualization of a communication with a joint or tendon sheath increases the confidence for the diagnosis of a ganglionic cyst and aids surgical planning [8] (Fig. 4A,4B).
Ganglionic cysts typically show posterior acoustic enhancement, as did all the ganglia in this report. Small ganglionic cysts, however, may show little or no enhanced through-transmission. If a ganglionic cyst is located adjacent to cortical bone, posterior acoustic enhancement may not be visualized in the tissues deep in relation to the mass [6]. However, in such cases increased through-transmission can be noted as increased hyperechogenicity of the underlying cortex (Fig. 4A). Angulation of the transducer can also project the posterior enhancement away from the cortex, which aids visualization.
Septations within ganglionic cysts have not been commonly described in wrist ganglia [5,6,7,8]. However, septations are frequently observed in ankle ganglia, as evidenced by five ganglia (50%) in our study. Septations can be multiple and branching (Fig. 5A,5B). It has been suggested that if septations are noted within soft-tissue masses—especially multiple or thick septations, then suspicion for a malignant process should be increased [10].
In four of our cases, there was a discrepancy between the sonographic and surgical findings regarding the presence of a duct or its origin from a specific joint or tendon sheath (Table 1). These discrepancies were likely caused by one or more of the following factors: incomplete sonographic evaluation that did not detect a neck or duct that could have been visualized with sonography; the presence of an extremely thin or fibrosed duct that was imperceptible with sonography; or the presence of a duct that dissected deep in a region where multiple joints or tendon sheaths are present, thus causing confusion as to the exact source. Complete evaluation of the mass with careful attention to the detection of a joint or tendon communication can aid diagnosis. When a duct dissects deep in a region of multiple joints or tendons, caution in attributing the exact source is warranted. If the duct does not contain fluid, as may be the case with a fibrosed or scarred duct, then the likelihood of visualization with sonography is decreased.
The differential diagnosis of a ganglionic cyst includes anechoic or hypoechoic masses. Common anechoic or hypoechoic masses of the foot and ankle include abscesses, seromas, or hypoechoic lipomas. Clinical history and aspiration can aid in the diagnosis of an abscess. A seroma can be indistinguishable from a ganglionic cyst. A lipoma can be confirmed with MR imaging. A variety of benign and malignant masses can appear hypoechoic. Some solid masses with a homogenous cellular composition, such as neurofibromas and melanomas, can appear hypoechoic with increased through-transmission, simulating a debrisfilled cyst [11, 12].
In cases in which gray-scale imaging does not enable definitive diagnosis of a ganglionic cyst, Doppler assessment can aid evaluation. Doppler evaluation was used in four (40%) of 10 of the patients in this retrospective study and was helpful in detecting internal blood flow and defining adjacent vessels. Internal blood flow on Doppler evaluation or the presence of a nodular component raises suspicion for a malignant neoplasm. In such cases, MR imaging, biopsy, or resection can be used to further evaluate the cyst. A peripheral, dependent, linear, echogenic component was seen in one of the 10 cases and likely was caused by dependent debris. Dependent debris can obscure a nodule. Imaging the patient in a new position can shift the location of dependent debris and exclude this possibility.
There are several limitations to this retrospective report. The study is composed of a relatively small number of cases. The inclusion of only pathologically verified cases is a bias; however, pathologic proof is the strongest gold standard and is needed to establish the sonographic appearance with the highest accuracy. All 10 patients in this study were female. However, the appearance of wrist ganglia has not been shown to significantly differ for female versus male patients; moreover, a sex difference in the appearance of ankle ganglia would not be expected.
The sonographic characteristics of the ankle ganglia were determined by a consensus of three radiologists who were not blinded to the findings from the pathologic specimens, and interobserver variability was not calculated. Surgical reports were available in seven of the 10 cases, which limits the correlation between sonography and surgery for the origin of a communicating neck. Variability in the scanning technique of the sonographers and variability in the interpretation of the surgical specimens by the pathologists are also limitations.
This study does not attempt to determine the accuracy of sonography for the detection of ankle ganglia. It is unknown whether there were sonographic false-positive or false-negative cases during the time period included in this study.
In conclusion, foot and ankle ganglia exhibit a spectrum of sonographic appearances from round and completely anechoic masses to hypoechoic, multilobulated, multiseptated masses with dependent debris. All ganglionic cysts showed posterior acoustic enhancement without solid nodules.
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