AJR 2002; 179:893-896
© American Roentgen Ray Society
Focal Pulmonary Interstitial Opacities Adjacent to Thoracic Spine Osteophytes
Shoichiro Otake1,
Masashi Takahashi2 and
Takeo Ishigaki3
1 Department of Radiology, Toki Municipal General Hospital, 703-24 Tokitsuguchi,
Tokitsu-cho, Toki, Gifu 509-5193 Japan.
2 Department of Radiology, Shiga University of Medical Science, Ohtsu, Shiga
520-2192 Japan.
3 Department of Radiology, Nagoya University School of Medicine, Nagoya, Aichi
466-8550 Japan.
Received February 6, 2002;
accepted after revision April 5, 2002.
Address correspondence to S. Otake.
Abstract
OBJECTIVE. The purpose of our study was to determine whether
osteophytes of the thoracic vertebrae cause focal fibrosis in the subpleural
region.
CONCLUSION. Osteophytes of the thoracic vertebrae appear to cause
focal fibrosis in the adjacent pulmonary tissue.
Introduction
Osteophytes of the vertebrae develop with degenerative spondylosis. In the
thoracic spine, osteophytes often form on the right side anterior to the
vertebrae [1]. On CT images of
the chest, a focal interstitial opacity is sometimes revealed in the
subpleural region of the lower lobe of the right lung adjacent to the
osteophyte. To our knowledge, this finding and its cause have not been well
described.
The purpose of our study was to determine whether osteophytes of the
thoracic vertebrae cause focal fibrosis in the subpleural region. We assessed
the relationship among the focal interstitial opacity, the osteophyte, and the
patient's age; examined the reversibility of the change by imaging the patient
in the prone position; and correlated the CT findings with histology in
postmortem cases.
Materials and Methods
Review of CT Images Obtained with Patients in Supine Position
We reviewed chest CT images of patients who were examined at Toki Municipal
General Hospital between 1998 and 2000. We selected the first 100 patients
that showed osteophytes of the lower thoracic vertebrae with a thickness of
more than 5 mm on axial CT images. This group included 68 men and 32 women
(age range, 45-85 years; mean ± SD, 69 ± 9 years).
To exactly match the sex distribution and age range of cases in our study,
we reviewed CT images of patients whose sex and age matched those of patients
with osteophytes and selected 100 patients without osteophytes as a control
group. Therefore, the control group also included 68 men and 32 women (ages
range, 45-85 years; mean ± SD, 69 ± 9 years). The patients whose
CT images revealed abnormalities in addition to focal interstitial opacities
adjacent to the osteophytes or who had histories of pulmonary diseases were
excluded from our study. CT scans of 200 patients obtained in the supine
position were retrospectively reviewed.
Prospective CT Study Performed with Patients in Prone Position
To determine whether focal interstitial opacity was dependent on gravity,
CT examinations were prospectively performed from April to May 2001, with
patients in the prone position in seven consecutive patients (two men and five
women; age range, 57-89 years; mean ± SD, 71 ± 11 years). The
patients had osteophytes with a thickness of more than 5 mm and focal
interstitial opacities adjacent to the osteophytes. Informed consent was
obtained from all patients before enrollment in the study, which was approved
by the institutional review committee.
Histologic Correlation in Postmortem Cases
To correlate CT findings with histology, we obtained specimens of the right
lungs from five patients with osteophytes having a thickness of more than 5 mm
and focal interstitial opacities adjacent to the osteophytes from autopsies of
patients who had died in 2000 and 2001. This group included four men and one
woman (age range, 69-84 years; mean ± SD, 76 ± 6 years). H and
E, azan, and elastica Masson stains were used to examine the specimens.
CT Protocol
CT was performed with a helical CT scanner (Xvision/GX; Toshiba Medical
Systems, Tokyo, Japan) using the following parameters: 120 kV; 200 mA; width
of X-ray beam, 10 mm; table speed, 10 mm/sec; breath-hold after full
inspiration for one scan, 8 sec; number of scans required to cover the entire
lungs, 4; section thickness, 10 mm; section interval, 10 mm; field of view,
320 mm; reconstruction matrix, 512x512; bone algorithm, window center of
-500 H and window width of 1600 H. CT images were analyzed by two
board-certified radiologists who were experienced in interpreting chest CT
scans. Final interpretation of all CT images was determined by consensus.
Statistical Analysis
The relationship among focal interstitial opacity, presence and thickness
of the osteophyte, and patient's age was assessed by using a chi-square test.
A p value of less than 0.05 was considered statistically
significant.
Results
Incidence of Focal Interstitial Opacities
Osteophytes were present in the right anterior portions of the lower
thoracic vertebrae in all 100 patients with osteophytes. Focal interstitial
opacities in the subpleural region adjacent to the osteophytes of the lower
lobe of the right lung were shown in 45 of the 100 cases. The findings of
focal interstitial opacities could be classified morphologically into two
patterns; reticular and linear. The reticular pattern was defined as an
irregular and fine netlike arrangement of interstitial thickening
(Fig. 1), whereas the linear
pattern was defined as an elongated thin or thick line parallel to the pleural
surface (Fig. 2). Cases with
both patterns were classified on the basis of the predominant pattern.
Twenty-six cases showed the reticular pattern and 19 cases showed the linear
pattern. In the control group without osteophytes, no cases showed focal
interstitial opacities. In the group with osteophytes, a significant
difference existed between the presence of the osteophytes and the frequency
of focal interstitial opacities (p<0.001).
The incidence of focal interstitial opacities increased with the thickness
of the osteophytes (Table 1). A
significant difference was found between the thickness of the osteophytes and
the incidence of focal interstitial opacities (p = 0.039). No
significant difference was found between the patient's age and the incidence
of focal interstitial opacities or between the patient's age and the thickness
of the osteophytes.
CT Findings of Patients Imaged in the Prone Position
Of the seven patients in the prospective study, four showed the reticular
pattern and three showed the linear pattern on prior CT performed with the
patient in the supine position. On the CT examinations performed in the prone
position, findings in all seven patients were identical to findings in those
performed in the supine position. These results suggest that these changes
were irreversible (Fig.
3A,3B).
Histologic Findings
Macroscopically, the pleura that was attached to the osteophyte was white
and hard, and a collapse of the alveolar spaces with a relatively uniform
thickness in the subpleural region was seen. In the collapsed area, the
collagen fibers were markedly increased and the elastic fibers were slightly
increased; this finding was consistent with fibrosis (Fig.
4A,4B,4C,4D,4E).
These results were seen in all the five postmortem cases.
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Fig. 4B. —75-year-old man who died from rupture of left common iliac
aneurysm. CT image shows reticular pattern (white arrow) adjacent to
10-mm-thick osteophyte. Note aneurysm of descending aorta (black
arrow).
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Fig. 4C. —75-year-old man who died from rupture of left common iliac
aneurysm. Axial section of gross specimen corresponding to B shows
white change uniformly spreading in subpleural region (arrows).
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Fig. 4D. —75-year-old man who died from rupture of left common iliac
aneurysm. Photomicrograph of histopathologic specimen shows collapse of
alveolar spaces in subpleural region (arrows). (H and
E,x40)
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Fig. 4E. —75-year-old man who died from rupture of left common iliac
aneurysm. Photomicrograph obtained with higher magnification than that shown
in D reveals increase in collagen fibers (asterisks). (Azan
stain,x100)
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Discussion
Osteophytes of the spine are extremely common in spondylosis. By the age of
50 years, osteophytes are seen in approximately 80% of men and 60% of women
[1]. Osteophytes occur
predominantly on the right side of the vertebrae in the thoracic spine because
the descending aorta courses on the left side and its pulsations inhibit bone
production [1]. Consequently,
the osteophyte commonly attaches to the medial side of the lower lobe of the
right lung. On routine chest CT, focal interstitial opacities are often noted
in the right lung adjacent to an osteophyte. However, the relationship between
focal interstitial opacities and osteophytes has not been well examined.
Histologic examination showed that focal interstitial opacity was fibrosis.
On the CT examinations performed with patients in the prone position, focal
interstitial opacities did not disappear, a finding that suggests irreversible
changes. In the retrospective study, focal interstitial opacities were noted
in 45% of the patients with osteophytes; however, none were noted in the
patients without osteophytes. These findigns suggest that the focal
interstitial opacity was caused by direct compression from the osteophyte. A
significant difference was found between the thickness of the osteophyte and
the incidence of focal interstitial opacity. The thick osteophyte seems to
compress the pulmonary tissue severely. These findings suggest that the cause
of focal interstitial opacity is mechanical stress from the osteophyte. On the
other hand, no significant difference between the patient's age and focal
interstitial opacity was seen, possibly because of the lack of significant
difference between the patient's age and the thickness of the osteophyte.
Our study suggests that mechanical compression by the osteophyte causes
focal fibrosis in the adjacent pulmonary tissue. Protrusion of the osteophyte
may also cause the collapse of the subpleural alveolar space chronically and
the subsequent formation of collagen and elastic fibers in the alveolar septa.
In addition, the abnormal blood circulation or abnormal ventilation caused by
the mechanical compression may contribute to fibrosis formation. However,
because it is difficult to fully explain the mechanism of fibrosis, further
studies are needed. An animal model might provide the best means for the
further study.
Both reticular and linear patterns were seen on CT images. No explanation
for the two patterns could be established. The amount of the increased
collagen and elastic fibers and their distribution in the 10-mm section
thickness may be one explanation.
On routine chest CT performed with patients in the supine position,
dependent density is seen in the posterior regions of both lungs as a result
of volume loss in the dependent lung. Dependent density also can be seen in
the anterior portion of the vertebrae. However, such density disappears in
images obtained with patients in the prone position and, therefore, the change
that the density represents is considered reversible
[2]. Focal interstitial
opacities shown in our study did not disappear in the images obtained with
patients in the prone position. This finding that suggests that the changes
are irreversible and different from those in dependent density.
The differential diagnosis includes early interstitial pneumonia, collagen
vascular disease, asbestosis, and chronic pneumonia in the periphery
[3,4,5].
In early interstitial pneumonia and asbestosis, the subpleural curvilinear
shadow is noted bilaterally in the subpleural region. Focal fibrosis in our
study is shown only in the subpleural region adjacent to the osteophyte. The
changes after pneumonia usually show a segmental or subsegmental distribution.
Therefore, the differentiation of focal fibrosis adjacent to the osteophyte
from these diseases is not difficult.
All osteophytes were found on the right side of the lower thoracic
vertebrae in our study. Consequently, focal fibrosis was noted only in the
right lung. If the osteophyte developed on the left side because of the
rightward elongation of the descending aorta, we speculate that focal fibrosis
might form in the left lung.
On the basis of our limited cases, focal fibrosis adjacent to osteophytes
of the thoracic vertebrae appears to be caused by compression from the
osteophyte. This change should not be confused with other types of lung
disorders.
Acknowledgments
We thank Hiroshi Oda for his assistance with the CT examinations, Fumio
Matsubara for his help in the statistical analysis, Hiroaki Ozawa and Fusae
Hayashi for their assistance with histologic correlation, Hitomi Hayashi for
her secretarial assistance, and Phyllis S. Bergman for her editorial
assistance.
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