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Original Report |
1 Department of Radiology, Mayo Clinic, 4500 San Pablo Rd., Jacksonville, FL
32224-3899.
2 Department of Radiology, Advanced Diagnostics, 8307 Knight Rd., Houston, TX
77054-3905.
3 Department of Radiologic Pathology, Armed Forces Institute of Pathology,
Walter Reed Army Medical Center, Bldg. 54, Alaska and Georgia Aves.,
Washington, DC 20306-6000.
4 Department of Radiology, National Naval Medical Center, 8901 Wisconsin Ave.,
Bethesda, MD 20889.
5 Department of Radiology and Nuclear Medicine, Uniformed Services University,
4301 Jones Bridge Rd., Bethesda, MD 20814.
Received August 9, 2002;
accepted after revision October 24, 2002.
The opinions and assertions contained herein are the private views of the
authors and are not to be construed as official or as reflecting the views of
the Department of the Army, Department of the Navy, or the Department of
Defense.
Abstract
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CONCLUSION. The diagnosis of fibroma of the tendon sheath can be suggested when MR imaging reveals a focal nodular mass adjacent to a tendon sheath with decreased signal on all pulse sequences and little or no enhancement.
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Scant documentation of the radiologic appearance of fibroma of the tendon sheath is found in the literature. We retrospectively reviewed our experience with fibroma of the tendon sheath to identify the MR imaging characteristics of this lesion.
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MR imaging was performed in all patients on high-field-strength (1.0-T or 1.5-T) magnets. The MR imaging sequences performed included spin-echo T1-weighted (TR range/TE range, 450-800/10-22) in all patients, conventional spin-echo T2-weighted (2000-2500/80-90) (n = 3), fast spin-echo T2-weighted (3000-6000/68-101) (n = 3), and short tau inversion recovery (1700-5500/30-60; inversion time, 130-150 msec) (n = 4). Gadolinium-enhanced T1-weighted imaging (450-763/15-23) was performed in all patients, with fat suppression performed in five patients. We analyzed the MR images for signal intensity, signal homogeneity, enhancement pattern, lesion size and location, and proximity of the lesion to a tendon. Enhancement was graded as absent or present. If present, the pattern of enhancement was characterized as homogeneous, heterogeneous, peripheral, or central. Skeletal muscle and fat were used as the reference tissue for all MR imaging sequences. All images were analyzed by four radiologists working in consensus.
This study was conducted with the approval of the institutional review board of the Mayo Clinic in accordance with the requirements for a retrospective review.
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Radiographs in one patient had a normal appearance, and in the other, showed a soft-tissue mass with mild scalloping of the adjacent bone. No erosion, periosteal reaction, cortical disruption, or soft-tissue calcification was evident.
MR imaging showed five (83%) of the six lesions to be mildly to moderately heterogeneous, with heterogeneity more pronounced on T2-weighted images. One of these heterogeneous lesions was homogeneous on T1-weighted images. The remaining lesion was homogeneous on both T1- and T2-weighted images. On T1-weighted images, five lesions (83%) showed a signal intensity equal to or less than that of skeletal muscle (Figs. 1A, 1B, 1C and 2A, 2B, 2C, 2D), with the remaining lesion showing a signal intensity slightly greater than that of skeletal muscle. On T2-weighted images, three lesions (50%) showed decreased signal intensity equal to or less than that of skeletal muscle (Figs. 1A, 1B, 1C and 2A, 2B, 2C, 2D). Two of these lesions showed intermediate signal intensity greater than that of muscle and similar to that of fat (Figs. 3A, 3B and 3C), whereas the remaining lesion showed an intermediate signal centrally with decreased signal peripherally. Enhancement patterns varied: two lesions (33%) showed no enhancement, one lesion (17%) had mild peripheral enhancement, and three lesions (50%) showed moderate to marked diffuse enhancement. In two patients, short tau inversion recovery sequences showed decreased signal intensity similar to that of T2-weighted images; in the other two patients imaged with this sequence, lesions showed nonspecific increased signal intensity.
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Five of the patients in our study had tumors that showed a signal intensity similar to or less than that of skeletal muscle on T1- weighted spin-echo MR images (Figs. 1A, 1B and 1C), as would be expected in a predominantly fibrous lesion. Two of these patients also showed a signal intensity similar to that of skeletal muscle on both T2-weighted spin-echo and fast spin-echo MR images (Figs. 1A, 1B, 1C and 2A, 2B, 2C, 2D), with no enhancement after administration of contrast material (Figs. 1A, 1B, 1C and 2A, 2B, 2C, 2D). Microscopic examination in one of these patients showed predominantly acellular fibrous tissue with areas of hyalinization (Figs. 2A, 2B, 2C and 2D). These imaging and microscopic features are similar to the case reported by Misawa et al. [4].
Fibroma of the tendon sheath can have different imaging features if areas of increased cellularity or myxoid change are present. In our study, a lesion adjacent to the flexor carpi ulnaris showed a T1-weighted signal intensity equal to that of muscle; with T2-weighted imaging, it showed signal intensity approximately equal to that of fat centrally and somewhat less than that of fat peripherally (Figs. 3A, 3B and 3C). The tumor also showed enhancement that was most marked centrally, and it contained central areas of increased cellularity and myxoid change on a background of vascular slit-like channels within hyalinized stroma. This microscopic appearance reflects the MR imaging findings and accounts for the enhancement pattern, as previously described [5, 6, 7, 8].
In our study, mildly increased T1-weighted signal was evident in a tumor adjacent to the biceps tendonan appearance that has not, to our knowledge, been previously reported. This particular lesion also showed signal intensity greater than that of skeletal muscle on T2-weighted images and had peripheral enhancement. These imaging findings correlated microscopically to dense hyalinized fibrocollagenous tissue with widely separated fibroblasts that were small and spindly, and increased capillary vascularity near the lesion surface that was frayed and contained some fibrin deposition. The latter findings likely account for the peripheral enhancement.
Fibroma of the tendon sheath is most often confused with giant cell tumor of the tendon sheath at clinical examination and even at gross pathology. Both lesions occur in similar locations, although giant cell tumor is more common (2.7:1) [3]. Both lesions are more common in the upper extremities (86% vs 68% for fibroma of the tendon sheath and giant cell tumor of the tendon sheath, respectively). However, fibroma of the tendon sheath occurs in the lower extremities much less often than does giant cell tumor of the tendon sheath. When compared with giant cell tumor of the tendon sheath, fibroma of the tendon sheath usually occurs in a slightly younger population (35.1 years vs 39.2 years) and has a stronger predilection to occur in men (fibroma of the tendon sheath is 1.8-3.0 times more common in men than in women) [3]. Five of the six patients in our study were women, which does not correspond to the published demographic data, likely reflecting the small number of patients in our study.
Microscopically, the two tumors have separate and distinct histologic features. Fibroma of the tendon sheath is hypocellular, with slit-like vascular channels within a dense collagen matrix (Figs. 2A, 2B, 2C and 2D), whereas giant cell tumor of the tendon sheath is much more cellular and contains multiple multinucleated giant cells, foamy histiocytes, and hemosiderin [9, 10].
In fibroma of the tendon sheath, findings on standard radiographic imaging are often normal or may show a soft-tissue mass. Erosion or scalloping of the adjacent bone due to pressure erosion from the tumor has been reported but is infrequent [2, 11, 12]. Mild scalloping of the cortex from the tumor was evident in one patient in our series (Figs. 2A, 2B, 2C and 2D). Erosion of bone by giant cell tumor of the tendon sheath is recognized in as many as 15% of patients; this finding adds to the difficulty of differentiating between the two entities [13].
To date, only isolated case reports have been published that detail the MR imaging appearance of fibroma of the tendon sheath [4, 5, 6, 7, 8, 14]. Many of these reports are in publications other than imaging journals and therefore have limited descriptions and illustrations of the imaging findings. A review of these reports reveals a similar spectrum to that of our cases, although more variable signal was noted on T2-weighted images in our study, with areas of high signal intensity correlating to myxoid change histologically. Contrast enhancement in three cases from the literature varied from none, to mild, to marked [4, 7, 8].
When the findings in our six cases are combined with those of the previously reported six cases [4, 5, 6, 7, 8, 14], some conclusions about fibroma of the tendon sheath are evident. The imaging features of this lesion overlap with those reported for giant cell tumor of the tendon sheath. The diagnosis of fibroma of the tendon sheath can be suggested when MR imaging reveals a focal nodular mass adjacent to a tendon sheath with decreased signal on all pulse sequences and little or no enhancementan appearance that was seen in two (33%) of our patients. The MR imaging findings vary when areas of increased cellularity or myxoid change occur within the lesion. In these instances, differentiation of fibroma of the tendon sheath from other tumors, such as giant cell tumor of the tendon sheath, is problematic.
Limitations of our review include the small size of the study group and the limitations inherent in a retrospective study. Additionally, the absence of unenhanced fat-suppressed images in all patients would make it difficult to exclude minimal amounts of enhancement.
In summary, the diagnosis of fibroma of the tendon sheath is favored when the lesion is in a young to middle-aged individual, is located in an upper extremity adjacent to a tendon, is firm to palpation, and is painless, and when MR imaging shows a focal nodular mass with decreased signal on all pulse sequences and little or no enhancement.
Acknowledgments
We thank John S. Walsh, of the Department of Dermatology, Mayo Clinic,
Jacksonville, FL, for his assistance in reviewing the microscopic
specimens.
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