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Clinical Observations |
1 Department of Radiology, Memorial Sloan-Kettering Cancer Center, 1275 York
Ave., New York, NY 10021.
2 Present address: Department of Radiology, Potomac Hospital, Woodbridge,
VA.
3 Weill Medical College of Cornell University, New York, NY.
4 Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York,
NY.
5 Division of Orthopaedic Surgery, Memorial Sloan-Kettering Cancer Center, New
York, NY.
6 Department of Surgery, Memorial Sloan-Kettering Cancer Center, New York,
NY.
Received June 30, 2005;
accepted after revision September 13, 2005.
Address correspondence to D. M. Panicek
(panicekd{at}mskcc.org).
Abstract
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CONCLUSION. Unlike in most other histologic types of low-grade soft-tissue sarcoma, recurrent low-grade myxofibrosarcoma often is infiltrative; shows a tapering, tail-like margin and superficial spreading configuration; and metastasizes to various distant sites, including lungs, pleura, bone, adrenal gland, soft tissue, and mesentery. Knowledge of these unusual characteristics is important in assessing the presence and extent of recurrent low-grade myxofibrosarcoma before surgical reexcision.
Keywords: musculoskeletal imaging • myxofibrosarcoma • oncologic imaging • sarcoma
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Myxofibrosarcoma is one of the most common fibroblastic sarcomas seen in the extremities of elderly patients [2, 4-6]. Clinically, the primary lesion may present as a predominantly deep or subcutaneous multinodular growth; it also may involve the dermal layer and present as a cutaneous lesion [3]. The infiltrative growth pattern of low-grade myxofibrosarcoma can result in anatomically deceptive boundaries at surgery because of microscopic extension into the dermis and skeletal muscles [3, 6]. A completely infiltrative growth pattern along fascial planes without the formation of a discrete nodular lesion has been described in some cases [2, 7]. Given the various clinical and histopathologic appearances of this tumor, the potential for diagnostic and staging errors for recurrent low-grade myxofibrosarcoma is great if one assesses only for the masslike morphology that is typical of other recurrent lowgrade sarcomas.
To our knowledge, the imaging features of recurrent low-grade myxofibrosarcoma have not been reported. We undertook this study to define and illustrate the CT and MRI features of recurrent low-grade myxofibrosarcoma to alert others about the difficulties that exist in assessing the presence and extent of recurrent tumor before surgical reexcision.
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Twenty-five patients were excluded from further analysis because no MR or CT images were available for review. Fourteen additional patients were excluded due to lack of recurrent tumor. In the 10 remaining patients (seven men, three women; mean age at diagnosis, 54.6 years; range, 25-72 years), eight (80%) underwent MRI, including with gadolinium-enhanced sequences in five patients, of the largest recurrence; six (60%) underwent CT, including with IV contrast material in five patients; and six underwent MRI or CT but not both. The images showed recurrent low-grade myxofibrosarcoma that also was proven at histopathologic examination. Because of the retrospective nature of this study, nonuniform imaging protocols were used. All 10 patients underwent clinical and imaging follow-up at our institution.
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Medical records and imaging reports were reviewed for the presence and location of distant metastases and for the location of the initial primary tumor.
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At imaging, the largest recurrences were masslike (Fig. 1A) in four patients (40%), were multinodular (Fig. 1B) in two (20%), and had a superficial spreading configuration (Fig. 2A, 2B) in one (10%); recurrences had both masslike and multinodular configurations in three patients. Tumor margins were well defined (Fig. 1A) in four patients (40%). In six patients (60%), the largest recurrence showed more than one type of margin: tail-like and infiltrative in three (30%), tail-like and well-defined (Figs. 1B and 2A, 2B) in two (20%); and tail-like, well-defined, and infiltrative (Fig. 3) in one (10%). Perilesional edema pattern was seen in three patients (30%). Recurrent lesions invaded subjacent bone in two patients (Fig. 4).
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In two of the five patients who underwent contrast-enhanced CT, the largest recurrence enhanced more than muscle in the periphery of the lesion, but less than muscle in the center; in two other patients, the entire lesion enhanced more than muscle; and in the fifth patient, the lesion showed CT attenuation slightly less than that of muscle.
Transformation from low- to high-grade myxofibrosarcoma was seen in five patients (50%); in four, transformation occurred after three local recurrences and in one after two recurrences (mean, after 2.8 local recurrences). These patients all underwent surgical excision and external beam radiation or brachytherapy before and after recurrences. Four of the patients with transformation to high-grade sarcoma also developed metastases, and the fifth died of coexisting metastatic breast cancer. Amputation was required in two patients after multiple local recurrences.
Five patients (50%) had distant metastases in the lung (n = 3), the pleura (n =2) (Fig. 5A), an adrenal gland (n = 2) (Fig. 5A), bone (n = 1) (Fig. 5B), soft tissue (n =1), and mesentery (n = 1) (Figs. 5C, 5D, 5E); two patients had metastases in more than one location. The mean time to development of a metastatic lesion was 78 months (range, 48-132 months; median, 73 months). All five patients who developed metastasis eventually died. Two patients also had other primary tumors: metastatic breast cancer and squamous cell cancer of the lip, respectively.
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Myxofibrosarcoma has a significant myxoid component and shows a large
variation in cellularity, nuclear pleomorphism, and mitotic activity
[1,
2,
4]. A report from the Armed
Forces Institute of Pathology stated that 
50% myxoid areas are required
to define low-grade myxofibrosarcoma
[1], whereas Mentzel et al.
[2] suggested 10% as the
threshold. Even with ongoing improvements in the clinicopathologic definition
of myxoid tumors, considerable overlap and confusion persist regarding their
categorization [1,
6]. Confusion also may occur
because there are various other soft-tissue tumors with similar-sounding
names, such as low-grade fibromyxoid sarcoma
[8].
Myxofibrosarcoma has an indolent course and recurs in 55-63% of patients [1, 2, 5, 6]. The rate of local recurrence appears to be independent of the histologic grade and depth of tumor invasion [2, 6]. Myxofibrosarcoma has the unusual characteristic of extending along fascial planes well beyond the epicenter of the primary tumor [1, 6], at least partly accounting for its propensity for multiple recurrences.
In our series, there were 33 recurrences in 10 patients, with a median of 3.3 recurrences per patient. Myxofibrosarcoma tends to become progressively higher in grade at recurrence; therefore, even low-grade myxofibrosarcoma must be diligently followed with meticulous clinical and radiologic evaluations for local recurrence [2, 6]. Transformation to high-grade sarcoma was seen in five (50%) of our patients, all after other recurrences. Mentzel and colleagues [2] reported that higher patient mortality is observed when recurrences occur within 12 months of the original resection.
Metastases are rare in most low-grade softtissue sarcomas [1, 9]. Metastases are more common in higher-grade tumors, large tumors (> 10 cm), and deep-seated neoplasms [1]. Earlier descriptions of myxofibrosarcoma stated that low-grade myxofibrosarcoma did not tend to metastasize [2, 4], but Huang et al. [6] subsequently reported that low-grade myxofibrosarcoma metastasized distantly in 16.3% of cases. As low-grade myxofibrosarcoma recurs and progresses to higher grade, reports of the rate of distant metastasis have been as high as 23% [2].
In our 10 patients with locally recurrent low-grade myxofibrosarcoma, half developed distant metastases—in all but one case after multiple local recurrences. In those five patients, low-grade myxofibrosarcoma had recurred as high-grade sarcoma, and all patients developed metastases after multiple local recurrences and died; metastases occurred not only in lung, as expected for softtissue sarcomas, but also in pleura, adrenal gland, mesentery, soft tissue, and bone. Reported common sites of metastases across all tumor grades are lung, regional lymph nodes, pleura, and bone [1, 2, 4, 6].
Low-grade myxofibrosarcoma is of low attenuation on CT and shows low to intermediate signal on T1-weighted MR images. The solid and myxomatous components both show high signal on T2-weighted MR images, with the myxoid component showing higher signal intensity similar to that of fluid. Nodular and peripheral enhancement is often seen in the solid components. At MRI and CT, low-grade myxofibrosarcoma may closely resemble other myxoid tumors, such as myxoma, myxoid liposarcoma, and myxoinflammatory fibroblastic sarcoma [10].
One case report described a myxofibrosarcoma that infiltrated throughout the thigh without formation of a discrete tumor nodule [7]. Superficial and infiltrative tumor may be mistaken for inflammatory processes such as fasciitis [1, 7]. This spreading pattern presents a diagnostic dilemma, given that imaging evaluation for primary and recurrent tumor typically consists of identifying discrete masses that disrupt normal muscle architecture [11, 12]. Assessment for tumor recurrence is further confounded by the superimposed radiation and postsurgical changes typically present in patients with low-grade myxofibrosarcoma. All 10 patients in our study had undergone surgery and had received radiation treatment before imaging of recurrent lowgrade myxofibrosarcoma; it was not possible to determine whether perilesional edema, when present, was due to treatment effects, the recurrent tumor itself, or both.
Another lesion that can mimic the spreading pattern of low-grade myxofibrosarcoma is nodular fasciitis, a benign proliferation of fibroblasts that may spread along superficial fascial planes [13]. Also, myxoinflammatory fibroblastic sarcoma, a primarily nodular, low-grade myxoid tumor, may extend in a sheetlike pattern along a tendon sheath [10].
Other types of soft-tissue sarcomas can show an apparent pseudocapsule at imaging, thereby giving the misleading impression that the lesion is well localized despite the presence of infiltrative tendrils at pathologic examination. Recurrent low-grade myxofibrosarcoma appears to have a particular propensity for tail-like or infiltrative growth. Although many of the recurrences we encountered had a typical nodular or multinodular appearance, 60% had tail-like margins extending from the tumor nodule and 40% had infiltrative and poorly defined margins.
Given the infiltrating tendency of recurrent low-grade myxofibrosarcoma, the full extent of the tumor along fascial planes may be difficult to determine or may be overlooked. Meticulous imaging evaluation with particular attention to tail-like extensions is mandatory for surgical planning. If the radiologic description of the tumor is limited to the nodule and surgery is planned based on that information, the resection margins may be inadequate and recurrence imminent. The high rate of recurrence and further conversion to higher grade sarcoma put the patient at risk for metastases and death.
Invasion of subjacent bone by soft-tissue sarcomas is relatively uncommon in the absence of prior fracture or periosteal disruption, but occurred in 20% of our patients. This finding underscores that recurrent low-grade myxofibrosarcoma is an unusually aggressive tumor.
This retrospective study has limitations. The number of patients with recurrent lowgrade myxofibrosarcoma for whom imaging was available was relatively small. Given that the patients were referred to our tertiary care cancer center, the patient population may have been skewed toward more complicated or atypical presentations. Low-grade myxofibrosarcoma that recurred may have represented more aggressive or atypical low-grade myxofibrosarcoma. If the initial pathologic diagnosis of low-grade myxofibrosarcoma was nonrepresentative because of sampling error, tumor recurrence may have been due to a (nonsampled) portion of the tumor that was of a higher grade. The imaging studies were performed with a variety of protocols, but those variations would not be expected to affect the observed patterns of recurrence.
Radiologists evaluating patients with previously resected low-grade myxofibrosarcoma need to be aware of the variable patterns of growth and appearances of recurrent lowgrade myxofibrosarcoma on imaging studies. A tapering tail of enhancing tumor extending from a nodular recurrence, consistent with spread along fascial planes, may be seen in as many as 60% of cases; diligent evaluation and explicit communication of the farthest extent of such tails are required to help the surgeon achieve clean surgical margins at resection. Tumor margins were infiltrative and poorly defined in 40% of our patients, which likely also contributed to local recurrence. Finally, the fact that recurrent low-grade myxofibrosarcoma often is associated with distant metastases, including in locations atypical for other soft-tissue sarcomas, should be taken into account when planning follow-up imaging strategies.
Acknowledgments
We thank Carolina Montalvo for her dedicated assistance.
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