DOI:10.2214/AJR.07.3523
AJR 2008; 190:W376-W377
© American Roentgen Ray Society
Undersurface Acromial Osteophyte or Deltoid Tendon Attachment to the Acromion?
Michael Kramer
Sumner Radiology, Gallatin, TN
WEB—This is a Web exclusive article.
I read with great interest and enjoyed the article by Hambly et al.
[1] in the November 2007 issue
of AJR, which has excellent examples of the correlation between
subacromial subdeltoid bursography and MRI in regard to shoulder impingement
syndrome. However, I disagree with the legend of
Figure 3B of that article
(Figs. 1A and
1B), which states the solid
white arrow is pointing to an undersurface acromial "osteophyte."
As an aside, most musculoskeletal radiologists use the term "subacromial
enthesophyte," rather than subacromial osteophyte because the bone under
the acromion is originating from a ligament or tendon attachment and not the
lateral margin of the joint. Whether Hambly et al.
[1] had labeled the solid white
arrow in Figure 1B an
enthesophyte or an osteophyte, I believe they would have been incorrect.
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Fig. 3 —Note the downward extension of marrow into a subacromial
enthesophyte (arrow) on a T-weighted oblique coronal MR image
(Reprinted with permission from Steinbach LS, Tirman PFJ, Peterfy CG, Feller
JF. Shoulder magnetic resonance imaging. Philadelphia, PA:
Lippincott-Raven, 1998:107-108
[2])
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Fig. 1A —46-year-old woman with inflammatory changes in
acromioclavicular joint with osteophyte formation, secondary impingement, and
bursitis (grade 2). Symptom duration was 4 months, and patient reported
complete resolution of symptoms after 6 months of follow-up. Subacromial
bursogram shows inflammatory changes in acromioclavicular joint.
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Fig. 1B —46-year-old woman with inflammatory changes in
acromioclavicular joint with osteophyte formation, secondary impingement, and
bursitis (grade 2). Symptom duration was 4 months, and patient reported
complete resolution of symptoms after 6 months of follow-up. Coronal oblique
STIR MR image (TR/TE, 2,000/20; inversion time, 160 milliseconds; echo-train
length, 8) shows changes in acromioclavicular joint (open arrow) with
osteophyte formation (closed arrow). Reprinted from Hambly N,
Fitzpatrick, P, MacMahon P, Eustace S. Rotator cuff impingement: correlation
between findings on MRI and outcome after fluoroscopically guided subacromial
bursography and steroid injection. AJR 2007; 189:1179-1184
[1])
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Fig. 2 —Low signal intensity structure under the distal acromion
represents the normal insertion of the deltoid tendon (arrow). This
can be mistaken for an enthesophyte. (Reprinted with permission from Steinbach
LS, Tirman PFJ, Peterfy CG, Feller JF. Shoulder magnetic resonance
imaging. Philadelphia, PA: Lippincott-Raven, 1998:107-108
[2])
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This solid white arrow is located at the lateral aspect of the acromion.
What this arrow is actually pointing to is a nor mal variant, which is often
confused with a subacromial enthesophyte. Some radiologists believe it
represents a tendon slip of the deltoid muscle attaching to the acromion
[2,
3]
(Fig. 2), whereas others
believe it represents the coracoacromial ligament insertion on the acromion
[4]. In either case, this
low-signal structure below the acromion is often misinterpreted as an
undersurface acromial enthesophyte by radiologists reviewing shoulder MRI.
This is a common mistake made in musculoskeletal radiology and could lead to
unnecessary surgery for shoulder impingement syndrome
[4].
An undersurface acromial enthesophyte should have the same marrow signal as
the bone above it (Fig 3). Even
though Figure 1B is a STIR
image, the area in question represented by the solid white arrow has a much
lower (darker) signal than the acromion bone marrow. Also the arthrography
radio graph in Figure 1A shows
no bone excrescence arising from the undersurface of the acromion.
The inflammatory changes in the subacromial subdeltoid bursae are thus
likely a response to the hypertrophic or degenerative changes on the
undersurface of the acromioclavicular joint. The solid white arrow in
Figure 1B represents the
deltoid origin or coracoacromial ligament proximal attachment to the acromion.
This structure should not contribute to subacromial sub deltoid bursitis on
the arthrogram or the MRI.
Acknowledgments
I thank Robert Lopez, Department of Radiology at the University of Alabama
at Birmingham, for his guidance and encouragement in helping me, a private
practice radiologist, write this letter to the AJR. In addition, I
thank Lynn Steinbach, Department of Radiology at the University of California,
San Francisco, for allowing me to reprint two figures from her book,
Shoulder Magnetic Resonance Imaging.
References
- Hambly N, Fitzpatrick, P, MacMahon P, Eustace S. Rotator cuff
impingement: correlation between findings on MRI and outcome after
fluoroscopically guided subacromial bursography and steroid injection.
AJR 2007; 189:1179
-1184[Abstract/Free Full Text]
- Steinbach LS, Tirman PFJ, Peterfy CG, Feller JF.
Shoulder magnetic resonance imaging. Philadelphia, PA:
Lippincott-Raven, 1998:107
-108
- Kaplan, PA, Bryans KC, Davick JP, Otte M, Stinson WW, Dussault RG.
MR imaging of the normal shoulder: variants and pitfalls.
Radiology 1992;184
: 519-524[Abstract/Free Full Text]
- Stoller DW. Magnetic resonance imaging in orthopaedics
and sports medicine, 2nd ed. Philadelphia, PA: Lippincott-Raven,1997
: 624-627
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N. Hambly and S. Eustace
Reply
Am. J. Roentgenol.,
June 1, 2008;
190(6):
W378 - W378.
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