AJR 2002; 178:989-993
© American Roentgen Ray Society
Dermatofibrosarcoma Protuberans
MR Imaging Features
William C. Torreggiani1,
Khalid Al-Ismail1,
Peter L. Munk1,
Savvas Nicolaou1,
John X. O'Connell2 and
Margaret A. Knowling3
1
Department of Radiology, Vancouver General Hospital, University of British
Columbia, 899 W. 12th Ave., Vancouver, B. C., V5Z 1M9 Canada.
2
Department of Pathology, Vancouver General Hospital, University of British
Columbia, Vancouver, B. C., V5Z 1M9 Canada.
3
Department of Oncology, British Columbia Cancer Agency, 600 W. 10th Ave.,
Vancouver, B. C., V5Z 4E6 Canada.
Received January 17, 2001;
accepted after revision September 28, 2001.
Presented at the annual meeting of the American Roentgen Ray Society,
Seattle, April-May 2001.
Address correspondence to P. L. Munk.
Abstract
OBJECTIVE. The objective of our study was to describe the MR imaging
features of 10 cases of histologically confirmed dermatofibrosarcoma
protuberans.
CONCLUSION. MR imaging is useful in identifying the extent and
location of dermatofibrosarcoma protuberans. Although most cases of this tumor
are superficial and well defined, we have shown three cases in which the tumor
was in a deep location and one case in which the tumor was ill defined in
appearance. Knowledge of the variable MR imaging appearances of these tumors
may aid in the diagnosis of difficult or atypical cases.
Introduction
Dermatofibrosarcoma protuberans is an uncommon spindle cell tumor, which
was originally described as a distinct clinicopathologic entity in 1924 by
Darier and Ferrand [1]. The
term "dermatofibrosarcoma protuberans" was coined by Hoffman
[2] in 1925 and, to this day,
remains the preferred name among many proposed for this lesion.
Dermatofibrosarcoma protuberans typically arises in the dermis as a
multinodular mass, which then spreads into the subcutaneous tissues and muscle
[3,4,5].
Males are slightly more commonly affected than females. The tumor occurs in
patients of all ages, with the highest frequency occurring between the second
and the fifth decades [6].
Lesions ranging from 1 cm to more than 25 cm have been described in the
literature [7]. The trunk is
the most common site of involvement for dermatofibrosarcoma protuberans,
accounting for almost half of all cases
[4,
8,
9]. The extremities followed by
the head and neck are the next most common sites, but tumors may occur on any
part of the body [10].
Patients often ignore these tumors because of their slow growth. In our
experience, they are often left untreated for many years. Dermatofibrosarcoma
protuberans has an excellent prognosis after complete resection but has a
marked tendency to recur locally if inadequate surgical resection margins are
obtained. Metastases, however, are rare
[10].
MR imaging is not routinely performed as part of the workup of patients
with these neoplasms because of their typical clinical appearance and
superficial location. When MR imaging is used, it is often to evaluate larger
or atypical primary lesions or recurrent disease. Kransdorf and Meis-Kindblom
[3] reported the MR imaging
appearances in four of 11 cases of histologically proven dermatofibrosarcoma
protuberans. To our knowledge, ours is the largest series of these tumors
assessed with MR imaging in the literature. We report the MR imaging findings
of 10 patients with histologically proven dermatofibrosarcoma protuberans with
emphasis on the MR imaging features that characterize this tumor.
Materials and Methods
We retrospectively analyzed the soft-tissue tumor registry of all patients
with dermatofibrosarcoma protuberans in our institution since 1989. This date
reflected the introduction of MR imaging for the evaluation of soft-tissue
tumors in our practice. All cases had histologic proof of this tumor by either
surgical excision or by percutaneous biopsy. Sixty-nine patients were found.
Of these, MR imaging was performed in 12 patients, but in two patients, it was
not possible to retrieve the images. Imaging was performed on a 1.5-T unit
(Signa; General Electric Medical Systems, Milwaukee, WI). T1-weighted (TR
range/TE range, 415-800/9-24) and either standard spin-echo T2-weighted or
fast spin-echo T2-weighted (TR range/TEeff range,
2,000-6,000/61-90) MR imaging was performed in all cases. Short tau inversion
recovery (STIR) sequences (TR range/TE range, 2,000-2,600/13-30; inversion
time, 150 msec) were performed in seven of the 10 cases. IV gadolinium
(Magnevist; Berlex Canada, Pointe Claire, Canada) was given in three cases at
a dose of 0.1 mmol/kg. Fat suppression was not used as part of either standard
T2-weighted or fast spin-echo T2-weighted sequences in any of the 10 patients.
A standardized protocol was lacking because the imaging was performed over an
11-year period during which imaging protocols varied. Images from the 10
available cases were submitted to two radiologists experienced in
musculoskeletal imaging for review. The radiologists were required to obtain
data on the signal appearances on T1-weighted, T2-weighted, or fast spin-echo
T2-weighted and STIR images as well as on whether enhancement was present
after gadolinium administration. Signal characteristics were compared with
those of muscle, fat, and water. Radiologists were also asked to assess size,
location, and depth from the skin to the deepest margin of the lesion. Lesions
were also broadly categorized as belonging to two groups: superficial and
deep. A lesion was considered deep when it was clearly seen to penetrate or
lie deep relative to the superficial fascia. In addition, the reviewers were
also asked to assess if the margins of the lesion were well defined or ill
defined. All data were obtained by consensus agreement.
Results
The patients included six men and four women (range, 33-60 years old; mean,
41 years). Seven patients had a primary lesion. In three patients, MR imaging
was performed to evaluate recurrent disease. Two cases involved the thigh, two
cases involved the shoulder, two cases involved the back, and one case each
involved the foot, the neck, the chest, and the forearm
(Table 1). The tumor was
considered exclusively superficial in seven cases. In three cases, it involved
a deep location. In one of these three cases, the tumor was in a deep location
because of extension from the subcutaneous compartment across the superficial
fascia. In a second case, although the tumor lay in a deep location in the
vastus lateralis, we were uncertain if this location was primary or an
extension from a superficial location (Fig.
1A,1B).
In the third case, the tumor was exclusively located deep in the chest wall
(Fig.
2A,2B).
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Fig. 1A. —43-year-old woman with 8-cm mass involving lateral aspect of
right thigh. Tumor had grown gradually over many years. Coronal T1-weighted MR
image (TR/TE, 550/16) shows 8-cm mass (arrow) of low signal intensity
that involves vastus lateralis, rectus femoris, and lateral part of vastus
intermedius.
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Fig. 1B. —43-year-old woman with 8-cm mass involving lateral aspect of
right thigh. Tumor had grown gradually over many years. Axial fast spin-echo
T2-weighted MR image (TR/TEeff, 4,000/80) shows mass to have
heterogeneous areas of both intermediate and high signal intensities.
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Fig. 2A. —35-year-old man with unusually deep dermatofibrosarcoma
protuberans. Coronal T1-weighted spin-echo MR image (TR/TE, 800/16) shows 4-cm
well-defined mass of slightly higher signal to muscle deep in right chest wall
protruding between ribs.
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Fig. 2B. —35-year-old man with unusually deep dermatofibrosarcoma
protuberans. Coronal short tau inversion recovery image (2,000/16; inversion
time, 150 msec) shows mass of uniform high signal.
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In nine patients, measurements were made from the skin surface to the
deepest margin of the lesion. In one patient, because of the location of the
lesion in the chest wall, measurements were not feasible. In the other nine
patients, the distance from the skin to the deep margin of the tumor ranged
from 8 to 60 mm. The mean depth was 17 mm. In four patients, the lesion
clearly bulged into the skin surface (Fig.
3A,3B).
In the one case that involved the thigh, two small satellite lesions were
identified adjacent to the main lesion (Fig.
4A,4B).
The tumor was well defined in nine patients and ill defined in one. Tumor size
ranged from 2 to 8 cm with a mean size of 4 cm.
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Fig. 3A. —44-year-old man with recurrent dermatofibrosarcoma of
shoulder. Sagittal T1-weighted spin-echo image (TR/TE, 800/24) shows 3.5-cm
mass (arrow) at site of previous resection. Mass is of slightly
higher signal than that of adjacent muscle and protrudes through skin.
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Fig. 4A. —39-year-old woman with anteriorly located superficial mass in
thigh. Axial T1-weighted image (TR/TE, 800/18) shows 4.5-cm well-defined mass
of uniform signal, similar to that of adjacent muscle (straight
arrow). Note two small satellite lesions (curved arrows).
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Fig. 4B. —39-year-old woman with anteriorly located superficial mass in
thigh. Axial fast spin-echo T2-weighted image (TR/TEeff, 6,000/84)
shows principal lesion of intermediate signal, similar to that in adjacent
fat.
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All 10 patients underwent conventional T1-weighted imaging, on which the
tumor was isointense to skeletal muscle in five patients and slightly
hypointense to skeletal muscle in three patients. In two patients, the tumor
was of higher signal than that of skeletal muscle. In all 10 patients, the
tumor was of lower signal than that of subcutaneous fat on T1-weighted
imaging. T2-weighted imaging was performed in all 10 patients. In six
patients, conventional spin-echo T2-weighted imaging was used, and fast
spin-echo T2-weighted imaging was used in the remaining four. Compared with
that of fat, the tumor was of predominantly high signal on T2-weighted or fast
spin-echo T2-weighted sequences in five patients and of intermediate signal
(i.e., similar to that of fat) in five patients. In two patients, it was
difficult to identify the lesion on conventional T2-weighted sequences because
the signal characteristics were similar to those of the subcutaneous fat in
which the lesions lay. Seven patients underwent STIR imaging. The tumor was of
high signal, similar to that of water or blood vessels in all patients. IV
gadolinium enhancement was used in three patients. In two of these patients,
there was uniform enhancement of the entire tumor. In one patient, there was
patchy central enhancement (Fig.
5A,5B,5C).
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Fig. 5A. —45-year-old man with recurrent dermatofibrosarcoma
protuberans of superficial portion of back. Axial T1-weighted image (TR/TE,
800/16) shows 2.5-cm mass (arrow) of uniform signal, similar to that
in adjacent muscle.
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Fig. 5B. —45-year-old man with recurrent dermatofibrosarcoma
protuberans of superficial portion of back. Axial T1-weighted image (800/16)
after gadolinium infusion shows patchy central enhancement of mass
(arrow).
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Fig. 5C. —45-year-old man with recurrent dermatofibrosarcoma
protuberans of superficial portion of back. Axial short tau inversion recovery
sequence (2,000/16; inversion time, 150 msec) shows well-defined mass of high
signal.
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Discussion
MR imaging is invaluable in the evaluation of soft-tissue tumors
[11], allowing accurate
localization before surgery. Galant et al.
[12] reported on the use of MR
imaging in the evaluation of the location of subcutaneous soft-tissue masses
relative to the superficial fascia. They found that if a subcutaneous lesion
crossed the superficial fascia, malignancy was 6.88 times greater than that
for lesions that did not cross the fascia. However, their group of 64 patients
did not include any cases of dermatofibrosarcoma protuberans.
The series by Kransdorf and Meis-Kindblom
[3] was the largest to use MR
imaging to identify dermatofibrosarcoma protuberans tumors. In their 1994
series, Kransdorf and Meis-Kindblom described four patients, of a total of 11
patients scanned in their series, who underwent MR imaging. The tumors in all
four cases described in their series were well-defined lesions on MR imaging
with low signal on T1-weighted images and signal higher than fat on
T2-weighted sequences. The tumor in one case had areas of high signal on
T1-weighted sequences compatible with that of hemorrhage. Our series included
10 patients who underwent MR imaging as part of the evaluation of their tumor.
Whereas our cases share some similar imaging features to the findings of
Kransdorf and Meis-Kindblom, there were several important differences.
Although all the lesions described in their article were located
superficially, we have shown three cases in which the location of the tumor
was deep, either because of its large size with deep extension or because the
tumor was primarily deep. Our series also included one case in which the tumor
was poorly defined with a markedly irregular deep margin. We also have shown
that all lesions that underwent STIR imaging and those of patients who were
given IV gadolinium showed high signal and enhancement of lesions,
respectively. In an additional two cases, on conventional T2-weighted
sequences, it was difficult to visualize the tumor because it was of similar
signal to that of the subcutaneous fat in which it lay. In both of these
cases, STIR sequences with an inversion time of 150 msec provided fat
suppression allowing clear definition of the tumor. In our institution, we do
not routinely use fat suppression with T2-weighting in imaging of soft-tissue
tumor. Such a sequence, if used, would likely have effectively shown these two
tumors.
Our usual imaging protocol for these patients includes three sequences:
T1-weighted and T2-weighted spin-echo or fast spin-echo and STIR. Presumably,
fast-saturation spin-echo or fast spin-echo could be used successfully as a
substitute for STIR. We do not believe that routine use of gadolinium is
indicated. We select a plane perpendicular to the long axis of the body part
being examined.
Several of the tumors in our series were atypical, and it might be argued
that we have not given an accurate portrayal of the typical imaging features
of dermatofibrosarcoma protuberans. We would argue that it is these types of
atypical cases that will often be seen by radiologists. Imaging is usually not
requested in classical cases in which the tumors are usually small and
superficial, allowing accurate clinical diagnosis. Knowledge of the variable
range of MR imaging features of dermatofibrosarcoma protuberans is, therefore,
important.
In conclusion, dermatofibrosarcoma protuberans is a rare, usually
superficial soft-tissue sarcoma, which is often diagnosed by its typical
clinical manifestations. We have described the imaging findings of 10 cases of
histologically proven dermatofibrosarcoma protuberans. MR imaging allows
accurate preoperative assessment and aids in the diagnosis of atypical or
difficult cases.
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Abstract
Introduction
