AJR 2004; 182:173-179
© American Roentgen Ray Society
Helical CT of Rib Lesions: A Pattern-Based Approach
Michel De Maeseneer1,
Johan De Mey1,
Leon Lenchik2,
Hendrik Everaert1 and
Michel Osteaux1
1 Department of Radiology and Nuclear Medicine, Vrije Universiteit Brussel,
Laarbeeklaan 101, 1090 Jette, Belgium.
2 Department of Radiology, Wake Forest University Baptist Medical Center,
Winston-Salem, NC 27157.
Received October 22, 2002;
accepted after revision May 16, 2003.
Address correspondence to M. De Maeseneer.
Introduction
The discovery of a solitary hot spot of the rib on bone scintigraphy is a
common occurrence. In this setting, differentiation between benign rib
fracture and metastatic disease is clinically important. Baxter et al.
[1] found that in patients with
known extraskeletal malignancy, solitary rib lesions are frequently malignant
in origin (41%). Standard radiographs, including spot radiographs, are usually
obtained. CT of the chest using transverse sections also is often performed.
In our experience, however, differentiating benign and malignant conditions on
the basis of these investigations is often difficult. MRI of the rib is not
routinely performed, and with MRI sequences adapted for the visualization of
bone structures, artifacts related to breathing usually pose a problem. In
addition, breath-hold sequences used in body MRI offer insufficient detail for
visualization of bone rib abnormalities.
Because the transverse sections obtained with standard CT technique are
oblique with regard to both the long and the short axes of the rib,
interpretation may be difficult (Fig.
1A,
1B,
1C). Hence, we sought to
develop an improved CT technique for the evaluation of rib lesions. The use of
angulated thin-section helical CT offers the possibility to obtain several CT
sections of any selected rib and to analyze the rib as if one were looking at
a long tubular bone. After the completion of this project, MDCT became
routinely available at our department. Hence, instead of angulating the
gantry, we obtain reconstructions along the long axis of the rib; this
approach yields a similar appearance of the rib as described in this article.
With this technique, evaluating the cortical and intramedullary areas of the
rib is possible. Adjacent soft-tissue masses also can be assessed in detail.
In this article, we describe a pattern-based approach based on the lesions we
encountered in 50 patients.
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Fig. 1A. —50-year-old man with subtle rib fracture. CT image of chest
reveals abnormal area in rib (arrow), but interpretation is difficult
because CT image was obtained in plane nearly perpendicular to long axis of
rib.
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Fig. 1B. —50-year-old man with subtle rib fracture. CT section obtained
with angulated helical CT technique shows rib fracture (arrowhead) is
more easily recognized on CT images obtained along long axis of rib. Also note
small pleural hematoma (arrow).
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Fig. 1C. —50-year-old man with subtle rib fracture. Coronal
reconstruction also allows confident diagnosis of rib fracture (white
arrow). Note presence of intramedullary callus formation (black
arrows).
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Technical Considerations
In 50 patients with a solitary rib lesion detected on technetium-99m bone
scintigraphy, single-detector helical CT was performed with angulation of the
gantry (Somatom 4A, Siemens, Erlangen, Germany). The patient was placed in a
supine position. An anteroposterior scout image was first obtained using a
breath-hold technique (inspiration) without gantry angulation. Care was taken
to ensure precise positioning of the patient in the center of the gantry. On
the basis of the findings on the bone scintigram, the involved rib was
identified on the scout image. When the lesion was located in the posterior
portion of the rib, CT images were obtained without tilting of the gantry. In
contrast, when the lesion was located in the lateral or anterior portion of
the rib, the gantry was tilted 30° anteriorly. CT parameters were as
follows: breath-hold technique (inspiration); slice thickness, 1 mm; pitch, 2;
reconstruction thickness, 1 mm; 120 kVp; 200 mAs; rotation time, 0.75 sec;
matrix size, 512 x 512; and bone algorithm. A typical helical CT
sequence took 10–15 sec to complete (26–40 cm).
In eight patients, a biopsy of the rib was performed using a CT fluoroscopy
technique (slice thickness, 8 mm; rotation time, 0.75 sec). An Ackerman biopsy
set (Cook, Bjaeverskov, Denmark) was used for bone biopsy, whereas an 18-gauge
Terumo biopsy needle (Bauer Medical International, Santo Domingo, Dominican
Republic) was used for soft-tissue biopsy. For biopsy of posterior rib
lesions, patients were placed in a prone position and no gantry angulation was
used. For biopsy of anterolateral rib lesions, patients were placed in a
supine position and the gantry was tilted 30° anteriorly.
An experienced musculoskeletal radiologist in concert with a senior chest
radiologist analyzed the imaging studies. Using a pattern approach (Figs.
2A,
2B,
2C,
2D,
2E,
2F,
2G,
2H and
3A,
3B,
3C,
3D,
3E,
3F), they evaluated the
following criteria: integrity of cortex (fracture, osteolytic pattern),
presence of a soft-tissue mass (involving the rib or adjacent soft tissues),
osteolysis, osteosclerosis, presence of callus, and presence of fracture
fragments.
Imaging and Biopsy Findings
The patients ranged in age from 9 to 79 years (average age, 58 years).
There were 29 female and 21 male patients. The final diagnosis was based on a
follow-up, additional imaging studies, or biopsy (n = 8). The
follow-up consisted of a review by the principal author of the clinical,
pathologic, and imaging files of the patients. The duration of follow-up
varied from 6 months to 2 years (mean, 9 months). A lesion of the rib was
detected in all patients examined with the angulated helical CT technique.
Additional lesions of other ribs that were not depicted on scintigraphy
were evident in five patients. In 14 (28%) of the 50 patients, the rib lesions
were metastatic in origin. The difference with the prevalence reported by
Baxter et al. [1] is most
likely related to selection bias. Metastases were associated with breast,
prostate, colon, and lung neoplasms and with melanomas. In three (6%) of the
50 patients, rib destruction was caused by contiguous spread of lung tumor and
mesothelioma. One patient had a primary rib tumor. In 22 (44%) of the 50
patients, the rib lesions were related to a benign recent or old fracture. Ten
patients (20%) were lost to follow-up, however. Twenty-two (44%) of the 50
patients had a history of extraskeletal malignancy.
Fractures and Fracture Complications
Although the ribs are a common site of abnormality, the CT features of rib
fractures and other pathologic conditions of the rib have received little
attention. Fractures and metastatic disease are the most common conditions
involving the ribs. Primary tumors and infection are rare
[2,
3]. Rib fractures may occur as
a result of blunt chest trauma but also have been reported in relation to
coughing, nervous tic, and participation in certain sports
[4,
5].
When the fracture ends are substantially displaced, diagnosis is usually
possible based on standard radiographs of the ribs or chest radiographs. If
fractures are subtle and non-displaced, standard radiography may appear to
show normal findings despite the presence of clinical symptoms and increased
uptake on bone scintigrams. Angulated helical CT may show pathologic changes
in such cases.
In the case of rib fractures, cortical interruptions may be located to one
or both sides of the cortex. Stress fractures of the rib are uncommon but may
be encountered in patients who participate in certain sports such as golf
(Fig. 4).
Radiographic findings may be negative for fracture in 60% of patients. A
subtle area of bone sclerosis or osteolysis may be evident on CT images
[5–7].
Fractures of the rib may also resemble greenstick fractures with buckling of
one side of the cortex of the rib. In infants with inflicted injury, both
recent and healing fractures may be detected simultaneously. CT may help
detect fracture lines, fracture fragments, callus formation, and pleural
hematoma or pneumothorax (Figs.
5,
6,
7). With fracture healing,
callus formation and residual cortical deformity may be evident. During the
healing phase, fractures may remain active on scintigraphy for months or even
years.
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Fig. 5. —Benign rib fracture in 69-year-old woman with right lung
neoplasm who reported recent fall. CT image shows fracture of seventh rib on
right side. Note small fracture fragment (f) and subpleural hematoma (h).
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Fig. 6. —Rib fracture with callus formation in 76-year-old man. CT
image shows well-defined fracture (arrow) and periosteal callus
formation (c). Follow-up CT (not shown) revealed progressive healing.
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Metastatic Disease, Primary Tumors, and Infection
Metastatic disease is a common cause of rib lesions. In children, secondary
malignant tumors of the rib may be related to metastatic Ewing's sarcoma and
neuroblastoma. In adults, primary tumors of the lung, breast, thyroid, kidney,
prostate, and liver should be considered (Figs.
8A,
8B,
9,
10,
11A,
11B). Sixteen percent of
metastases involve the ribs. In patients with metastatic disease, lytic or
sclerotic lesions may be evident. In advanced cases, rib destruction and
soft-tissue masses may be apparent
[3]. In patients with lung,
abdominal, and pleural neoplasms, the rib adjacent to the tumor may be invaded
by contiguous spread and cortical destruction may be apparent (Fig.
12A,
12B).
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Fig. 8A. —Rib metastasis in 56-year-old man with previous history of
lung carcinoma. CT image shows fracture of left eighth rib. Also note area of
pleural thickening (white arrow). Subtle thinning of outer cortex of
rib (black arrow) is visible. In addition, there is no evidence of
callus formation 4 weeks after onset of symptoms, suggesting that fracture
occurred as result of metastatic disease.
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Fig. 8B. —Rib metastasis in 56-year-old man with previous history of
lung carcinoma. CT image of eighth rib shows well-defined osteolysis of inner
cortex (arrow). Follow-up CT (not shown) revealed progressive
metastatic disease.
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Fig. 9. —Intramedullary lytic lesion in 50-year-old woman with breast
carcinoma. CT image shows moderately well-defined intramedullary lytic lesion
with surrounding area of sclerosis (arrowheads).
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Fig. 11B. —Rib metastasis in 60-year-old woman with breast carcinoma. CT
image shows left-sided small focus of intramedullary sclerosis
(arrow). Follow-up CT (not shown) revealed progressive metastatic
disease.
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Primary benign tumors involving the ribs include fibrous dysplasia,
hemangioma, Langerhans cell histiocytosis, osteoblastoma, enchondroma,
chondromyxoid fibroma, aneurysmal bone cyst, chondroblastoma, osteochondroma,
osteoid osteoma, giant cell tumor, and marrow space hyperplasia
[2,
3,
6,
7]. Usually expansile lytic
lesions are apparent. Certain characteristic features may suggest a specific
type of tumor. A groundglass appearance may be apparent in fibrous dysplasia.
In contradistinction, a trabecular pattern may be seen in hemangiomas, whereas
calcification may be found in osteochondroma
[7]. Nevertheless, biopsy or
surgical excision often will be necessary for the precise diagnosis (Fig.
13A,
13B).
Primary malignant tumors involving the ribs include Ewing's sarcoma and
primary osteosarcoma in children; and chondrosarcoma, multiple myeloma, and
secondary osteosarcoma in adults. In children, primary rib tumors are more
often malignant than benign.
Tuberculosis is the most common infectious lesion of the rib, occurring in
up to 5% of patients with osteoarticular tuberculosis
[8]. In patients addicted to
heroin, however, the rib is the most commonly involved bone. Juxtacortical
soft-tissue masses with peripheral ring enhancement may be evident in these
patients. In patients with actinomycosis, lung and thoracic wall masses may
accompany rib destruction. Infection may lead to an osteolytic pattern, and
periosteal reaction may also be evident on CT images. Differentiation from
malignant rib lesions may occasionally be difficult, although clinical and
laboratory findings will usually aid in differentiating both conditions.
Conclusion
Thin-section helical CT with gantry angulation allows a detailed evaluation
of rib lesions. The ribs can be viewed as if one is looking at a long tubular
bone, and imaging abnormalities can be better analyzed. In this overview, we
have presented a pattern-based approach to the evaluation of rib lesions on CT
images that may help to differentiate various types of abnormality.
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Introduction
Technical Considerations
