Download Acetabular labrum: Pitfalls of MR imaging

Acetabular labrum: Pitfalls of MR imaging
Poster No.:
C-2218
Congress:
ECR 2010
Type:
Educational Exhibit
Topic:
Musculoskeletal
Authors:
M. Castro, A. B. Almeida, N. Silva, R. H. Castro, A. Vieira; Porto/
PT
Keywords:
Acetabular labrum, Tears, MRI pitfalls
DOI:
10.1594/ecr2010/C-2218
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Page 1 of 65
Learning objectives
• To understand and identify the different pitfalls that may reduce the specificity of the
MR diagnosis of acetabular labral tears.
Images for this section:
Fig. 1: Fig. 1) Axial (a), coronal (b) and sagittal (c) T1-weighted MR arthrography images
show the normal labrum (circles) as a low signal triangular structure and the transverse
ligament (arrows) connecting the anterior and posterior labrum.
Page 2 of 65
Fig. 2: Fig. 3) Axial T1-weighted MR arthrography image shows contrast material
extending into the acetabular/labral interface, with a complete detachment of the labrum
from the acetabular rim (arrow), findings suggestive of a labral tear. A synovial pit is also
seen in the anterior junction of the head and neck of the femur (circle). These finding is
frequently associated with situations of femoro-acetabular impingement, one of the major
causes of labral tears.
Page 3 of 65
Fig. 3: Fig. 7) Coronal T1-weighted MR arthrography image demonstrates a flattened
labrum with increased interstitial signal.
Page 4 of 65
Fig. 4: Fig. 10) Coronal T1-weighted MR arthrography image where is easy to see the
linear high signal under the base of the labrum (arrow) presenting with the same signal
intensity of the contrast material. This is not cartilage undercutting the labrum, this is a
labral tear.
Page 5 of 65
Background
• As orthopedic surgeons become more comfortable performing arthroscopic surgery
on the hip joint, labral abnormalities are more frequently being addressed by means
of minimally invasive surgery. Accurate preoperative identification of labral tears by the
radiologist has therefore become an area of increasing interest.
• Different authors reported sensitivity values of MR arthrograms from 66% to 100% and
specificity values from 44% to 100%.
• Although it is obvious that some labral tears may not be visualized on MR arthrograms, it
is less evident why false-positive MR arthrograms occur and what these findings actually
represent.
• The presence of normal anatomic variants is the probable explanation for an
important number of false-positive MR findings in some of the previous published
studies.
Images for this section:
Page 6 of 65
Fig. 1: Fig. 4) Sagittal STIR-weighted image shows complete detachment of the anterior
labrum (blue arrow), and a small paralabral cyst (white arrow). These findings are
diagnostic for a labral tear. This patient also has signs of AVN of the femoral head.
Page 7 of 65
Fig. 2: Fig. 11) Axial T1-weighted image showing the iliopsoas tendon (blue arrow)
crossing the anterior labrum (white arrow). Inbetween these two structures is a line of
high signal that should not be mistaken by a labral tear.
Page 8 of 65
Fig. 3: Fig. 14) Axial T2 GRE-weighted image where is possible to see the normal
labroligamentous sulcus (arrow) at the junction of the anterior labrum with the transverse
ligament.
Page 9 of 65
Fig. 4: Fig. 19) Axial T1-weighted MR arthrography showing a partial separation of the
posterior labrum from the underlying cartilage (arrow), suggestive of a sublabral recess.
Page 10 of 65
Imaging findings OR Procedure details
Functions of the Acetabular Labrum
• Shock absorption
• Joint lubrication
• Pressure distribution
• Aiding in stability of the hip joint
Etiology of the Labral Lesions
• The etiology of labral tears includes:
1.
2.
3.
4.
5.
Trauma
Femoroacetabular impingement
Capsular laxity/hip hypermobility
Dysplasia
Degeneration
Importance of the Labral Lesions
• Previously thought to be a relatively uncommon injury, acetabular labral tears are
becoming diagnosed with increasing frequency because of improvements in MRI and
arthroscopic techniques.
• Prevalence of labral tears in patients with hip or groin pain has been reported to be
22-55%.
• Besides the symptomatic complaints due to labral tears, the importance of the pathology
is its association with degenerative changes:
1.
2.
3.
4.
73% of patients with fraying or tearing of the acetabular labrum have
chondral damage.
The chondral damage is more severe in patients with labral lesions.
In 94% of the patients, the articular damage occurs in the same zone of the
acetabulum as the labral lesions.
The relative risk of significant chondral erosion approximately doubles in the
presence of a labral lesion.
Acetabular Labrum Anatomy
• The acetabulum covers 170 ° of the femoral head. The acetabular labrum is a
fibrocartilaginous structure that outlines the acetabular socket.
• It is a continuous, low signal, usually triangular structure that attaches to the rim of the
acetabulum and is completed at the inferior portion by the transverse acetabular ligament
over the acetabular notch (fig. 1).
Page 11 of 65
Fig.: Fig. 1) Axial (a), coronal (b) and sagittal (c) T1-weighted MR arthrography images
show the normal labrum (circles) as a low signal triangular structure and the transverse
ligament (arrows) connecting the anterior and posterior labrum.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Labral Tears Diagnosis
• Labral tears present with anterior hip or groin pain, and less commonly buttock pain.
Frequently, there are also mechanical symptoms including clicking, locking, and giving
way.
• Most reported tears occur at the anterior portion of the labrum.
• In Japan the majority of tears occurs in the posterior aspect of the labrum, likely due to
the frequent practice in that country of squatting or sitting on the ground or floor.
• Criteria for tears on MR arthrography (MRA) include (fig. 2, 3 and 4):
1.
2.
3.
4.
Contrast extending into the labrum or acetabular/ labral interface
Blunted appearance
Displacement/detachment from underlying bone
Presence of a paralabral cyst
Page 12 of 65
Fig.: Fig. 2) Coronal T2 GRE- weighted image demonstrates the articular fluid
extending into the acetabular/labral interface (arrow). The labrum is flattened and
detached from the underlying bone. These findings are suggestive of a labral tear.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Page 13 of 65
Fig.: Fig. 3) Axial T1-weighted MR arthrography image shows contrast material
extending into the acetabular/labral interface, with a complete detachment of the
labrum from the acetabular rim (arrow), findings suggestive of a labral tear. A synovial
pit is also seen in the anterior junction of the head and neck of the femur (circle). These
finding is frequently associated with situations of femoro-acetabular impingement, one
of the major causes of labral tears.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Page 14 of 65
Fig.: Fig. 4) Sagittal STIR-weighted image shows complete detachment of the anterior
labrum (blue arrow), and a small paralabral cyst (white arrow). These findings are
diagnostic for a labral tear. This patient also has signs of AVN of the femoral head.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Pitfalls in the Evaluation of the Labrum
• It was documented that patients visited, on the average, 3.3 health-care providers
before being correctly diagnosed with a labral tear and more importantly, 33% received
an alternate diagnosis prior to being diagnosed with a labral tear.
• Studies have compared MRA with surgical findings and have shown a range of
sensitivity from 60% to 100% and that of specificity from 44% to 100% for acetabular
labral pathology.
Page 15 of 65
• It is obvious that some labral tears may not be visualized on MRA, but it is less evident
why false-positive MR arthrograms occur. The presence of normal anatomic variants is
the probable explanation for an important number of false-positive MR findings in some
of the previous published studies.
1. Variations in Labral Shape and Signal Intensity
• Asymptomatic subjects can present sometimes with variations from the triangular
shaped and low signal intensity acetabular labrum resulting in a potential imaging pitfall
of tear overdiagnosis.
• Round, irregular and flattened labrum has been reported in people without hip pain (fig.
5 and 6).
Fig.: Fig. 5) Coronal STIR-weighted image demonstrates mild increase of the
interstitial signal of the anterior labrum, without other signs that suggest the presence
of a tear.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Page 16 of 65
Fig.: Fig. 6) Coronal T1-weighted MR arthrography image shows a rounded labrum,
without signs of tear.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
• Focal intermediate to slightly high signal intensity may be seen inside the labrum (fig.
7) or at the labral base.
Page 17 of 65
Fig.: Fig. 7) Coronal T1-weighted MR arthrography image demonstrates a flattened
labrum with increased interstitial signal.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
• These variations of the labral shape and signal intensity are more common in older
patients and in the antero-superior labrum (weight-bearing area).
2. Acetabular Cartilage Undercutting the Labrum
• Cartilage undercutting the labrum can mimic high-intensity signal from a labral tear (fig.
8).
Page 18 of 65
Fig.: Fig. 8) Coronal STIR-weighted image demonstrates a linear high signal under the
base of the anterosuperior labrum (arrow). Is this a tear? Is this cartilage undercutting
the labrum? Is not always easy to make this distinction without articular contrast. There
is no labral tear in this patient.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
• Contrast material in the joint may avoid this pitfall because the contrast material and
cartilage are of different signal intensities (fig. 9 and 10).
Page 19 of 65
Fig.: Fig. 9) Coronal T1-weighted MR arthrography image where is easy to see that
the linear high signal under the base of the labrum (arrow) is not as high as the signal
of the contrast material. This is only cartilage undercutting the labrum.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Page 20 of 65
Fig.: Fig. 10) Coronal T1-weighted MR arthrography image where is easy to see the
linear high signal under the base of the labrum (arrow) presenting with the same signal
intensity of the contrast material. This is not cartilage undercutting the labrum, this is a
labral tear.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
3. Iliopsoas Tendon Crossing the Labrum
Page 21 of 65
• The iliopsoas tendon crosses anterior to the anterior labrum. It is important to
understand this relationship because the high signal between these two low signal
structures may mimic a tear of the labrum (fig. 11).
Fig.: Fig. 11) Axial T1-weighted image showing the iliopsoas tendon (blue arrow)
crossing the anterior labrum (white arrow). Inbetween these two structures is a line of
high signal that should not be mistaken by a labral tear.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Page 22 of 65
• This pitfall can be easily avoided following the iliopsoas tendon proximally to the
muscular component or distally to the insertion in the lesser trochanter (fig. 12).
Fig.: Fig. 12) Axial T2 GRE-weighted images, show the iliopsoas tendon (blue arrow)
crossing the anterior labrum (white arrow) (a). It is easy to follow the iliopsoas tendon
proximally to the muscular component (b) or distally to the insertion in the lesser
trochanter (c).
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
4. Labroligamentous Sulcus
• A normal cleft/sulcus is frequently observed at the junction of the anterior labrum with
the transverse ligament (fig. 13 and 14. See also fig. 18).
Page 23 of 65
Fig.: Fig. 13) Sagittal T1-weighted MR arthrography image obtained at the level of
transverse ligament and anterior labral junction shows the normal labroligamentous
sulcus (arrow) that may be mistaken for a labral tear.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Page 24 of 65
Fig.: Fig. 14) Axial T2 GRE-weighted image where is possible to see the normal
labroligamentous sulcus (arrow) at the junction of the anterior labrum with the
transverse ligament.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Page 25 of 65
• The sulcus at the anterior labral-ligamentous junction is frequently accompanied by
a periligamentous recess located anterior to the ligamentum teres and medial to the
anterior portion of the transverse ligament (fig. 15).
Page 26 of 65
Fig.: Fig. 15) Axial STIR-weighted image shows the normal periligamentous recess
(arrow) inferiorly to the junction of the anterior labrum with the transverse ligament.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
• This normal finding is located more inferior than most anterior labral tears and should
not be misinterpreted as a traumatic anteroinferior labral-ligamentous detachment.
5. Labrocapsular Recess
• The hip articular capsule inserts directly to the anterior and posterior labrum, but
superiorly it inserts in the bony acetabulum creating a high signal labrocapsular recess
that can be similar to a labral tear (fig. 16, 17 and 18).
Page 27 of 65
Fig.: Fig. 16) Coronal STIR-weighted image where is easy to distinguish the labrum
(white arrow), the superior capsule (dark blue arrow) and the labrocapsular recess
(light blue arrow) that should not be mistaken by a labral tear.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Page 28 of 65
Fig.: Fig. 17) Coronal T2 GRE-weighted image where is also possible to distinguish
the labrum (white arrow), the superior capsule (dark blue arrow) and the labrocapsular
recess (light blue arrow).
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Page 29 of 65
Fig.: Fig. 18) Coronal T1-weighted MR arthrography where is possible to see the
labroligamentous sulcus (dark blue arrow), the labrocapsular recess (light blue arrow)
and an antero-superior labral tear (white arrow).
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Page 30 of 65
• Following the inferior and lateral extension of the capsule to the femur allow us to
distinguish the superior capsule from a labral fragment, avoiding this pitfall.
6. Sublabral Recess
• A sublabral recess is a frequent finding that should be considered when we see partial
separation of the labrum from the underlying cartilage (fig. 19, 20 and 21). As discussed
previously this criteria is also used to diagnosis a labral tear. So, to avoid this major cause
of pitfalls, we should be aware of some evidences:
• Sublabral recesses have been described in the anterior and posterior labrum. However,
outside the Japanese population, tears of the posterior labrum are very rare, and usually
not seen unless there is a history of posterior hip dislocation. In view of this, the radiologist
can consider a cleft in the posterior labrum as a sublabral sulcus in virtually all cases.
• In the anterior labrum, recesses are most commonly located anteroinferiorly in 8-o'clock
position. Torn labrum is more frequently found at anterosuperior location in 10- and 11o'clock positions.
• Recesses do not extend into the substance of the labrum or through the full thickness
of the labral base. Unlike the shoulder, where a normal sublabral foramen has been
identified at the anterosuperior quadrant of the glenoid, a sublabral foramen has not
been convincingly shown in the hip.
• Usually a recess is associated with linear sublabral contrast material interposition with
a sharply defined labrum.
• To diagnosis a recess we should not see abnormal signal intensity of the labrum,
cartilage lesions, osseous abnormalities or ganglion cysts.
Page 31 of 65
Fig.: Fig. 19) Axial T1-weighted MR arthrography showing a partial separation of
the posterior labrum from the underlying cartilage (arrow), suggestive of a sublabral
recess.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Page 32 of 65
Fig.: Fig. 20) Axial T1-weighted MR arthrography showing another sublabral recess
(arrow) of the posterior labrum.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Page 33 of 65
Fig.: Fig. 21) Axial T1-weighted MR arthrography reveals a sublabral recess (arrow) of
the posterior labrum that is deeper than the previous ones, but still not extending into
the substance of the labrum or through the full thickness of the labral base.
References: M. Castro; Radiology, Hospital de São João, Porto, PORTUGAL
Images for this section:
Page 34 of 65
Fig. 1: Fig. 1) Axial (a), coronal (b) and sagittal (c) T1-weighted MR arthrography images
show the normal labrum (circles) as a low signal triangular structure and the transverse
ligament (arrows) connecting the anterior and posterior labrum.
Page 35 of 65
Fig. 2: Fig. 2) Coronal T2 GRE- weighted image demonstrates the articular fluid
extending into the acetabular/labral interface (arrow). The labrum is flattened and
detached from the underlying bone. These findings are suggestive of a labral tear.
Page 36 of 65
Fig. 3: Fig. 3) Axial T1-weighted MR arthrography image shows contrast material
extending into the acetabular/labral interface, with a complete detachment of the labrum
from the acetabular rim (arrow), findings suggestive of a labral tear. A synovial pit is also
seen in the anterior junction of the head and neck of the femur (circle). These finding is
frequently associated with situations of femoro-acetabular impingement, one of the major
causes of labral tears.
Page 37 of 65
Fig. 4: Fig. 4) Sagittal STIR-weighted image shows complete detachment of the anterior
labrum (blue arrow), and a small paralabral cyst (white arrow). These findings are
diagnostic for a labral tear. This patient also has signs of AVN of the femoral head.
Page 38 of 65
Fig. 5: Fig. 5) Coronal STIR-weighted image demonstrates mild increase of the interstitial
signal of the anterior labrum, without other signs that suggest the presence of a tear.
Page 39 of 65
Fig. 6: Fig. 6) Coronal T1-weighted MR arthrography image shows a rounded labrum,
without signs of tear.
Page 40 of 65
Fig. 7: Fig. 7) Coronal T1-weighted MR arthrography image demonstrates a flattened
labrum with increased interstitial signal.
Page 41 of 65
Fig. 8: Fig. 19) Axial T1-weighted MR arthrography showing a partial separation of the
posterior labrum from the underlying cartilage (arrow), suggestive of a sublabral recess.
Page 42 of 65
Fig. 9: Fig. 20) Axial T1-weighted MR arthrography showing another sublabral recess
(arrow) of the posterior labrum.
Page 43 of 65
Fig. 10: Fig. 18) Coronal T1-weighted MR arthrography where is possible to see the
labroligamentous sulcus (dark blue arrow), the labrocapsular recess (light blue arrow)
and an antero-superior labral tear (white arrow).
Page 44 of 65
Fig. 11: Fig. 17) Coronal T2 GRE-weighted image where is also possible to distinguish
the labrum (white arrow), the superior capsule (dark blue arrow) and the labrocapsular
recess (light blue arrow).
Page 45 of 65
Fig. 12: Fig. 16) Coronal STIR-weighted image where is easy to distinguish the labrum
(white arrow), the superior capsule (dark blue arrow) and the labrocapsular recess (light
blue arrow) that should not be mistaken by a labral tear.
Page 46 of 65
Fig. 13: Fig. 15) Axial STIR-weighted image shows the normal periligamentous recess
(arrow) inferiorly to the junction of the anterior labrum with the transverse ligament.
Page 47 of 65
Fig. 14: Fig. 14) Axial T2 GRE-weighted image where is possible to see the normal
labroligamentous sulcus (arrow) at the junction of the anterior labrum with the transverse
ligament.
Page 48 of 65
Fig. 15: Fig. 13) Sagittal T1-weighted MR arthrography image obtained at the level
of transverse ligament and anterior labral junction shows the normal labroligamentous
sulcus (arrow) that may be mistaken for a labral tear.
Page 49 of 65
Fig. 16: Fig. 12) Axial T2 GRE-weighted images, show the iliopsoas tendon (blue
arrow) crossing the anterior labrum (white arrow) (a). It is easy to follow the iliopsoas
tendon proximally to the muscular component (b) or distally to the insertion in the lesser
trochanter (c).
Page 50 of 65
Fig. 17: Fig. 11) Axial T1-weighted image showing the iliopsoas tendon (blue arrow)
crossing the anterior labrum (white arrow). Inbetween these two structures is a line of
high signal that should not be mistaken by a labral tear.
Page 51 of 65
Fig. 18: Fig. 8) Coronal STIR-weighted image demonstrates a linear high signal under
the base of the anterosuperior labrum (arrow). Is this a tear? Is this cartilage undercutting
the labrum? Is not always easy to make this distinction without articular contrast. There
is no labral tear in this patient.
Page 52 of 65
Fig. 19: Fig. 9) Coronal T1-weighted MR arthrography image where is easy to see that
the linear high signal under the base of the labrum (arrow) is not as high as the signal of
the contrast material. This is only cartilage undercutting the labrum.
Page 53 of 65
Fig. 20: Fig. 10) Coronal T1-weighted MR arthrography image where is easy to see the
linear high signal under the base of the labrum (arrow) presenting with the same signal
intensity of the contrast material. This is not cartilage undercutting the labrum, this is a
labral tear.
Page 54 of 65
Fig. 21: Fig. 21) Axial T1-weighted MR arthrography reveals a sublabral recess (arrow)
of the posterior labrum that is deeper than the previous ones, but still not extending into
the substance of the labrum or through the full thickness of the labral base.
Page 55 of 65
Conclusion
• The knowledge of the pitfalls of the MR imaging in the evaluation of the acetabular
labrum are the main way to increase the specificity of the diagnosis of labral tears.
Images for this section:
Page 56 of 65
Fig. 1: Fig. 16) Coronal STIR-weighted image where is easy to distinguish the labrum
(white arrow), the superior capsule (dark blue arrow) and the labrocapsular recess (light
blue arrow) that should not be mistaken by a labral tear.
Page 57 of 65
Fig. 2: Fig. 7) Coronal T1-weighted MR arthrography image demonstrates a flattened
labrum with increased interstitial signal.
Page 58 of 65
Fig. 3: Fig. 13) Sagittal T1-weighted MR arthrography image obtained at the level of
transverse ligament and anterior labral junction shows the normal labroligamentous
sulcus (arrow) that may be mistaken for a labral tear.
Page 59 of 65
Fig. 4: Fig. 15) Axial STIR-weighted image shows the normal periligamentous recess
(arrow) inferiorly to the junction of the anterior labrum with the transverse ligament.
Page 60 of 65
Personal Information
Miguel Henriques Castro
Radiology Department / Hospital de São João / Oporto Medical School / Portugal
Department Director: Prof. Isabel Ramos
[email protected]
Images for this section:
Fig. 1: Porto
Page 61 of 65
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Images for this section:
Page 63 of 65
Fig. 1: Fig. 18) Coronal T1-weighted MR arthrography where is possible to see the
labroligamentous sulcus (dark blue arrow), the labrocapsular recess (light blue arrow)
and an antero-superior labral tear (white arrow).
Page 64 of 65
Page 65 of 65