AJR 2001; 177:1391-1395
© American Roentgen Ray Society
Intraarticular Osteoid Osteoma
Sonographic Findings in Three Patients with Radiographic, CT, and MR Imaging Correlation
Farhad S. Ebrahim1,2,
Jon A. Jacobson1,
John Lin1,3,
Jeffrey A. Housner4,
Curtis W. Hayes1 and
Donald Resnick5
1
Department of Radiology, University of Michigan Medical Center, 1500 E.
Medical Center Dr., Ann Arbor, MI 48109-0326.
2
Present address: Department of Radiology, McMaster University, 1200 Main St.
W., Hamilton, Ontario L8N 3Z5, Canada.
3
Valley Radiologists, Ltd., 5322 W. Northern Ave., Glendale, AZ 85301.
4
Department of Family Medicine and Orthopedic Surgery, Medsport Domino's Farms,
24 Frank Lloyd Wright Dr., Ann Arbor, MI 48105.
5
Department of Radiology, University of California San Diego Veterans
Administration Medical Center, 3350 La Jolla Village Dr., San Diego, CA
92161.
Received May 16, 2001;
accepted after revision June 28, 2001.
Partially supported by grant SA-360 from the Veterans Administration and by
Acoustic Imaging, Phoenix, AZ.
Address correspondence to J. A. Jacobson.
Abstract
OBJECTIVE. Intraarticular osteoid osteoma often has subtle
radiographic findings and nonspecific clinical features; further diagnostic
workup of unexplained joint pain may involve musculoskeletal sonography. We
describe the sonographic features of intraarticular osteoid osteoma in three
consecutive patients with radiographic, CT, and MR imaging correlation.
CONCLUSION. The sonographic findings of painful cortical
irregularity and focal synovitis should raise the possibility of
intraarticular osteoid osteoma, prompting the search for characteristic
findings on correlative imaging studies.
Introduction
Osteoid osteoma is a benign bone lesion of uncertain origin that accounts
for approximately 10% of all benign bone tumors
[1]. When intraarticular, the
classic radiolucent nidus is often overlooked at radiography because reactive
sclerosis may be minimal or absent
[2,3,4].
The subtle radiographic appearance combined with a nonspecific clinical
presentation often leads to delay of diagnosis and further evaluation using
advanced imaging studies
[5].
CT and MR imaging findings of osteoid osteoma are well known. On CT, an
osteoid osteoma is characterized by a low-attenuation nidus with possible
internal calcification and variable surrounding sclerosis
[6]. On MR imaging, the nidus
shows low or intermediate signal on T1-weighted images, variable signal on
T2-weighted images, and variable contrast enhancement after IV gadolinium
administration [6]. In
addition, high signal in the bone marrow and soft-tissue abnormalities on
T2-weighted images may be found adjacent to the osteoid osteoma
[6].
In comparison with CT and MR imaging, less is known about the sonographic
features of osteoid osteoma. Osteoid osteomas in an extraarticular location
have been localized on sonography by identification of cortical irregularity
and a vascular nidus [7]. In a
letter, Malghem et al. [8]
described effusion, proliferative synovitis, or both, associated with
intraarticular osteoid osteomas of the femoral neck and visualization of the
nidus itself.
Because of the nonspecific clinical features and subtle radiographic
appearance of an intraarticular osteoid osteoma, sonography may be used to
investigate unexplained joint symptoms and to evaluate any associated
synovitis. We retrospectively describe the sonographic features of
intraarticular osteoid osteoma in three patients with radiographic, CT, and MR
imaging correlation.
Materials and Methods
Three consecutive patients were identified in the clinical practice of one
of the investigators between July 1995 and November 2000 as having undergone
sonography of a joint involved with an intraarticular osteoid osteoma. In two
patients, the distal humerus was involved at the elbow joint; in one patient,
the distal metatarsal was involved at the metatarsophalangeal joint. The three
patients studied included one man and two women; their age range was 26-42
years (mean age, 30 years). Each patient had pain of at least 1 year's
duration.
Each diagnosis was confirmed at pathology after surgery or by
characteristic features on CT examination. Sonography was performed by a
fellowship-trained musculoskeletal radiologist with experience in
musculoskeletal sonography. Sonography equipment included a 7.5-MHz linear
transducer (Model 5200; Acoustic Imaging, Phoenix, AZ) and a 10- to 12-MHz
linear transducer (HDI 5000; Advanced Technology Laboratories, Bothell, WA).
Liberal transmission gel was used in place of the stand-off pad.
This study was granted exemption by our Institutional Review Board.
Sonographic images were retrospectively reviewed by consensus of two
fellowship-trained musculoskeletal radiologists with experience in
musculoskeletal sonography. One of the reviewers performed all three of the
sonographic examinations; the other reviewer was asked to perform one of the
three sonographic examinations for another opinion. Images were assessed for
joint effusion, cortical abnormality, synovitis, posterior acoustic
enhancement, and increased blood flow during color Doppler and power Doppler
sonography (when available). The criterion for joint effusion was anechoic
distention of the joint capsule. Cortical abnormality was identified as an
irregular contour or disruption of the normally smooth and hyperechoic bone
cortex. Synovitis was identified as hypoechoic or isoechoic distention of the
joint capsule relative to muscle. The location of the synovitis was also
noted. The presence and location of increased blood flow on color Doppler or
power Doppler sonography within a distended joint was also used to indicate
synovitis.
Correlative radiographs, CT, and MR imaging studies were also
retrospectively reviewed by one of the investigators and compared with the
sonographic findings. Radiographs were evaluated for the presence of a
radiolucent nidus, surrounding sclerosis, periostitis, and synovitis. CT
findings such as low-attenuation nidus, internal calcification, and
surrounding sclerosis were also assessed. MR images were evaluated for signal
intensity of the nidus and adjacent bone marrow and for soft-tissue
abnormalities.
Results
In each of the three consecutive patients with intraarticular osteoid
osteoma, retrospective review of the sonographic images showed focal cortical
irregularity and adjacent focal hypoechoic synovitis at the site of the
intraarticular osteoid osteoma (Figs.
1A,1B,1C,1D,1E,1F,2A,2B,2C,2D,3A,3B,3C,3D).
In one patient, the bone cortex was discontinuous over the osteoid osteoma
(Fig. 1A). The apparent osteoid
osteoma nidus was hypoechoic on the sonographic images with posterior acoustic
enhancement and was associated with a penetrating vessel (Fig.
1A,1B,1C).
The adjacent synovitis showed notable hyperemia in the patient who had color
Doppler and power Doppler sonography (Fig.
1C). At the time of the sonographic examination, intense pain was
produced when the transducer was pressed over the area of abnormal cortical
irregularity and adjacent synovitis.
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Fig. 1A. —42-year-old woman with osteoid osteoma of distal humerus.
Sagittal sonogram of posterior humerus shows cortical irregularity (between
solid straight arrows) at site of osteoid osteoma with adjacent focal
hypoechoic synovitis (curved arrow). Also note cortical discontinuity
with posterior acoustic enhancement (arrowheads) at the site of
apparent hypoechoic osteoid osteoma nidus (open arrow).
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Fig. 1B. —42-year-old woman with osteoid osteoma of distal humerus.
Axial sonogram of posterior humerus shows cortical irregularity (between
long straight arrows) at site of osteoid osteoma with adjacent focal
hypoechoic synovitis (curved arrow). Note small effusion in olecranon
fossa (short arrow).
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Fig. 1C. —42-year-old woman with osteoid osteoma of distal humerus.
Corresponding color Doppler axial sonogram of posterior humerus shows
hyperemia (curved arrow) of focal synovitis with apparent vessel
(straight arrow) entering cortex at site of osteoid osteoma.
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Fig. 1D. —42-year-old woman with osteoid osteoma of distal humerus.
Axial T1-weighted spin-echo MR image (TR/TE, 50/18) shows intermediate signal
osteoid osteoma (solid straight arrow) with internal low signal. Note
adjacent synovitis (curved arrow) and bone marrow edema (open
arrow).
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Fig. 1E. —42-year-old woman with osteoid osteoma of distal humerus.
Lateral radiograph of elbow shows radiolucent nidus (straight arrow)
with internal calcification and adjacent sclerosis (curved
arrow).
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Fig. 2A. —26-year-old man with osteoid osteoma of distal humerus.
Sagittal sonogram of posterior humerus shows cortical irregularity
(straight arrow) and adjacent hypoechoic synovitis (curved
arrow) at site of osteoid osteoma.
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Fig. 2C. —26-year-old man with osteoid osteoma of distal humerus.
Anteroposterior elbow radiograph shows lucent osteoid osteoma (arrow)
with minimal surrounding sclerosis and possible intrinsic calcification.
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Fig. 2D. —26-year-old man with osteoid osteoma of distal humerus. Axial
CT image shows low attenuation nidus (straight arrow) of osteoid
osteoma with intrinsic calcification and surrounding sclerosis (curved
arrow).
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Fig. 3A. —22-year-old woman with osteoid osteoma of second metatarsal
bone. Dorsal sonogram of distal second metatarsal bone shows cortical
irregularity (straight arrow) and adjacent focal hypoechoic synovitis
(curved arrow) at site of osteoid osteoma.
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Fig. 3B. —22-year-old woman with osteoid osteoma of second metatarsal
bone. Sagittal T2-weighted inversion recovery MR image (TR/TE 4845/30;
inversion time, 140) shows focal increased signal of dorsal second metatarsal
bone and adjacent soft tissues (arrow).
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Correlative imaging studies included radiography, MR imaging, and CT (Figs.
1A,1B,1C,1D,1E,1F,2A,2B,2C,2D,3A,3B,3C,3D).
Radiography showed the lucent nidus of the osteoid osteoma whereas CT showed a
low-attenuation nidus with internal calcification in all three patients. Both
radiography and CT showed periosteal new bone formation and trabecular
sclerosis in the two cases that involved the distal humerus (Figs.
1A,1B,1C,1D,1E,1F
and
2A,2B,2C,2D).
The nidus of the osteoid osteoma showed intermediate signal intensity on T1-
and T2-weighted MR images in two patients (Figs.
1A,1B,1C,1D,1E,1F
and
2A,2B,2C,2D),
and high signal intensity on T2-weighted images in one patient (Fig.
3A,3B,3C,3D).
Fluid signal intensity bone marrow edema and synovitis were noted in two
patients adjacent to the intraarticular osteoid osteoma (Figs.
1A,1B,1C,1D,1E,1F
and
2A,2B,2C,2D).
In the two patients with involvement of the distal humerus, the diagnosis
of intraarticular osteoid osteoma was not suggested prospectively at
radiography or MR imaging. In the third patient, who had involvement of the
distal metatarsal, the prospective diagnosis of intraarticular osteoid osteoma
was considered. Sonography was used to further evaluate unexplained joint pain
and to assess for synovitis. Although the diagnosis of osteoid osteoma was not
known at the time of the sonographic examination, radiographic and MR imaging
studies were available for review in two patients. CT was performed after
completion of the sonographic examinations.
In the two patients with distal humerus involvement, the pathologic
diagnosis of osteoid osteoma was confirmed after surgical removal of the
lesion. In the patient who had involvement of the distal metatarsal,
pathologic confirmation of the osteoid osteoma was not possible given the
small size of the lesion removed at surgery; however, the clinical findings
and results from the correlative imaging studies (Fig.
3B,3C,3D)
were characteristic of an osteoid osteoma. This patient remains asymptomatic
without analgesics 6 months after surgical resection.
Discussion
We describe the sonographic findings of intraarticular osteoid osteomas in
three patients. In each patient, cortical irregularity at the site of an
osteoid osteoma was associated with focal hypoechoic synovitis and pain with
transducer pressure (Figs. 1A,
1B,
2A,
3A). In one patient, the
cortex was discontinuous over the osteoid osteoma, which allowed visualization
of an apparent hypoechoic nidus (Figs.
1A and
1B); color Doppler sonography
identified a vessel where it entered the osteoid osteoma
(Fig. 1C). Hyperemia of the
focal synovitis was also present in the one patient that had color Doppler
sonography (Fig. 1C). The focal
nature of the synovitis and cortical irregularity prompted additional imaging
studies or review of available imaging studies, which revealed the nidus of an
osteoid osteoma.
Osteoid osteomas have been categorized by location as subperiosteal,
cortical, and cancellous [5].
The classic radiographic appearance of the more common cortical osteoid
osteoma is that of a radiolucent nidus, with or without internal calcification
and surrounding sclerosis or cortical thickening
[1,
5]. This is in contrast to
intraarticular osteoid osteomas, which are are characterized by little or no
reactive sclerosis; for this reason, the radiolucent nidus is often overlooked
on radiographs [5]. Although
endosteal sclerosis may occur with intraarticular osteoid osteomas, periosteal
new bone is absent, because the periosteum is not present within the joint
capsule [3]. Osseous sclerosis
and periostitis associated with intraarticular osteoid osteomas have been
noted in the elbow [5]. These
findings are seen in the two patients in our study who had elbow involvement
(Figs.
1A,1B,1C,1D,1E,1F
and
2A,2B,2C,2D).
Osteoid osteomas tend to occur in patients between the ages of 10 and 30
years [5]. One of the patients
with involvement of the distal humerus in this study was 42 years old at the
time of the diagnosis, although her symptoms were controlled with
antiinflammatory medication for more than 3 years. Moser et al.
[5] described six patients with
intraarticular osteoid osteoma of the elbow, three of whom were more than 36
years old.
The differential diagnosis for intraarticular cortical irregularity on
sonography includes inflammatory arthritis
[9]. Patient history, age, and
monoarticular involvement may allow differentiation of intraarticular osteoid
osteoma from a systemic inflammatory synovitis. Osteochondritis dissecans can
produce subchondral flattening and irregularity of the cortical bone
[10], whereas an
intraarticular fracture may appear as cortical discontinuity or step-off
[11]. Correlation with
radiography and patient history will differentiate these abnormalities from an
intraarticular osteoid osteoma.
The diagnosis of an intraarticular osteoid osteoma is often delayed for
months or years [2]. Patients
present with a painful joint that may be warm and stiff, suggesting synovitis
[2]. Joint effusion or
synovitis, or both, may be evident on radiography, depending on the specific
joint that is involved [2]. The
cause of synovitis associated with intraarticular osteoid osteoma is
uncertain; however, prostaglandin has been implicated because levels of this
potent inflammatory mediator are elevated in osteoid osteomas
[3]. Synovitis associated with
intraarticular osteoid osteomas is often hyperplastic, having prominent
lymphoid aggregates that may simulate inflammation from rheumatoid or
psoriatic arthritis [3]. On
sonography, hypoechoic synovitis may appear similar to complex fluid. The
findings of joint recess compressibility and collapse on joint movement and of
motion of internal echoes on transducer pressure suggest complex fluid;
hyperemia revealed by color Doppler or power Doppler sonography suggests
synovitis [12].
Limitations of this study include potential selection bias because our
three patients were identified through the personal experience of one of the
investigators. However, the three subjects were consecutive patients having
sonographic evidence of a possible intraarticular osteoid osteoma. Also, the
accuracy of sonography in the diagnosis of intraarticular osteoid osteoma
cannot be determined on the basis of our investigation results. It is possible
that other pathologic conditions may have an appearance similar to that which
we have described in intraarticular osteoid osteoma.
In summary, the presence of painful cortical irregularity and adjacent
focal synovitis in patients undergoing sonography should warrant careful
examination of correlative imaging studies for the possible presence of an
intraarticular osteoid osteoma.
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Abstract
Introduction
