DOI:10.2214/AJR.05.0588
AJR 2006; 187:807-810
© American Roentgen Ray Society
Tubular Acetabular Intraosseous Contrast Tracking in MR Arthrography of the Hip: Prevalence, Clinical Significance, and Mechanisms of Development
Li-Chang Lien1,
John C. Hunter2 and
Yi-Sheng Chan3
1 Department of Medical Imaging and Intervention, Chang Gung Memorial Hospital,
College of Medicine, Chang Gung University, 5 Fu-Hsing St., Gui-Shan, Tao-Yuan
33300, Taiwan.
2 Department of Radiology, Musculoskeletal Section, University of California
Davis School of Medicine, Sacramento, CA.
3 Department of Orthopedics, Chang Gung Memorial Hospital, College of Medicine,
Chang Gung University, Taiwan.
Received April 4, 2005;
accepted after revision May 9, 2005.
Address correspondence to L. C. Lien
(lclienmdrad{at}yahoo.com).
Abstract
OBJECTIVE. The purpose of this study was to describe tubular
intraosseous tracking of contrast medium in the acetabular fossa, to our
knowledge a previously undocumented imaging finding in MR arthrography of the
hip, and to discuss its prevalence, clinical significance, and possible
mechanisms of development.
CONCLUSION. Tubular acetabular intraosseous contrast tracking is a
common MR arthrographic finding that seems to have little clinical
significance. Although the exact pathophysiologic mechanism is unknown, we
presume repeated pumping of joint fluid through the nutrient foramina of the
acetabular fossa may be one mechanism.
Keywords: hip • MR arthrography
Introduction
MR arthrography has been the study of choice for evaluating pathologic
changes in the hip joint
[1-4].
In a few of our patients undergoing MR arthrography of the hip because
acetabular labral tears were suspected, the images showed no acetabular labral
tears but did show tubular intraosseous tracking of contrast medium near the
posterior-anterior margin of the acetabular fossa. To our knowledge this
finding is undocumented in the literature on MR arthrography. The purpose of
this study was to describe this imaging finding and to discuss its prevalence,
clinical significance, and possible mechanisms of development.
Subjects and Methods
Patients
We retrospectively reviewed MR arthrographic images of the hips of 119
patients (75 females, 44 males; age range, 14-73 years; mean age, 39 years)
consecutively examined at two institutions from July 2001 to May 2004 because
of the clinical impression of acetabular labral tear. Twenty-six of the
patients underwent bilateral hip imaging. Four of these patients had symptoms
in both hips. The 22 patients with unilateral hip pain underwent simultaneous
imaging of both hips as a control study, which had institutional review board
approval. Each patient gave informed consent before the procedure and after a
thorough explanation of the procedure.
Imaging Techniques
All patients underwent fluoroscopy-guided injection of 1:200 diluted
gadodiamide contrast medium (Omniscan 0.5 mmol/mL, Amersham Health Ireland)
into the hip joint by the anterior approach. The volume of injected contrast
medium ranged from 10 to 20 mL depending on patient tolerance. MR arthrography
was performed with a 1.5-T Signa (GE Healthcare) or Vision (Siemens Medical
Solutions) system. With the Signa system, a torso coil was used with an axial
3D spoiled gradient-recalled acquisition in the steady state pulse sequence
(TR/TE, 33.3/4; flip angle, 30°; matrix, 512 x 256; field of view,
30 x 30 cm; effective slice thickness, 2.2 mm; number of acquisitions,
1) and an axial-coronal-sagittal fat-suppressed T1-weighted spin-echo pulse
sequence (500/11; matrix, 320 x 224; field of view, 30 x 30 cm;
slice thickness, 3.5 mm; number of acquisitions, 2). With the Vision system, a
surface coil was used with a fat-suppressed axial 3D fast low-angle shot pulse
sequence (48/11; flip angle, 40°; matrix, 256 x 256; field of view,
15 x 15 cm; effective slice thickness, 1.5 mm; number of acquisitions,
1). Coronal and sagittal reformation along the plane of the acetabular rim was
performed. In one patient, simultaneous MR and CT arthrography was performed
with a mixture of 75% iothalamate meglumine (Conray 60, Mallinckrodt Canada)
and 1:200 diluted gadodiamide as the intraarticular contrast medium. CT was
performed with an MDCT system (Somatom Sensation 16, Siemens Medical
Solutions).
Imaging Analysis
Two musculoskeletal radiologists, one with 6 and the other with more than
10 years of experience, reviewed the images by consensus. If tubular
intraosseous contrast tracking was present around the acetabular fossa, we
recorded the location of the track origin, the dimensions of the track
orifice, track length (measured with the 3D spoiled gradient-recalled
acquisition in the steady state pulse sequence on the Signa system and with
the 3D fast low-angle shot pulse sequence on the Vision system), whether
dilatation was present at the blunt end of the track (clubbing phenomenon),
and whether a subchondral cyst was present in the weight-bearing acetabular
roof.
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Fig. 1A —54-year-old woman who underwent bilateral hip imaging for
suspected unilateral acetabular labral tears. Consecutive axial fat-suppressed
3D fast low-angle shot (TR/TE, 48/11; flip angle, 40°) MR arthrographic
images show asymptomatic hip in craniocaudal sequence. Normal posterior margin
(arrowhead) of acetabular fossa.
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Fig. 1B —54-year-old woman who underwent bilateral hip imaging for
suspected unilateral acetabular labral tears. Consecutive axial fat-suppressed
3D fast low-angle shot (TR/TE, 48/11; flip angle, 40°) MR arthrographic
images show asymptomatic hip in craniocaudal sequence. Tubular intraosseous
contrast tracking (arrow) arising from junction of articular
cartilage and posterior margin of acetabular fossa.
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Fig. 1C —54-year-old woman who underwent bilateral hip imaging for
suspected unilateral acetabular labral tears. Consecutive axial fat-suppressed
3D fast low-angle shot (TR/TE, 48/11; flip angle, 40°) MR arthrographic
images show asymptomatic hip in craniocaudal sequence. Blind end of
intraosseous contrast tracking shows mild dilatation known as clubbing
phenomenon (asterisk).
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Statistical Analysis
We used a t test (SPSS) to compute the statistical significance of
the difference between the ages of the subjects with tracks and that of the
subjects without tracks.
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Fig. 2A —43-year-old woman with suspected acetabular labral tears.
Axial fat-suppressed 3D fast low-angle shot (TR/TE, 48/11; flip angle,
40°) MR arthrographic image of hip shows posterior acetabular intraosseous
contrast tracking (arrow) at level of mid acetabular fossa.
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Fig. 2B —43-year-old woman with suspected acetabular labral tears.
Arthrographic CT scan of hip shows posterior acetabular intraosseous contrast
tracking (arrow) at level of mid acetabular fossa. Small gap exists
between track orifice (white arrowhead) and junction (black
arrowhead) of articular cartilage and acetabular fossa.
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Results
Tubular acetabular intraosseous contrast tracking was seen in 23 (16%) of
145 examined hips and in 19 (15%) of 123 symptomatic hips. The origins of the
tracks were consistently located at the posterior-anterior margin of the
acetabular fossa. Ten tubular tracks originated immediately from the junction
of the articular cartilage and the acetabular fossa
(Fig. 1B). The other tracks
originated from the margin of the acetabular fossa close to the junction of
the articular cartilage and the acetabular fossa (Figs.
2B and
3A). All 23 hips had posterior
tracks (Figs. 1A,
1B,
1C,
2A,
2B,
3A,
3B,
3C, and
3D); two had concomitant
anterior tracks, which were shorter and smaller in dimension than the
posterior tracks (Fig. 3A). The
track orifice measured 0.6-1.5 mm (mean, 1.2 mm); the track length was 0.4-1.7
cm (mean, 1.1 cm). Sixteen (70%) of 23 tracks were dilated at the blunt end
(clubbing phenomenon) (Figs. 1C
and 3D). Subchondral cysts in
the weight-bearing acetabular roof were identified in no hips with tubular
intraosseous tracking and in three hips without tracking (Figs.
4A and
4B). The patients with tubular
intraosseous tracking were 41 ± 14.6 years old (mean ± SD), and
those without tracking were 39.9 ± 14.2 years old (p = 0.735).
Tubular tracks were identified in 4 (18%) of the symptomatic and 4 (18%) of
the asymptomatic hips in 22 patients who underwent control studies of
asymptomatic hips.
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Fig. 3A —52 year-old woman who underwent bilateral hip imaging for
suspected unilateral acetabular labral tears. Consecutive axial fat-suppressed
3D fast low-angle shot (TR/TE, 48/11; flip angle, 40°) MR arthrographic
images in cranial-caudal sequence show asymptomatic hip. Anterior tubular
track (A) originates from margin (arrow) of acetabular fossa close to
articular cartilage (arrowhead).
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Fig. 3B —52 year-old woman who underwent bilateral hip imaging for
suspected unilateral acetabular labral tears. Consecutive axial fat-suppressed
3D fast low-angle shot (TR/TE, 48/11; flip angle, 40°) MR arthrographic
images in cranial-caudal sequence show asymptomatic hip. Anterior tubular
track (A) originates from margin of acetabular fossa. Posterior tubular track
(P) originates from junction (arrow) of posterior margin of
acetabular fossa and articular cartilage.
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Fig. 3C —52 year-old woman who underwent bilateral hip imaging for
suspected unilateral acetabular labral tears. Consecutive axial fat-suppressed
3D fast low-angle shot (TR/TE, 48/11; flip angle, 40°) MR arthrographic
images in cranial-caudal sequence show asymptomatic hip. Posterior tubular
track (P) originates from junction of posterior margin of acetabular fossa and
articular cartilage.
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Fig. 3D —52 year-old woman who underwent bilateral hip imaging for
suspected unilateral acetabular labral tears. Consecutive axial fat-suppressed
3D fast low-angle shot (TR/TE, 48/11; flip angle, 40°) MR arthrographic
images in cranial-caudal sequence show asymptomatic hip. Dilatation of blind
end of posterior tubular track known as clubbing phenomenon
(asterisk) is evident.
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Fig. 4A —50-year-old man with suspected acetabular labral tears.
Coronal (A) and sagittal (B) fat-suppressed T1-weighted MR
arthrographic images (TR/TE, 500/11) show ovoid subchondral cyst
(arrows) in weight-bearing region of bony acetabulum. Intermediate
signal intensity of cyst content without contrast fill-in is evident. No
definite acetabular labral tears are present.
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Fig. 4B —50-year-old man with suspected acetabular labral tears.
Coronal (A) and sagittal (B) fat-suppressed T1-weighted MR
arthrographic images (TR/TE, 500/11) show ovoid subchondral cyst
(arrows) in weight-bearing region of bony acetabulum. Intermediate
signal intensity of cyst content without contrast fill-in is evident. No
definite acetabular labral tears are present.
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Discussion
MR arthrography is the imaging study of choice in the diagnosis of
acetabular labral tears. Recent reports have shown its pitfalls and variations
[4,
5]. Our results show that
tubular acetabular intraosseous tracking of contrast medium, to our knowledge
a previously unreported imaging finding, occurred in 15% of patients
undergoing hip MR arthrography for suspected acetabular labral tears. Given
the high prevalence of such an imaging finding in our series, the relation of
the existence of tears to hip pain may be an issue. It was interesting that
among 22 patients undergoing control studies, the number of cases (n
= 4) of tubular contrast tracking was the same in symptomatic and asymptomatic
hips. Interpretation based on this small number of subjects is difficult.
Further study with a larger control group should resolve this issue.
Nevertheless, because the number of cases was the same in the two groups, we
speculate that the finding of tubular intraosseous contrast tracking in
evaluations for acetabular labral tears may have little clinical
significance.
Because the contrast tracking consistently originated from the
posterior-anterior margin of the acetabular fossa, it is reasonable to
attribute the mechanism of development to anatomic and developmental factors.
Other possibilities are degeneration-associated cysts and intraosseous
ganglia.
The articulating surface of the acetabulum is well protected by hyaline
cartilage. The superior portion of the acetabular fossa is void of synovial
lining [6]. Nutrient foramina
are located in the margins of the acetabular fossae, where acetabular branches
of obturator vessels ramify into the bony acetabulum
[7]. Repeated pumping of joint
fluid through these anatomically vulnerable regions may produce channels with
dilatation at the blind ends (clubbing phenomenon)
(Fig. 5).
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Fig. 5 —Drawing shows typical locations of tubular acetabular
intraosseous contrast tracking over posterior-anterior margin
(arrowheads) of acetabular fossa, subchondral cyst over
weight-bearing surface of acetabular roof (star) and ischiopubic
flange of triradiate cartilage over center of acetabular fossa, and junction
(arrows) of pubis and ischium. IL = ilium. PU = pubis, IS =
ischium.
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Incomplete bone fusion at the vertical ischiopubic flange of triradiate
cartilage, in theory, may form a vertical cleft in the middle of the
acetabular fossa [8].
Nevertheless, the contrast tracking we observed was tubular rather than cleft
in shape. The track entry locations in our series were in the margins rather
than the centers of the acetabular fossae
(Fig. 5).
Degeneration-associated cysts of the acetabulum typically occur on the
weight-bearing surface of the acetabular roof (Figs.
4A,
4B, and
5), are subchondral in
location, and show evidence of nearby hyaline cartilage wear. These cysts
rarely communicate freely with the joint space. When they do, bone debris and
fibrous material may partially fill the cystic space. In addition,
degenerative cysts tend to occur in older patients
[9,
10].
Intraosseous ganglia are solitary unilocular or multilocular cystic lesions
in the epiphyses of bones, commonly around the ankle, knee, and wrist
[11]. These ganglia have
intermediate and high signal intensity on T1- and T2-weighted images,
respectively. The exact pathogenesis is debated; however, intraosseous ganglia
usually do not communicate with joint spaces
[9,
11,
12].
There are two possible reasons for the high prevalence (
15%) of
contrast tracking in the current study. First, unlike subjects in the current
study, most previously described subjects in studies of MR arthrography of the
hip have been from western populations
[1-4].
Ethnic differences may exist. Second, also partly related to ethnic factors,
the amount of contrast medium injected in the current study was equal to
[3] or slightly greater than
[1,
2,
4] the amounts reported in the
literature. With the relatively smaller body shape in our population,
intraarticular pressure was theoretically higher, and the potential
intraarticular channels in our subjects were more likely to open and fill.
Because the entry site of the track is tiny and deep in the margin of the
acetabular fossa, which is difficult to evaluate with arthroscopy, surgical
correlation is not available. Further study with imaging-cadaver correlation
may provide additional information about the pathophysiologic mechanism.
In conclusion, tubular acetabular intraosseous contrast tracking during MR
arthrography of the hip is a common finding that seems to have little clinical
significance. Although the exact pathophysiologic mechanism is unknown, we
presume repeated pumping of joint fluid through the nutrient foramina of the
acetabular fossa is a mechanism of development.
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Abstract
Introduction
