AJR 2003; 181:1145-1147
© American Roentgen Ray Society
Contrast-Enhanced MRI of an Early Preosseous Lesion of Fibrodysplasia Ossificans Progressiva in a 21-Month-Old Boy
Hiroaki Hagiwara1,
Noriko Aida1,
Jiro Machida2,
Kazutoshi Fujita1,
Shigeharu Okuzumi2 and
Gen Nishimura3
1 Department of Radiology, Kanagawa Children's Medical Center, 2-138-4
Mutsukawa, Minami-ku, Yokohama 232-8555, Japan.
2 Department of Orthopedics, Kanagawa Children's Medical Center, Yokohama
232-8555, Japan.
3 Japanese Skeletal Dysplasia Consortium, 4-31-2 Yoyogi, Shibuya, Tokyo
151-0053, Japan.
Received January 6, 2003;
accepted after revision February 25, 2003.
Address correspondence to H. Hagiwara
(taichan{at}kc4.so-net.ne.jp).
Introduction
Fibrodysplasia ossificans progressiva, formerly known as myositis
ossificans progressiva, is a rare disorder characterized by congenital
skeletal anomalies and progressive ectopic bone formation in connective
tissue. The initial clinical manifestation is soft-tissue swelling, often in
the neck or back, which spontaneously resolves and leads to the formation of
ectopic bone.
The MRI appearance without contrast enhancement of this early preosseous
lesion has been previously described
[1]. We report the
contrast-enhanced MRI appearance in a 21-month-old boy before the development
of ectopic ossification.
Case Report
A 21-month-old boy had a 3-week history of a rapidly enlarging mass located
in the back. At the time of presentation, physical examination revealed a
diffuse elastic soft mass in his back. There was no erythema on the skin or
local warmth. Biochemical analysis was unremarkable, and he had no family or
past history.
CT performed with moderate contrast enhancement revealed a subcutaneous
hypodense mass in his back (Figs.
1A and
1B) with no calcification in
the mass or infiltration into the muscles. MRI was performed using a Visart
1.5-T system (Toshiba Medical Systems, Tokyo, Japan). T2-weighted images
showed this mass as located in the subcutaneous region and as having high
signal intensity. T1-weighted images showed low signal intensity that was the
same as that of muscle and homogeneous marked enhancement on contrast-enhanced
images.
Three weeks later, follow-up MRI revealed that the lesion had extended to
the bilateral scapular regions (Figs.
1C,
1D,
1E,
1F). The lesion spread in the
subcutaneous region and between muscular bundles predominantly on the left
side, and signal intensity was the same as that in the previous study. Signal
intensity of muscular bundles surrounded by the lesion seemed to be minimal;
however, contrast enhancement was revealed in marginal areas of the muscles.
The child was suspected of having a soft-tissue tumor; however, the diagnosis
of fibrodysplasia ossificans progressiva had not been considered. A diagnostic
biopsy of the subcutaneous mass was performed, and pathologic diagnosis was
infantile desmoid-type fibromatosis.
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Fig. 1C. —21-month-old boy with fibrodysplasia ossificans progressiva.
Axial T2-weighted MRI (TR/TE, 3000/91) shows high-signal-intensity lesion
spread in subcutaneous region and between muscular bundles in bilateral
scapular regions.
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Fig. 1E. —21-month-old boy with fibrodysplasia ossificans progressiva.
Axial fat-suppressed gadolinium-enhanced T1-weighted MRI (565/12) shows lesion
to be markedly enhanced, and peripheral areas of muscular bundles also have
abnormal enhancement.
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Fig. 1F. —21-month-old boy with fibrodysplasia ossificans progressiva.
Coronal fat-suppressed gadolinium-enhanced T1-weighted MRI (565/12) shows
distribution of this lesion from lumbar to neck, predominantly in scapular
region.
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Several weeks after the biopsy, the lesion spontaneously disappeared at
physical examination; however, mild decrease in the active range of motion of
the neck and the left shoulder persisted. On MRI, 5 weeks after the biopsy,
the subcutaneous mass lesion was markedly decreased.
The boy had been followed up without medication for 6 months when normal
length but malformation of the great toes was noticed. Radiographs revealed
deformities in the phalanges of both great toes
(Fig. 1G). Subsequently,
radiography for a skeletal survey was performed, and ectopic ossifications
were noted in the right axillary region
(Fig. 1H). The diagnosis of
fibrodysplasia ossificans progressiva was established by both these
characteristic radiographic findings. Retrospectively, pathologic findings
such as fibromatosis and the MRI appearance were consistent with
fibroproliferative tissue in the early stage of fibrodysplasia ossificans
progressiva.
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Fig. 1H. —21-month-old boy with fibrodysplasia ossificans progressiva.
Radiograph of right humerus, obtained at 6 months after initial presentation
(A), shows ectopic ossifications in right axillary region.
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Discussion
Fibrodysplasia ossificans progressiva is a rare progressive disorder
characterized by ectopic bone formation in connective tissue and skeletal
malformation. It occurs sporadically but may be transmitted as an autosomal
dominant trait with variable expression and complete penetrance. The gene has
recently been mapped to human chromosome 17q21–22, and another study has
localized it to 4q27–31. The pathogenesis of ectopic bone formation is
unknown, but overproduction on bone morphogenetic protein-4 in lesion cells
and lymphocytic cells is reported as one of the factors
[2]. Malformation of the great
toes is most often seen in affected patients, and short thumb, short broad
femoral neck, vertebral abnormalities, and other skeletal anomalies are also
seen.
Initially, fibrodysplasia ossificans progressiva presents as a rapidly
growing mass usually in the neck or paraspinal region in early childhood.
These soft-tissue swellings occasionally resolve but often progress to form
ectopic ossification. The radiologic evidence of this ossification is not
usually detected until 4–6 months after the appearance of a mass
[3]. The average age at the
onset of ectopic ossification has been reported as 5 years. The formation of a
bony bridge causes skeletal contractures, and cardiopulmonary function and
ambulation are severely limited.
The diagnosis is made by two characteristic radiologic findings: ectopic
ossification and skeletal malformation. Connor and Evans
[3] reported that the average
delay in reaching the correct diagnosis after the onset of ectopic
ossification was 3.1 years. Thus, the diagnosis is more difficult when ectopic
ossification is not present, and the duration from the appearance of the
preosseous lesion to diagnosis is expected to be prolonged. However, MRI
findings of a preosseous lesion are sufficient for accurate diagnosis of
fibrodysplasia ossificans progressiva in an early stage despite the absence of
ectopic ossification. A diagnostic biopsy should be avoided because it often
exacerbates ectopic ossification.
The preosseous soft-tissue lesions in the early stage involve fascia,
ligaments, tendons, and skeletal muscle. Pathologic findings vary. The
earliest detected findings obtained from a biopsy specimen of a swollen vastus
lateralis muscle were intense perivascular lymphocytic infiltration into
normal-appearing muscle [4].
However, the soft-tissue mass under the subcutaneous tissue but above the
muscle showed edema with fibroblasts proliferating in a loose stroma against a
loose mucoid background [5].
Furthermore, subsequent matured lesions consist of highly vascular
fibroproliferative tissue indistinguishable from juvenile fibromatosis
[6].
CT provides a more accurate anatomic location of a preosseous lesion, which
appears as swelling and edema of the muscular fascial planes and swelling of
muscular bundles [7]. This
edematous appearance was apparent in our patient; however, homogenous contrast
enhancement was revealed, which was not described in the report by Reinig et
al. [7].
The value of MRI in characterizing the soft-tissue lesion has already been
established. However, the MRI features of this rare disease have not been
previously described, except in the report by Caron et al.
[1]. In their case report, the
soft-tissue lesion in the early stage showed low signal intensity on
T1-weighted images and high signal intensity on T2-weighted images, as seen in
our patient. Caron et al. suggested that the edema might have caused
hyperintensity on T2-weighted images. Contrast enhancement of a preosseous
lesion has not been described, and to our knowledge, ours is the first report
of contrast-enhanced MRI of this lesion. The cause of the marked contrast
enhancement can be explained by high vascularity in fibroproliferative tissue,
which was described by Gannon et al.
[6].
The anatomic location of the preosseous lesion is the most characteristic
finding to ensure the diagnosis of fibrodysplasia ossificans progressiva. The
lesion spreads predominantly along the fascial planes as an interstratified
sheetlike mass between muscular bundles and has no strong tendency to
infiltrate to surrounding muscles. Skeletal muscles were also reported to be
involved and swollen, with increased T2 signal intensity
[1] and, in our patient, as
showing marginal contrast enhancement of muscular bundles. However, the
disease affects primarily connective tissue between muscular bundles, with the
changes in muscle being secondary.
Differential diagnosis is infantile desmoid-type fibromatosis, which
affects children of similar ages and arises as a solitary mass in the skeletal
muscle. The pathologic appearance is indistinguishable from that of the
preosseous lesion of fibrodysplasia ossificans progressiva. However, MRI is
useful to differentiate them because infantile desmoid-type fibromatosis shows
poor margination and heterogeneous signal.
In summary, the preosseous soft-tissue lesion in the early stage of
fibrodysplasia ossificans progressiva showed contrast enhancement on CT and
MRI, mimicking a soft-tissue tumor. However, we believe that the MRI
appearance of spread along the fascial planes is a unique feature, and
diagnosis of fibrodysplasia ossificans progressiva should be considered even
when ectopic ossification does not exist. Radiologists must be aware of
associated malformation of the great toes to confirm the diagnosis, thereby
obviating unnecessary lesion biopsies.
References
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Martel W. MR imaging of early fibrodysplasia ossificans progressiva.
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Engl J Med 1996;335:555
–561[Abstract/Free Full Text]
- Connor JM, Evans DA. Fibrodysplasia ossificans progressiva: the
clinical features and natural history of 34 patients. J Bone Joint
Surg Br 1982; 64:76
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- Gannon FH, Valentine BA, Shore EM, Zasloff MA, Kaplan FS. Acute
lymphocytic infiltration in an extremely early lesion of fibrodysplasia
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- Heidelberger KP, DiPietro M. Fibrodysplasia ossificans progressiva.
Pediatr Pathol1987; 7:105
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- Gannon FH, Kaplan FS, Olmsted E, Finkel GC, Zasloff MA, Shore E.
Bone morphogenetic protein 2/4 in early fibromatous lesions of fibrodysplasia
ossificans progressiva. Hum Pathol 1997;28
: 339–343[Medline]
- Reinig JW, Hill SC, Fang M, Marini J, Zasloff MA. Fibrodysplasia
ossificans progressiva: CT appearance. Radiology1986; 159:153
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Introduction
Case Report
