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Original Report |
1 Department of Diagnostic Radiology, Gil Medical Center, Gachon Medical School,
Inchoen 405-760, South Korea.
2 Department of Diagnostic Radiology, Kyung Hee University Medical Center, Kyung
Hee University, Hoekidong 1, Dongdaemoon-ku, Seoul 130-702, South Korea.
3 Department of Anatomic Pathology, Kyung Hee University Medical Center, Kyung
Hee University, Seoul 130-702, South Korea.
4 Department of Anatomy, Gachon Medical School, Inchoen 405-760, South
Korea.
Received April 22, 2004;
accepted after revision July 28, 2004.
Address correspondence to K. N. Ryu.
Abstract
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CONCLUSION. Cysts in the posterosuperior portion of the humeral head (the bare area) were located in the lateral humeral head just posterior to the greater tuberosity. These cysts were lined with collagen connective tissue and were connected to the joint spaces. We suggest that these pseudocysts in the posterosuperior portion of the humeral head may be a normal variant rather than being an abnormal change or vascular channel.
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Subchondral cysts occur in many articular diseases. For example, osteoarthritis, rheumatoid arthritis, intraosseous ganglia, neoplastic processes, posttraumatic processes, and calcium pyrophosphate deposition disease all may cause subchondral cysts. In addition, the presence of a cystic area within the humerus and near the rotator cuff insertion is regarded as supportive evidence of a cuff disorder [1]. However, cystic changes in the humeral heads have also been reported in normal shoulders [2-4]. To our knowledge, no histologically proven report has been issued about these cystic changes of the humeral head in normal shoulders without a rotator cuff disorder or articular disease.
The purpose of this study was to describe the appearance of cysts in the posterosuperior portion of the humeral head on MR arthrography and to correlate the MRI findings with the gross and histologic findings in cadavers.
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Subsequently, the nine shoulders were dissected under the supervision of one experienced orthopedic surgeon, who used an anterior approach that was designed to avoid damage to the posterior and lateral portions of the humeral head. After detecting cortical dimples in posterosuperior portions of the humeral heads that were suggestive of cystic lesions on MR images, we selected five humeral heads with clearly visible cystic lesions in the humeral heads. We divided the posterosuperior portion of the humeral head including cortical dimples into five bone segments (an approximately 1-cm3 volume) each. After fixing the bone segments, we divided each segment into undecalcified bone sections (10-mm in thickness) with a soft-tissue cutting machine to avoid damage to soft tissue in or near cysts. Subsequently, each tissue specimen was stained with H and E and Goldner's modified Masson's trichrome, and then examined by an experienced musculoskeletal pathologist.
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MRI Findings
Between one and three cystic lesions (mean, 2.3) were observed in each
humeral head, and the longest of these cystic lesions was about 2-4 mm (mean,
2.56 mm). All lesions were observed as round or oval high-signal-intensity
lesions on T2-weighted and fat-suppressed T1-weighted MR arthrography images.
Also, shoulder joint spaces were filled with contrast medium of high signal
intensity on fat-suppressed T1-weighted images, which established the presence
of connections between joint spaces and cystic lesions of the humeral heads.
All of these cystic lesions were located in lateral humeral heads just
posterior to the greater tuberosity (Figs.
1A and
1B).
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In the humeral heads, there was no significant evidence of degenerative changes such as cortical thinning, cartilage thinning or breakage, subchondral cyst formation, or subchondral bone marrow change on MR images.
Gross Findings
After dissecting the shoulders and opening the joint capsules, we found
small variably sized focal depressions or dimples with round or oval contours
in the posterosuperior portion of the humeral head—the presumed area of
cystic lesion on MRI. These lesions had openings into joint spaces and were
located in the junctions between the humeral heads and the joint capsule
attachments, just posterior to the greater tuberosity. However, the surfaces
of the nearby cartilage in the humeral heads were relatively well preserved
without defect or color change.
Histologic Findings
During histologic examination of five specimens (Figs.
1C and
2), cystic lesions in the
posterolateral portions of humeral heads were found to have connections with
the joint spaces and focal discontinuities of cortical bones with pseudocyst
formations, which had no synovial lining. All cystic lesions were located in
the bare areas of the humeral heads without cartilage coverage. These cystic
lesions had walls of relatively thick collagen fibroconnective tissues and no
inner myxoid content or mucoid material. The inner walls of most lesions
showed no specific cells, except for some cuboidal cells, and there was no
evidence of vascular endothelial cells, macrophages, osteoclasts, or marks due
to hemorrhage. Adjacent to the openings of pseudocysts, no degenerative
changes such as thinning, cracking, or breakage in neighboring cartilage were
observed. The inner trabeculae and the bone marrow also showed normal findings
near pseudocysts.
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MRI-Histologic Findings Correlation
Small cystic lesions filled with contrast medium in the posterosuperior
portions of the humeral heads on the MR arthrographic images corresponded to
pseudocyst formations beneath the cortical bones histologically. These lesions
became connected to the joint spaces, as determined by histologic examination,
just as the contrast medium filled the cystic lesions from the joint spaces as
seen on the MR arthrographic, images. The lesions were not lined with synovium
but rather with collagen fibroconnective tissues. The lesions had focal
cortical defects as their openings, and no degenerative changes were evident
in nearby cortex or cartilage. Overall, the cystic lesions in the
posterosuperior portions of the humeral heads in this study were not
subchondral cysts from degenerative changes, vascular structure, or synovial
cysts.
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Subchondral cysts appear between thickened subchondral trabeculae. Cysts often are multiple and histologically can contain myxoid and adipose tissue, occasional cartilage with surrounding fibrous components, and peripheral sclerotic bone [6]. Resnick et al. [7] applied the term "geodes" to subchondral cysts from osteoarthritis, rheumatoid arthritis, calcium pyrophosphate deposition disease, and osteonecrosis. In degenerative osteoarthritis, proposed theories of the pathogenesis of cyst formation include the bone contusion theory and the synovial fluid intrusion theory. In rheumatoid arthritis, geodes result from inflammatory changes in the synovial lining of the articular cavity creating pannus that extends across the cartilaginous surface and eventually destroys cartilage and bone.
Several studies reported that cystic changes of the greater tuberosity and of the head of the humerus were observed in 50-80% of shoulders with rotator cuff tears [3, 4, 8]. However, cystic changes are also observed in normal shoulders [2-4]. In our experience, small cystic changes are often detected in the humeral heads of normal shoulders without rotator cuff tears.
On the basis of a report by Yoon et al. [9], subchondral cysts in the posterolateral portion of the humeral head were detected in approximately 72% of cases. In addition, about 91% of cysts were connected to the joint cavity. However, in the present study, cystic lesions in the humeral head were presumed to be subchondral cysts without histologic confirmation. Moreover, no detailed differential percentage of cystic change in the humeral head was provided according to abnormal change in the shoulders, such as that due to a rotator cuff tear.
A study was also made of 140 painful shoulders on MRI to determine the relationship between cystic changes of the humeral head and the integrity of the rotator cuff [4]. In that study, cystic changes were observed in 49 (35%) of 140 shoulders, and the most common site was the posterior half of the middle facet of the greater tuberosity. The second most common site was the attachment of the supraspinatus tendon. It was concluded that there are two distinct types of cystic changes: one at the attachment of the supraspinatus and subscapularis, which is closely related to tears of these tendons, and the other in the bare area, which is related to a degenerative aging process from the lack of cartilage coverage.
However, except cystic changes related to rotator cuff tear or degenerative aging process, cystic changes in the humeral heads on MR images can be caused by vascular channels [10]. In this study, dorsolateral vascular channels were found within the bare area of the proximal humerus, and these could be differentiated from cysts seen with partial tears of the supraspinatus and infraspinatus tendons.
Cystic changes close to the bare area of the humerus are viewed as consequences of a degenerative aging process [4], and dorsolateral vascular channels are reported [10] resemble the cystic changes in the posterolateral portion of the humeral head found in our study. However, in our study, these cystic changes showed no inner vascular structure and no evidence of degenerative changes in nearby cartilage or bone, such as thinning of cartilage, breakage of cartilage, or trabecular change. Therefore, these cystic changes were not true cysts but rather pseudocysts.
In summary, cystic lesions are commonly visible in the posterosuperior portions of the humeral heads (the bare areas), just posterior to the greater tuberosity on shoulder MR images. These were found to be focal dimples at gross examination and pseudocysts lined with collagen fibroconnective tissues at histologic examination. These cystic lesions were connected with the joint spaces, and no degenerative change was evident in nearby osteochondral structures. Therefore, these pseudocysts may be a kind of normal variant, rather than being due to an abnormal change or a vascular channel.
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