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1243
Myositis
Ossificans:
MR Appearance Correlation
with Radiologic-Pathologic
Mark J. Kransdorf1’2 Jeanne M. Meis3 Jarnes S. Jelinek2’4
We reviewed retrospectively the MR images of eight histologically proved cases of myositis ossificans and correlated the MR appearance with the histologic findings, as well as with other radiologic studies. Patients with available MR images were chosen from a group of 326 cases in our radiologic archives of histologically proved and radiologically correlated myositis ossificans. In addition to MR images, all patients had plain radiographs, six had CT scans, and two had artenograms. On T2-weighted spinecho MR the lesions were relatively well defined and inhomogeneous and had intermediate to high signal intensity. The latter corresponded to a central proliferating core of fibroblasts and myofibroblasts with a myxold stroma resembling nodular fasciitis, rimmed by osteoblasts with bone production. Edema surrounded lesions less than a few months old. Ti-weighted images of early lesions were normal or showed evidence of a mass by displacement of fat planes. Hemorrhage and fluid-fluid levels were seen in one lesion of intermediate duration. Mature lesions tended to be well defined with inhomogeneous signal intensity, similar to that of fat, representing areas of fat situated between bone trabeculae within the lesion. We present the MR appearance of myositis ossificans and correlate it with other
radiologic
studies
and the histologic
has many
AJR i57:i243-1248,
Myositis
the Department of the Army, the Department of Defense, or the UnifOrmed Services University of the Health Sciences. I Department of Radiologic Pathology, Armed
Forces
Institute
of Pathology,
20306-6000. Address reprint Kransdorf. 2 Department of Radiology
one, Uniformed Sciences,
and
Services University
Bethesda,
3Oepartment Forces Institute 20306-6000.
Washington, DC requests to M. J. Nuclear
of the Health
MO 20814.
of Soft Tissue of Pathology,
Pathology, Armed Washington, DC
4Department of Radiology, Washington Center, Washington, DC 20010. 0361-803X/91/1
Medi-
576-1243
Hospital
appearance
of myositis
December
199i
is a benign, solitary, self-limiting, ossifying soft-tissue mass skeletal muscle. A history of trauma is often inapparent, and we make no distinction between lesions of atraumatic and traumatic origins. The pathogenesis of myositis ossificans is unknown, although the term myositis is a misnomer in that no primary inflammation of skeletal muscle is associated with the process [1]. Synonyms include pseudomalignant osseous tumor of soft tissue, typically
The opinions or 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 varying
relates
Knowledge
Received May 13, 1991 ; accepted after revision July23, 1991.
findings.
to the histologic changes that occur as the dIsorder progresses. of the MR appearance of myositis ossificans is important in that the lesion of the MR imaging characteristics frequently associated with malignancy.
ossificans
ossificans
occurring
extraosseous
within
localized
nonneoplastic
bone
and cartilage
formation,
myositis
ossi-
ficans circumscripta, pseudomalignant myositis ossificans, and heterotopic ossification [1-4]. We describe the MR appearance of eight lesions of histologically proved myositis ossificans
and correlate
Materials
and
these
findings
with other
radiologic
and histologic
studies.
Methods
The radiologic archives of the Armed Forces Institute of Pathology contain 326 cases of histologically proved and radiologically correlated myositis ossificans accumulated in consultation over 40 years. Through a retrospective review, we identified eight patients in whom MR images were available. The clinical histories and radiologic findings in these eight patients form the basis for this report. The study group consisted of five women and three men 1273 years old (mean, 32 years). The thigh was the most common location; it was involved in five cases. One case each occurred in the popliteal fossa, proximal upper arm, and proximal forearm.
Downloaded from www.ajronline.org by Grand Valley State University on 09/22/13 from IP address 148.61.13.133. Copyright ARRS. For personal use only; all rights reserved
1244
KRANSDORF
Fig. 1.-Early myositis ossificans in upper arm of A, Coronal 12-weighted SE MR image (2000/80) (arrow); others are obscured by diffuse surrounding subcutaneous f.t. B, Axial CT scan (bone window) shows incomplete apparent on radiograph (not shown). C, Digital subtraction arterlegram shows a diffuse
29-year-old woman. shows inhomogeneous edema
and adjacent
peripheral
curvilinear
All lesions
(except
one)
were
onal planes and were evaluated definition,
intensity
imaged
in at least
for the following
and homogeneity
two
features:
of the signal,
orthog-
margin
and presence
or
absence of surrounding edema. When edema was present it was graded as diffuse or focal and as mild, moderate, or extensive. In addition
to MR
scans,
intervention; was
images,
all patients
had
and two had arteriograms. the
1 -31
time
days
on duration
patient,
the lesion
histologically Hematoxylin
radiographs,
MR
imaging
six
had
were imaged
and
biopsy
CT
before
or resection
13
days). The clinical age of lesions was of symptoms in seven of eight cases. In one
(mean,
based
In all cases
between
plain
All lesions
was an incidental
the diagnosis
finding.
of myositis
ossificans
was verified [1 5-7].
according to criteria previously described and eosin-stained slides were reviewed without
,
previous
knowledge of each lesion’s duration, and the lesions were classified by the authors as early (recent), intermediate, or late (remote or fully mature) by using the following criteria. Early lesions consisted primanly
of a nonossified
and myofibroblasts, lamellar
bone
central
core
of proliferating
with a minor component
at the periphery;
part of endochondral
hyaline
calcification.
minor or no proliferating entirely of osteoid rimmed
benign
of osteoid
cartilage
Intermediate
could
be present
phenomenon,
lamellar
fibroblastic core; they consisted almost by active osteoblasts and were surrounded
bone.
The
circumscription,
presence
intralesional
or hemosiderin deposition, hematopoiesis, skeletal muscle, intralesional vasculature, sule formation, and edema or myxoid connective
tissue
was
as
lesions had either a
by a shell of mature lamellar bone. Late lesions consisted of mature
fibroblasts
and mature
assessed
exclusively
or absence
of a zoning
inflammation,
hemorrhage
entrapment or atrophy of perilesional fibrosis or capchange in the surrounding
also.
The pathologic features of each lesion were then correlated with the patient’s clinical history, MR images, and other radiologic images. One of these cases has been reported previously [2].
AL.
AJR:157,
mass in upper aspect of arm. Portions subcutaneous fat Edema extends along calcification
tumor blush, indistinguishable
MR examinations were performed with a variety of scanners. Scanning sequences included spin-echo (SE) Ti -weighted, 300-650/ 20-40 (TR/TE), and T2-weighted, 2000-3000/60-90, pulse soquences. In addition, one patient was evaluated with gadopentetate dimeglumine-enhanced MR and another with inversion-recovery MR imaging.
ET
December
of margin are relatively fascial planes separating
well defined muscle and
Edema seen on A is not evident. Mineralization
(arrow).
1991
was not
from that of a malignant neoplasm.
Results MR Findings In early
and
intermediate
lesions,
myositis
ossificans
ap-
peared on T2-weighted SE MR images as a moderately to markedly inhomogeneous soft-tissue mass with increased signal intensity and extensive diffuse surrounding edema. Curvilinear
and irregular
areas
of decreased
signal
intensity
were seen surrounding and coursing through all intermediate lesions and through one of three early lesions, giving these lesions relatively well-defined margins. The margins of two early lesions were difficult to separate from the surrounding edema. Findings on corresponding Ti -weighted images were normal, or showed evidence of a mass by displacement of fascial planes (Figs. 1 and 2). One patient with fluid-fluid levels had increased signal intensity in the muscle surrounding the lesion (Fig. 3). Imaging after administration of gadopentetate dimeglumine (Fig.
in one
2). Changes
patient
compatible
showed with
marked
marrow
enhancement
edema
were
also
detected within the shaft of the femur adjacent to one lesion in the mid thigh. Mature (late) lesions were well-defined inhomogeneous masses with a signal intensity approximating that of fat on both T2- and Ti -weighted images without associated edema. On all pulse sequences, a rim of decreased signal intensity surrounded the lesion and similar areas of decreased signal intensity were apparent within the lesion (Fig. 4).
Other
Radiologic
Findings
were available for review in six patients. The edema detected on MR images was not detected on CT scans. In one early case, however, mild edema was seen CT
scans
marked
in the subcutaneous
adipose
tissue
adjacent
to the
lesion.
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AJR:157,
December
MR
1991
IN
MYOSITIS
OSSIFICANS
1245
D
Fig. 2.-Early myositis ossificans in thigh of 24-year-old woman with pain for 3-4 weeks. A, Axial T2-weighted SE MR image (2800/80) shows inhomogeneous, relatively well-defined mass surrounded by diffuse edema in posterior aspect of thigh. Edema extends along fascial plane separating muscle from subcutaneous fat. B, corresponding axial TI-weightedSE MR image (400/20) shows mass is isointense with skeletal muscle. Area with signal Intensity similar to that of skeletal muscle extends Into subcutaneous fat laterally (arrow), matching area of Increased signal intensity (edema) on A. C, Axial TI-weighted SE MR image (400/20) obtaIned after IV gadopentetate dimeglumine at same level as A and B shows moderate Inhomogeneous enhancement. Edema is seen enhancing along fascial planes (arrow). 0, Lateral radiograph shows densely mineralized mass in posterior aspect of thigh. MineralIzed areas are prsent in A as curvilinear regions of decreased signal. E, Low-power photomicrograph in another patient with similar early lesion shows characteristic zoning phenomenon with central cellular region (asterisk) and peripheral new bone formation. Scattered areas of cartilage formation (arrows) are also seen. Note compressed atrophic skeletal muscle adjacent to right of lesion.
(H and E, original
magnification
x7.5)
Four cases had typical peripheral mineralization (Fig. 3), although it was irregularly shaped and somewhat convoluted in one case. In three ofthese cases, a narrow rim of decreased signal intensity could be seen retrospectively on MR scans. In an early lesion, the peripheral mineralization was incomplete and faint (Fig. i). One mature lesion that had been clinically
apparent
for several years had diffuse mineralization
Arteriography
showed
was available
a distinct
tumor
lesion was hypovascular. Radiographs were available
lesion, no mineralization
in two
blush
cases.
One early lesion
(Fig. 1). A second
in all eight
cases.
was seen, and in another
alization was vague. The remaining mineralized, more so peripherally,
(Fig. 4). mature
In one early
the miner-
early lesion was densely but the mineralization did
not demonstrate
a definite
bonelike
character.
A similar
ap-
pearance was seen in one intermediate lesion. Two intermediate lesions were densely mineralized, with a distinct bonelike character, and were more mature peripherally. One mature lesion was densely mineralized diffusely, and the other had the appearance
of heterotopic
ossification.
Periosteal
reaction
was detected adjacent to one intermediate lesion. In this case and one other, the mass was adjacent to but separate from bone. Histologic
Findings
Histologically,
three
three as intermediate,
cases
were
classified
as early lesions,
and two as late. The central proliferat-
KRANSDORF
1246
ET AL.
AJR:157, December1991
Fig.
3.-Myositis ossificans of intermediate of 31-year-old woman. A, Axial TI-weighted SE MR image (500/40) shows lesion with fluid-fluid levels adjacent to
age in forearm
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...
proximal radius. Areas of increased signal Intensity adjacent to lesion may be related to hemorrhage. B, CT scan (bone window) at level sImilar to that of A shows lesion’s dense peripheral mlnerallzatlon, less apparent on MR. Tissue attenuation within lesion is somewhat lower than that of surrounding soft tissue. C, Radiograph shows densely mineralized mass overlying proximal radius. Peripheral mmeralization Is seen better on CT (B). Retrospectlve review of radiograph obtaIned 45 days ear-
!
:
11crshowed no mineralization. D, Photomicrograph shows mature lamellar bone surrounding hemorrhagic cysts (asterisks). Regions between trabeculae consist of densely
packed fibroblasts and myofibroblasts with ocmultinucleated giant cells. (H and E, magnification x30)
casional original
ing fibroblastic and myofibroblastic core of tissue in intermediate lesions was extremely cellular and had nent myxoid stroma in some cases, resulting in resemblance to nodular fasciitis, both histologically ologically.
The
nodular
fasciitis-like
areas
merged
early and a promia strong and radiwith
de-
posits of osteoid that were rimmed by osteoblasts; these areas in turn were surrounded by a rim of mature lamellar bone at the periphery of the lesions. Five cases had a distinct zoning pattern in which lesional maturation progressed from central, nonossified cellular foci
to osteold to these was a ules. Another pattern and chondroosseous
peripheral rims of mature lamellar bone. One of multinodular lesion with zoning in multiple nodcase (a biopsy) did not show a typical zoning consisted of nodular fasciitis-like areas with nodules;
the other
two were
late lesions
muscle fibers were seen within lesions. As lesions matured, the nodular fasciitis-like areas in the intertrabecular spaces became areas of delicate fibrosis containing thin-walled ectatic
vascular
channels
that
eventually
became
replaced
by
both adipose tissue and dense fibrosis in the most mature lesions. In general, histologic stage correlated well with duration of symptoms, which usually were pain and/or soft-tissue mass. Early lesions were associated with 3-6 weeks of symptoms, intermediate
lesions
with
symptoms
and late lesions with symptoms
of 6-8
weeks’
duration,
of up to 10 years’ duration.
Discussion
and
were composed entirely of calcified, mature lamellar bone. Five cases had hyaline cartilage. One was a late lesion with a cartilaginous cap at the periphery; in the other four cases, the hyaline cartilage was associated with osteoid and undergoing endochondral calcification. All lesions were well circumscribed and rimmed by compressed fibrous connective tissue; most of these were surrounded by atrophic skeletal muscle, and, not infrequently, entrapped, atrophic skeletal
On MR imaging, myositis ossificans was most often a relatively well-defined, inhomogeneous soft-tissue mass. Diffuse surrounding edema was quite prominent in lesions imaged within 8 weeks of the onset of symptoms (Figs. 1 and pattern of diffuse edema has been described previously, as has edema in the adjacent bone marrow [2]. The time required for resolution of the surrounding edema could 2). This
not be determined;
however,
we speculate
that the edema
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AJR:157,
MR IN MYOSITIS
December1991
OSSIFICANS
i 247
Fig. 4.-Mature myositis ossificans in popliteal fossa of 35-year-old man. Mass had been present for several years. A, Axial T2-weighted SE MR image (2500/80) shows a well-defined inhomogeneous mass in popliteal fossa. Areas of increased signal within mass have about the same signal as subcutaneous fat. Similar findings were seen on TI-weighted image (not shown). B, Axial CT scan (bone window) at level similar to that of A shows irregular diffuse mineralization throughout mass. Attenuation coefficient of nonmineralized
area is diffIcult to assess, but may be similar to that of fat.
C, Photomicrograph
adipose
shows
mature
lamellar
bone
corresponding
to densely
mineralized
tissue and delicate fibrous connective tissue. (H and E, original magnification
could persist for several association with mature MR images showed
months. Edema lesions. curvilinear and
was not detected
in
portions
of mass.
Regions
between
trabeculae
consist
of
x30)
The CT appearance of myositis ossificans has been well [1 0-i 3]. CT usually will show a rim of mineralization around lesions after 4-6 weeks. Even when densely mineralized on CT, this rim is much less apparent on MR. The described
irregular
regions
of
decreased signal intensity peripherally as well as within lesions, corresponding to mineralization seen on CT scans and
center
of the mass
may have decreased
CT tissue
attenuation
MR and was often best appreciated retrospectively (Figs. 2 and 3). It was not seen on MR in two early cases in which radiographs were normal or showed only faint mineralization.
[1 0, 13], again reflecting its similarity to nodular fasciitis [8], and corresponding to areas of increased signal intensity on T2-weighted SE MR imaging. Mature lesions may show diffuse ossification (Fig. 4), with corresponding regions of de-
This mineralization
creased
radiographs.
As expected,
this was
delineated
much
less apparent
the lesion from
on
the surrounding
edema or tissue in all but two early cases. The areas of increased signal intensity seen centrally within the early lesions on T2-weighted images are probably related to the extremely cellular central areas of proliferating fibro-
blasts and myofibroblasts within a myxoid stroma or extracellular matrix. These areas are histologically and radiologically similar in appearance to nodular fasciitis [8]. Areas of hyaline cartilage also may contribute to this appearance. The fluid-fluid levels detected in one case (Fig. 3) are consistent
with previous
hemorrhage
[9], which
is not an uncommon
finding in the inner, most immature portion of the lesion. Fluidfluid levels are a nonspecific finding and have been reported in other soft-tissue lesions including synovial sarcoma and
hemangioma [9]. The areas of intermediate signal seen within late myositis ossificans on T2-weighted images reflect areas of fatty infiltration
same
between
areas
bone
trabeculae
have a high signal
within
intensity
the
lesion.
These
on Ti -weighted
on all MR pulse
at least in part, for the contrast
out associated
edema,
ment. Plain radiographs
sequences.
enhancement
identified
within
and we would
in myositis
ossificans
expect
no enhance-
show faint calcifi-
cation within 2-6 weeks after onset of symptoms [1 ]. A sharply circumscribed mass is usually apparent by 6-8 weeks
(although
it may be seen much earlier), becoming
smaller and
mature by 5-6 months [i3, i7, 18]. Although a discussion of the ability to reliably discriminate between benign and malignant lesions on the basis of MR
imaging spectrum
creased
quently
on both pulse sequences.
intensity
the lesion on MR [1 5]. Surrounding enhancement reflects associated edema [1 6]. Mature myositis will be avascular, reflecting the angiographic findings of normal bone [i 4], with-
images. The areas of decreased signal intensity on both pulse sequences represent the bone trabeculae of the lesion itself (Fig. 4). Areas of hemosiderin deposition from previous hemorrhage and fibrosis also may contribute to areas of de-
signal intensity
signal
In the active phase of myositis ossificans, arteriography shows a diffuse tumor blush and fine neovascularity [14]. Although understanding of gadopentetate-dimeglumine enhancement is incomplete, this vascularity is likely responsible,
alone is clearly beyond of MR appearances
the scope of this article, in myositis
ossificans
serves
the to
underscore the nonspecificity of MR imaging in many circumstances. Myositis ossificans, particularly in its early and intermediate phases, displays MR imaging characteristics freequated
with
malignancy.
KRANSDORF
1248
REFERENCES
Downloaded from www.ajronline.org by Grand Valley State University on 09/22/13 from IP address 148.61.13.133. Copyright ARRS. For personal use only; all rights reserved
1 . Ackerman
formation
LV. Extra-osseous
localized
(so.called
ossificans).
40-A:279-298 2. Hanna SL, Magill
myositis HL, Brooks
Case of the day. Pediatric. 3. 4.
5.
6. 7.
8.
MT,
non-neoplastic bone and cartilage J Bone Joint Surg (Am] 1958;
Burton
Myositis
EM,
ossificans
Boulden
TF,
Seidel FG. circumscripta. Radio-
Graphics I990;10:945-949 Heinrich SD, Zembo MM, MacEwen GD. Pseudomalignant myositis ossificans. Orthopedics 1989;12:599-602 Ogilvie-Harns DJ, Fomasier VL. Pseudomalignant myositis ossificans: heterotopic new-bone formation without a history of trauma. J Bone Joint Surg (Am) 1980;62-A: 1274-1283 Spjut Ri, Dorfman HD, Fechner RE, Ackerman LV. Tumors of bone and cartilage: atlas of tumor pathology, 2nd series fasc 5. Washington, DC: Armed Forces Institute of Pathology, 1971:412-423 Johnson LC. Histogenesis of myositis ossificans. Am J Pathol i948;24:681-682 Angervall L, Stoner B, Stener I, Ahren C. Pseudo-malignant osseous tumor of soft tissue: a dinical, radiological, and pathological study of five cases. J Bone Joint Surg (Br) 1969;51-B:654-663 Meyer CA, Kransdort MJ, Jelinek JS, Moser RP. Radiologic appearance of nodular fasciitis with emphasis on MR and CT. J Comput Assist Tomogr 199I;15:276-279
ET AL.
AJR:157,
December
1991
9. Tsai JC, Dalinka MK, Fallon MD, Zlatkin MB, Kressel HY. Fluid-fluid level: a nonspecific finding in tumors of bone and soft tissue. Radiology 1990;175:779-782 10. Amendola MA, Glazer GM, Agha FP, Francis IR, Weatherbee L, Martel W. Myositis ossificans circumscnpta: computed tomographic diagnosis. Radiology 1983;149:775-779 1 1 . Heiken JP, Lee JKT, Smathers AL, Totty WG, Murphy WA. CT of benign soft-tissue masses of the extremities. AJR 1984;142:575-580 12. Zeanah WR, Hudson TM. Myositis ossifican: radiologic evaluation of two cases with diagnostic computed tomograms. Clin Orthop 1982;168:
187-1 92 13. Hudson TM. Radiologic-pathologic correlation of musculoskeletal lesions. Baltimore: Williams & Wilkins, 1987:589-604 14. Yaghmal I. Myositis ossificans: diagnostic value of artenography. AJR I977;128:81 1-816
15. Pettersson
H, Eliasson J, Egund N, et al. Gadolinium-DTPA
enhancement
of soft tissue tumors in magnetic resonance imaging-preliminary clinical experience in five patients. SkeletalRadiol 1988;17:319-323 16. Erlemann A, Aeiser MF, Peters PE, et al. Musculoskeletal neoplasms: static and dynamic Gd-DTPA-enhanced MR imaging. Radiology 1989;171 :767-773 17. Norman A, Dorfman HP. Juxtacortical circumscribed myositis ossificans: evolution and radiographic features. Radiology 1979;96:301-306 1 8. Goldman AB. Myositis ossificans circumscripta: a benign lesion with a malignant differentialdiagnosis. AJR 1976;126:32-40
1243
Myositis
Ossificans:
MR Appearance Correlation
with Radiologic-Pathologic
Mark J. Kransdorf1’2 Jeanne M. Meis3 Jarnes S. Jelinek2’4
We reviewed retrospectively the MR images of eight histologically proved cases of myositis ossificans and correlated the MR appearance with the histologic findings, as well as with other radiologic studies. Patients with available MR images were chosen from a group of 326 cases in our radiologic archives of histologically proved and radiologically correlated myositis ossificans. In addition to MR images, all patients had plain radiographs, six had CT scans, and two had artenograms. On T2-weighted spinecho MR the lesions were relatively well defined and inhomogeneous and had intermediate to high signal intensity. The latter corresponded to a central proliferating core of fibroblasts and myofibroblasts with a myxold stroma resembling nodular fasciitis, rimmed by osteoblasts with bone production. Edema surrounded lesions less than a few months old. Ti-weighted images of early lesions were normal or showed evidence of a mass by displacement of fat planes. Hemorrhage and fluid-fluid levels were seen in one lesion of intermediate duration. Mature lesions tended to be well defined with inhomogeneous signal intensity, similar to that of fat, representing areas of fat situated between bone trabeculae within the lesion. We present the MR appearance of myositis ossificans and correlate it with other
radiologic
studies
and the histologic
has many
AJR i57:i243-1248,
Myositis
the Department of the Army, the Department of Defense, or the UnifOrmed Services University of the Health Sciences. I Department of Radiologic Pathology, Armed
Forces
Institute
of Pathology,
20306-6000. Address reprint Kransdorf. 2 Department of Radiology
one, Uniformed Sciences,
and
Services University
Bethesda,
3Oepartment Forces Institute 20306-6000.
Washington, DC requests to M. J. Nuclear
of the Health
MO 20814.
of Soft Tissue of Pathology,
Pathology, Armed Washington, DC
4Department of Radiology, Washington Center, Washington, DC 20010. 0361-803X/91/1
Medi-
576-1243
Hospital
appearance
of myositis
December
199i
is a benign, solitary, self-limiting, ossifying soft-tissue mass skeletal muscle. A history of trauma is often inapparent, and we make no distinction between lesions of atraumatic and traumatic origins. The pathogenesis of myositis ossificans is unknown, although the term myositis is a misnomer in that no primary inflammation of skeletal muscle is associated with the process [1]. Synonyms include pseudomalignant osseous tumor of soft tissue, typically
The opinions or 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 varying
relates
Knowledge
Received May 13, 1991 ; accepted after revision July23, 1991.
findings.
to the histologic changes that occur as the dIsorder progresses. of the MR appearance of myositis ossificans is important in that the lesion of the MR imaging characteristics frequently associated with malignancy.
ossificans
ossificans
occurring
extraosseous
within
localized
nonneoplastic
bone
and cartilage
formation,
myositis
ossi-
ficans circumscripta, pseudomalignant myositis ossificans, and heterotopic ossification [1-4]. We describe the MR appearance of eight lesions of histologically proved myositis ossificans
and correlate
Materials
and
these
findings
with other
radiologic
and histologic
studies.
Methods
The radiologic archives of the Armed Forces Institute of Pathology contain 326 cases of histologically proved and radiologically correlated myositis ossificans accumulated in consultation over 40 years. Through a retrospective review, we identified eight patients in whom MR images were available. The clinical histories and radiologic findings in these eight patients form the basis for this report. The study group consisted of five women and three men 1273 years old (mean, 32 years). The thigh was the most common location; it was involved in five cases. One case each occurred in the popliteal fossa, proximal upper arm, and proximal forearm.
Downloaded from www.ajronline.org by Grand Valley State University on 09/22/13 from IP address 148.61.13.133. Copyright ARRS. For personal use only; all rights reserved
1244
KRANSDORF
Fig. 1.-Early myositis ossificans in upper arm of A, Coronal 12-weighted SE MR image (2000/80) (arrow); others are obscured by diffuse surrounding subcutaneous f.t. B, Axial CT scan (bone window) shows incomplete apparent on radiograph (not shown). C, Digital subtraction arterlegram shows a diffuse
29-year-old woman. shows inhomogeneous edema
and adjacent
peripheral
curvilinear
All lesions
(except
one)
were
onal planes and were evaluated definition,
intensity
imaged
in at least
for the following
and homogeneity
two
features:
of the signal,
orthog-
margin
and presence
or
absence of surrounding edema. When edema was present it was graded as diffuse or focal and as mild, moderate, or extensive. In addition
to MR
scans,
intervention; was
images,
all patients
had
and two had arteriograms. the
1 -31
time
days
on duration
patient,
the lesion
histologically Hematoxylin
radiographs,
MR
imaging
six
had
were imaged
and
biopsy
CT
before
or resection
13
days). The clinical age of lesions was of symptoms in seven of eight cases. In one
(mean,
based
In all cases
between
plain
All lesions
was an incidental
the diagnosis
finding.
of myositis
ossificans
was verified [1 5-7].
according to criteria previously described and eosin-stained slides were reviewed without
,
previous
knowledge of each lesion’s duration, and the lesions were classified by the authors as early (recent), intermediate, or late (remote or fully mature) by using the following criteria. Early lesions consisted primanly
of a nonossified
and myofibroblasts, lamellar
bone
central
core
of proliferating
with a minor component
at the periphery;
part of endochondral
hyaline
calcification.
minor or no proliferating entirely of osteoid rimmed
benign
of osteoid
cartilage
Intermediate
could
be present
phenomenon,
lamellar
fibroblastic core; they consisted almost by active osteoblasts and were surrounded
bone.
The
circumscription,
presence
intralesional
or hemosiderin deposition, hematopoiesis, skeletal muscle, intralesional vasculature, sule formation, and edema or myxoid connective
tissue
was
as
lesions had either a
by a shell of mature lamellar bone. Late lesions consisted of mature
fibroblasts
and mature
assessed
exclusively
or absence
of a zoning
inflammation,
hemorrhage
entrapment or atrophy of perilesional fibrosis or capchange in the surrounding
also.
The pathologic features of each lesion were then correlated with the patient’s clinical history, MR images, and other radiologic images. One of these cases has been reported previously [2].
AL.
AJR:157,
mass in upper aspect of arm. Portions subcutaneous fat Edema extends along calcification
tumor blush, indistinguishable
MR examinations were performed with a variety of scanners. Scanning sequences included spin-echo (SE) Ti -weighted, 300-650/ 20-40 (TR/TE), and T2-weighted, 2000-3000/60-90, pulse soquences. In addition, one patient was evaluated with gadopentetate dimeglumine-enhanced MR and another with inversion-recovery MR imaging.
ET
December
of margin are relatively fascial planes separating
well defined muscle and
Edema seen on A is not evident. Mineralization
(arrow).
1991
was not
from that of a malignant neoplasm.
Results MR Findings In early
and
intermediate
lesions,
myositis
ossificans
ap-
peared on T2-weighted SE MR images as a moderately to markedly inhomogeneous soft-tissue mass with increased signal intensity and extensive diffuse surrounding edema. Curvilinear
and irregular
areas
of decreased
signal
intensity
were seen surrounding and coursing through all intermediate lesions and through one of three early lesions, giving these lesions relatively well-defined margins. The margins of two early lesions were difficult to separate from the surrounding edema. Findings on corresponding Ti -weighted images were normal, or showed evidence of a mass by displacement of fascial planes (Figs. 1 and 2). One patient with fluid-fluid levels had increased signal intensity in the muscle surrounding the lesion (Fig. 3). Imaging after administration of gadopentetate dimeglumine (Fig.
in one
2). Changes
patient
compatible
showed with
marked
marrow
enhancement
edema
were
also
detected within the shaft of the femur adjacent to one lesion in the mid thigh. Mature (late) lesions were well-defined inhomogeneous masses with a signal intensity approximating that of fat on both T2- and Ti -weighted images without associated edema. On all pulse sequences, a rim of decreased signal intensity surrounded the lesion and similar areas of decreased signal intensity were apparent within the lesion (Fig. 4).
Other
Radiologic
Findings
were available for review in six patients. The edema detected on MR images was not detected on CT scans. In one early case, however, mild edema was seen CT
scans
marked
in the subcutaneous
adipose
tissue
adjacent
to the
lesion.
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AJR:157,
December
MR
1991
IN
MYOSITIS
OSSIFICANS
1245
D
Fig. 2.-Early myositis ossificans in thigh of 24-year-old woman with pain for 3-4 weeks. A, Axial T2-weighted SE MR image (2800/80) shows inhomogeneous, relatively well-defined mass surrounded by diffuse edema in posterior aspect of thigh. Edema extends along fascial plane separating muscle from subcutaneous fat. B, corresponding axial TI-weightedSE MR image (400/20) shows mass is isointense with skeletal muscle. Area with signal Intensity similar to that of skeletal muscle extends Into subcutaneous fat laterally (arrow), matching area of Increased signal intensity (edema) on A. C, Axial TI-weighted SE MR image (400/20) obtaIned after IV gadopentetate dimeglumine at same level as A and B shows moderate Inhomogeneous enhancement. Edema is seen enhancing along fascial planes (arrow). 0, Lateral radiograph shows densely mineralized mass in posterior aspect of thigh. MineralIzed areas are prsent in A as curvilinear regions of decreased signal. E, Low-power photomicrograph in another patient with similar early lesion shows characteristic zoning phenomenon with central cellular region (asterisk) and peripheral new bone formation. Scattered areas of cartilage formation (arrows) are also seen. Note compressed atrophic skeletal muscle adjacent to right of lesion.
(H and E, original
magnification
x7.5)
Four cases had typical peripheral mineralization (Fig. 3), although it was irregularly shaped and somewhat convoluted in one case. In three ofthese cases, a narrow rim of decreased signal intensity could be seen retrospectively on MR scans. In an early lesion, the peripheral mineralization was incomplete and faint (Fig. i). One mature lesion that had been clinically
apparent
for several years had diffuse mineralization
Arteriography
showed
was available
a distinct
tumor
lesion was hypovascular. Radiographs were available
lesion, no mineralization
in two
blush
cases.
One early lesion
(Fig. 1). A second
in all eight
cases.
was seen, and in another
alization was vague. The remaining mineralized, more so peripherally,
(Fig. 4). mature
In one early
the miner-
early lesion was densely but the mineralization did
not demonstrate
a definite
bonelike
character.
A similar
ap-
pearance was seen in one intermediate lesion. Two intermediate lesions were densely mineralized, with a distinct bonelike character, and were more mature peripherally. One mature lesion was densely mineralized diffusely, and the other had the appearance
of heterotopic
ossification.
Periosteal
reaction
was detected adjacent to one intermediate lesion. In this case and one other, the mass was adjacent to but separate from bone. Histologic
Findings
Histologically,
three
three as intermediate,
cases
were
classified
as early lesions,
and two as late. The central proliferat-
KRANSDORF
1246
ET AL.
AJR:157, December1991
Fig.
3.-Myositis ossificans of intermediate of 31-year-old woman. A, Axial TI-weighted SE MR image (500/40) shows lesion with fluid-fluid levels adjacent to
age in forearm
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...
proximal radius. Areas of increased signal Intensity adjacent to lesion may be related to hemorrhage. B, CT scan (bone window) at level sImilar to that of A shows lesion’s dense peripheral mlnerallzatlon, less apparent on MR. Tissue attenuation within lesion is somewhat lower than that of surrounding soft tissue. C, Radiograph shows densely mineralized mass overlying proximal radius. Peripheral mmeralization Is seen better on CT (B). Retrospectlve review of radiograph obtaIned 45 days ear-
!
:
11crshowed no mineralization. D, Photomicrograph shows mature lamellar bone surrounding hemorrhagic cysts (asterisks). Regions between trabeculae consist of densely
packed fibroblasts and myofibroblasts with ocmultinucleated giant cells. (H and E, magnification x30)
casional original
ing fibroblastic and myofibroblastic core of tissue in intermediate lesions was extremely cellular and had nent myxoid stroma in some cases, resulting in resemblance to nodular fasciitis, both histologically ologically.
The
nodular
fasciitis-like
areas
merged
early and a promia strong and radiwith
de-
posits of osteoid that were rimmed by osteoblasts; these areas in turn were surrounded by a rim of mature lamellar bone at the periphery of the lesions. Five cases had a distinct zoning pattern in which lesional maturation progressed from central, nonossified cellular foci
to osteold to these was a ules. Another pattern and chondroosseous
peripheral rims of mature lamellar bone. One of multinodular lesion with zoning in multiple nodcase (a biopsy) did not show a typical zoning consisted of nodular fasciitis-like areas with nodules;
the other
two were
late lesions
muscle fibers were seen within lesions. As lesions matured, the nodular fasciitis-like areas in the intertrabecular spaces became areas of delicate fibrosis containing thin-walled ectatic
vascular
channels
that
eventually
became
replaced
by
both adipose tissue and dense fibrosis in the most mature lesions. In general, histologic stage correlated well with duration of symptoms, which usually were pain and/or soft-tissue mass. Early lesions were associated with 3-6 weeks of symptoms, intermediate
lesions
with
symptoms
and late lesions with symptoms
of 6-8
weeks’
duration,
of up to 10 years’ duration.
Discussion
and
were composed entirely of calcified, mature lamellar bone. Five cases had hyaline cartilage. One was a late lesion with a cartilaginous cap at the periphery; in the other four cases, the hyaline cartilage was associated with osteoid and undergoing endochondral calcification. All lesions were well circumscribed and rimmed by compressed fibrous connective tissue; most of these were surrounded by atrophic skeletal muscle, and, not infrequently, entrapped, atrophic skeletal
On MR imaging, myositis ossificans was most often a relatively well-defined, inhomogeneous soft-tissue mass. Diffuse surrounding edema was quite prominent in lesions imaged within 8 weeks of the onset of symptoms (Figs. 1 and pattern of diffuse edema has been described previously, as has edema in the adjacent bone marrow [2]. The time required for resolution of the surrounding edema could 2). This
not be determined;
however,
we speculate
that the edema
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AJR:157,
MR IN MYOSITIS
December1991
OSSIFICANS
i 247
Fig. 4.-Mature myositis ossificans in popliteal fossa of 35-year-old man. Mass had been present for several years. A, Axial T2-weighted SE MR image (2500/80) shows a well-defined inhomogeneous mass in popliteal fossa. Areas of increased signal within mass have about the same signal as subcutaneous fat. Similar findings were seen on TI-weighted image (not shown). B, Axial CT scan (bone window) at level similar to that of A shows irregular diffuse mineralization throughout mass. Attenuation coefficient of nonmineralized
area is diffIcult to assess, but may be similar to that of fat.
C, Photomicrograph
adipose
shows
mature
lamellar
bone
corresponding
to densely
mineralized
tissue and delicate fibrous connective tissue. (H and E, original magnification
could persist for several association with mature MR images showed
months. Edema lesions. curvilinear and
was not detected
in
portions
of mass.
Regions
between
trabeculae
consist
of
x30)
The CT appearance of myositis ossificans has been well [1 0-i 3]. CT usually will show a rim of mineralization around lesions after 4-6 weeks. Even when densely mineralized on CT, this rim is much less apparent on MR. The described
irregular
regions
of
decreased signal intensity peripherally as well as within lesions, corresponding to mineralization seen on CT scans and
center
of the mass
may have decreased
CT tissue
attenuation
MR and was often best appreciated retrospectively (Figs. 2 and 3). It was not seen on MR in two early cases in which radiographs were normal or showed only faint mineralization.
[1 0, 13], again reflecting its similarity to nodular fasciitis [8], and corresponding to areas of increased signal intensity on T2-weighted SE MR imaging. Mature lesions may show diffuse ossification (Fig. 4), with corresponding regions of de-
This mineralization
creased
radiographs.
As expected,
this was
delineated
much
less apparent
the lesion from
on
the surrounding
edema or tissue in all but two early cases. The areas of increased signal intensity seen centrally within the early lesions on T2-weighted images are probably related to the extremely cellular central areas of proliferating fibro-
blasts and myofibroblasts within a myxoid stroma or extracellular matrix. These areas are histologically and radiologically similar in appearance to nodular fasciitis [8]. Areas of hyaline cartilage also may contribute to this appearance. The fluid-fluid levels detected in one case (Fig. 3) are consistent
with previous
hemorrhage
[9], which
is not an uncommon
finding in the inner, most immature portion of the lesion. Fluidfluid levels are a nonspecific finding and have been reported in other soft-tissue lesions including synovial sarcoma and
hemangioma [9]. The areas of intermediate signal seen within late myositis ossificans on T2-weighted images reflect areas of fatty infiltration
same
between
areas
bone
trabeculae
have a high signal
within
intensity
the
lesion.
These
on Ti -weighted
on all MR pulse
at least in part, for the contrast
out associated
edema,
ment. Plain radiographs
sequences.
enhancement
identified
within
and we would
in myositis
ossificans
expect
no enhance-
show faint calcifi-
cation within 2-6 weeks after onset of symptoms [1 ]. A sharply circumscribed mass is usually apparent by 6-8 weeks
(although
it may be seen much earlier), becoming
smaller and
mature by 5-6 months [i3, i7, 18]. Although a discussion of the ability to reliably discriminate between benign and malignant lesions on the basis of MR
imaging spectrum
creased
quently
on both pulse sequences.
intensity
the lesion on MR [1 5]. Surrounding enhancement reflects associated edema [1 6]. Mature myositis will be avascular, reflecting the angiographic findings of normal bone [i 4], with-
images. The areas of decreased signal intensity on both pulse sequences represent the bone trabeculae of the lesion itself (Fig. 4). Areas of hemosiderin deposition from previous hemorrhage and fibrosis also may contribute to areas of de-
signal intensity
signal
In the active phase of myositis ossificans, arteriography shows a diffuse tumor blush and fine neovascularity [14]. Although understanding of gadopentetate-dimeglumine enhancement is incomplete, this vascularity is likely responsible,
alone is clearly beyond of MR appearances
the scope of this article, in myositis
ossificans
serves
the to
underscore the nonspecificity of MR imaging in many circumstances. Myositis ossificans, particularly in its early and intermediate phases, displays MR imaging characteristics freequated
with
malignancy.
KRANSDORF
1248
REFERENCES
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40-A:279-298 2. Hanna SL, Magill
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187-1 92 13. Hudson TM. Radiologic-pathologic correlation of musculoskeletal lesions. Baltimore: Williams & Wilkins, 1987:589-604 14. Yaghmal I. Myositis ossificans: diagnostic value of artenography. AJR I977;128:81 1-816
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