AJR 2000; 175:646-648
© American Roentgen Ray Society
Unilateral Glenoid Hypoplasia
Unusual Findings on MR Arthrography
Muhammad Munshi1 and
James M. Davidson
1
Both authors: Department of Radiology, University of Manitoba, St. Boniface
General Hospital, 409 Tache Ave., Winnipeg, Manitoba, R2H 2A6 Canada.
Received November 29, 1999;
accepted after revision February 2, 2000.
Presented at the annual meeting of the American Roentgen Ray Society, New
Orleans, May 1999.
Address correspondence to J. M. Davidson.
Introduction
Glenoid hypoplasia or dysplasia of the scapular neck is a congenital
anomaly typified by incomplete ossification of the lower two thirds of the
glenoid and adjacent scapula. More than 100 cases are now reported in the
literature [1,
2]. Only a few cases using MR
imaging have, to our knowledge, been described
[3,4,5],
and no previous reports of MR arthrography in such patients were found.
Additional reported findings include widening of the glenohumeral joint space,
labral hypertrophy, hyperplasia of the coracoid process and acromion, hooking
of the distal clavicle, and hypoplasia of the humeral head. Glenoid hypoplasia
is usually bilateral and symmetric with only six cases described in which the
findings were unilateral [2,
6]. Although often
asymptomatic, patients may present with pain, stiffness, and decreased range
of motion. Instability and humeral head subluxation are uncommon. We present
two cases with unusual imaging findings on MR arthrography.
Case Report 1
A 41-year-old man presented with pain and weakness of the right shoulder.
No history of significant trauma or other musculoskeletal symptoms was noted.
Conventional radiographs of the right shoulder revealed decreased ossification
of the inferior glenoid and adjacent scapular neck
(Fig. 1A). Comparison with the
contralateral shoulder showed hypoplasia of the humeral head. The inferior
glenoid showed a notched appearance with widening of the inferior glenohumeral
joint space. These findings were consistent with glenoid hypoplasia.
Radiography of the left shoulder failed to reveal any evidence of osseous
hypoplasia. After obtaining informed consent, we injected approximately 15-20
mL of diluted (1:250) gadopentetate dimeglumine (Berlex Canada, Lachine,
Quebec, Canada) into the glenohumeral joint with fluoroscopic guidance. Then
we performed MR imaging on a 1.5-T scanner (Symphony; Siemens, Erlangen,
Germany). MR arthrography confirmed complete osseous hypoplasia of the entire
posterior glenoid and scapular neck (Fig.
1B). The osseous elements were replaced by tissue of heterogeneous
signal intensity on both T1-weighted fat-suppressed and fast low-angle shot
(FLASH) sequences. A prominent triangular area of low signal intensity on both
sequences was seen bordering the posterior articular surface, consistent with
hypertrophy of the posterior glenoid labrum. FLASH images showed separation of
the posterior labrum from the adjacent bony glenoid by tissue hypointense to
muscle and continuous with the overlying articular cartilage
(Fig. 1C). The remainder of the
posterior scapular neck consisted predominantly of tissue hypointense to
muscle and similar in signal intensity to that of cartilage. Isolated foci of
increased signal intensity were also seen in the posterior scapular neck
possibly because of extension of intraarticular contrast material. The
anteroinferior bony glenoid was hypoplastic and replaced by prominent tissue
isointense to cartilage on FLASH and T1-weighted fat-suppressed images
(Fig. 1D). A partial thickness
tear of the supraspinatus tendon was also identified. Incidental note was made
of hypertrophy of the coracoid process.
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Fig. 1B. —41-year-old man with pain and weakness of right shoulder. Fast
low-angle shot (FLASH) coronal MR arthrogram at level of posterior joint shows
osseous hypoplasia of entire posterior glenoid (arrow).
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Fig. 1C. —41-year-old man with pain and weakness of right shoulder. FLASH
axial MR arthrogram shows complete osseous hypoplasia of posterior glenoid and
scapular neck. Note hypertrophy of posterior glenoid labrum (curved white
arrow), separated from adjacent bony glenoid by tissue hypointense to
muscle (straight white arrow) and continuous with overlying articular
cartilage. Remainder of posterior scapular neck is also hypointense to muscle
(black arrow) and similar in signal intensity to cartilage.
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Fig. 1D. —41-year-old man with pain and weakness of right shoulder.
T1-weighted fat-suppressed coronal oblique MR arthrogram shows hypoplasia of
anteroinferior bony glenoid, which is replaced by prominent soft tissue
isointense to cartilage (curved arrow). Note partial thickness tear
of supraspinatus tendon (straight arrow).
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Case Report 2
Our other patient was a 67-year-old woman with pain and decreased range of
motion of the right shoulder. No history of significant trauma or other
musculoskeletal symptoms was found. Conventional radiographs of the right
shoulder revealed decreased ossification and notching of the inferior glenoid
consistent with glenoid hypoplasia. Bony hypoplasia was not shown on
radiographs of the left shoulder. MR arthrography confirmed the presence of
osseous hypoplasia of the posterior and anteroinferior bony glenoid, with the
bony elements replaced by tissue of heterogeneous signal intensity on FLASH
sequences. In this patient, the posterior glenoid labrum was separated from
the underlying bone by contrast material that extended into the abnormal
tissue (Fig. 2A). This tissue
was predominantly hypointense to muscle and similar to that of the overlying
articular cartilage on FLASH images. Compared with the findings of the first
patient, the region of the posterior scapular neck clearly showed contrast
material-filled defects consistent with fissuring in the abnormal tissue
(Fig. 2B). The hypoplastic
anteroinferior bony glenoid was replaced by prominent tissue isointense to
that of cartilage on FLASH images, similar to that of the first patient. A
full-thickness tear of the supraspinatus tendon was also identified.
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Fig. 2A. —67-year-old woman with pain and decreased range of motion of right
shoulder. Fast low-angle shot (FLASH) axial MR arthrogram reveals complete
osseous hypoplasia involving posterior glenoid and scapular neck. Posterior
glenoid labrum (curved white arrow) is separated from underlying bone
by diluted gadolinium contrast material (straight white arrow) that
extends posteriorly into area of abnormal tissue. Tissue is predominantly
hypointense to muscle and similar in signal intensity to cartilage (black
arrow).
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Fig. 2B. —67-year-old woman with pain and decreased range of motion of right
shoulder. FLASH axial MR arthrogram obtained just superior to A shows
heterogeneous signal intensity in region of posterior scapular neck. Note
globular areas of high signal intensity (arrow) consistent with
extension of diluted gadolinium into abnormal tissue.
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Discussion
The precise pathogenes of glenoid hypoplasia has not been identified. Most
of the scapula is formed by intramembranous ossification from at least eight
centers. The scapula begins to ossify by the eighth postovulatory week. At
birth, although most of the scapula is ossified, the acromion, coracoid
process, glenoid, vertebral border, and inferior angle of the scapula are
cartilaginous. The bony glenoid fossa develops from two secondary centers of
ossification. A more superior subcoracoid center develops at age 10 and fuses
by about age 15. Near puberty, the inferior secondary glenoid center appears
as a horseshoe-shaped epiphysis. As it grows, the glenoid fossa deepens.
Arrest of any of these normal developmental processes can result in
hypoplasia.
Reports from the literature indicate that although the bony element of the
inferior glenoid may be lacking, the cartilage is preserved and in fact
thickened [4]. This feature
suggests that the bony glenoid that has not developed consists of cartilage
that has failed to ossify. Arrest of ossification of the inferior glenoid
apophysis is implicated. The precise cause of this lack of ossification is not
clear. Previous reports of familial cases suggest that glenoid hypoplasia may
be the result of a low-penetrance dominant gene
[7]. However, this cause has
not been confirmed.
We described the imaging findings of two patients with radiographic
findings consistent with unilateral glenoid hypoplasia. The MR arthrographic
findings reveal hypoplasia of the anteroinferior bony glenoid and severe bony
hypoplasia of the entire posterior glenoid and scapular neck with osseous
elements replaced by tissue of heterogeneous signal intensity. These latter
findings, particularly the severity of hypoplasia of the entire posterior
scapular neck, have not been previously described, to our knowledge, and may
represent unusual variants of glenoid hypoplasia. The signal characteristics
of the tissue replacing the bony glenoid and scapular neck are similar to
those of articular cartilage. This similarity, combined with contiguous
extension of cartilage into the region of abnormal tissue posteriorly in
patient number one, suggests that the replaced tissue may represent cartilage
that has failed to ossify. The severe hypoplasia of the entire posterior
glenoid, including the superior aspect, implies that arrest of the inferior
glenoid apophysis is not the sole abnormality. An additional or an altogether
different abnormality of the normal developmental process must be
implicated.
At least one case we have presented clearly showed extension of
intraarticular contrast material into the abnormal tissue, consistent with
fissuring of probable unossified cartilage. Two cases of similar findings in
patients with glenoid hypoplasia have been reported. In one reported case,
late filling of a small channel of contrast material on arthrography was seen
in the initially unopacified space between the humeral head and the glenoid
[8]. This late filling was
thought to be caused by either developmental or acquired ulceration of the
articular cartilage. Increased shear force during abnormal posterior movement
of the humeral head in these patients may be a contributing factor. Splitting
or ulceration of the joint surface is described in another patient on CT
arthrography [9].
We described two patients with severe hypoplasia of the entire posterior
scapular neck with labral and probable cartilaginous hypertrophy on MR
arthrography. The severity of these findings has been previously unreported
and represents an unusual variant of unilateral glenoid hypoplasia. A recent
increase in case reports of glenoid hypoplasia suggests that it may be more
prevalent than previously thought. The future increased use of MR arthrography
may lead to more frequent diagnosis, enhancing our understanding of this
anomaly and its variants.
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Introduction
Case Report 1
