Work In Progress
WORK IN PROGRESS
Computed Tomographic Diagnosis of Osteomyelitis1
Criteria for the final diagnosis included appropriate clinical history and physical findings, positive blood culture or positive bone aspirate, and subsequent radiographic changes [1].
Jerald P. Kuhn, M.D., and Paul E. Berger,JVI.D. Computed tomography (CT) was performed in conjunction with conventional radiography and radionuclide imaging in 22 children with known or suspected osteomyelitis. Preliminary findings suggest that when radionuclide scans are positive, CT can exclude or establish medullary involvement, differentiate between overlying soft-tissue and underlying bony abnormality, and clearly delineate the anatomy of the soft tissues.
RESULTS Eight patients were found to have primary hematogenous osteomyelitis with medullary involvement; 2 had secondary osteomyelitis with medullary involvement; 3 had secondary osteomyelitis limited to the periosteum or the cortex; 3 had cellulitis; 3 had arthritis or synovitis; and 1 had an osteoid osteoma. Two patients had nondiagnostic scans, 1 because the marrow space was too small to measure and the other because of excessive motion. Soft-tissue anatomy in the extremities of young children can be clearly defined by CT, despite the relative lack of body fat. The cortical and periosteal portions of the bone are generally not as well seen as with conventional radiography, but visibility of the medullary cavity is superior. Tissue densities can be measured in the medullary cavity and are similar for both extremities. In the normal child, these densities tend to be in the negative range and may go as low as -120 Hounsfield units. As the ends of the bones are approached, the density increases in proportion to the amount of cancellous bone. Care must be taken to position the extremities symmetrically so that cuts are not taken of cancellous bone on one side and fatty marrow on the other.
Bones, inflammation. Bones, radionuclide studies, 4[0].1299 • Computed tomography, bone, 4 [0] .1211 • (Skeletal system, osteomyelitis, 4 [0] .210) INDEX TERMS:
Radiology 130:503-506, February 1979
Preliminary findings in children with known or suspected osteomyelitis suggest that computed tomography (CT) can be helpful in the diagnosis of this serious and potentially crippling childhood disease. METHODS AND MATERIALS Twenty-two children ranging in age from 4 months to 16 years had serial radiographs of the affected bones (TABLE I). CT was performed using an Ohio Nuclear Model 50 Delta Scanner with an 8-mm collimator and a scanning time of 2:20 to produce two slices. Patients were examined supine with an elastic bandage around the legs for immobilization. Sedation was used in younger, uncooperative children. Both legs or both arms were scanned simultaneously, with the uninvolved extremity used for comparison. Continuous scans were made of the affected area, while one or two cuts were taken of portions of bone away from the area of involvement. Scanning of humeral lesions was difficult due to respiratory motion. Two patients had nondiagnostic scans, one because of excessive motion and the other because the marrow space was too small to measure. The medullary canals in the small bones of the hands and feet were not as clearly defined as in the larger bones. In some patients, the image had to be magnified to obtain relative density measurements; in one, measurements could not be obtained even with magnification. Radionuclide images were made with a gamma camera in all patients in both early and late stages using 99mTc-pyrophosphate in a dose of 400 p,Ci/kg. Radionuclide scans were obtained on a conventional rectilinear scanner.
CASE REPORTS We present several cases showing the types of abnormal findings and the role CT can play in detecting them. CASE I: A14-year-old boy (G.C.) was seen following five days of fever and right thigh and leg pain. Radiographs of the distal femur were normal but there was a progression to characteristic findings of osteomyelitis. A radionuclide scan on admission showed increased uptake in the distal femoral shaft as well as in the epiphyseal portions of the femur, tibia, and fibula (Fig. 1, A). There was also increased radioactivity in the bones of the right ankle. Both the clinical and the radionuclide findings were consistent with osteomyelitis of the distal femur; the changes in the ankle were thought to be related to hyperemia, but a second focus of infection could not be excluded on the basis of the radionuclide scan alone. CT was performed starting 13 cm above the femoral condyle. Even there, a marked difference could be seen between the medullary densities, with the affected extremity having a greater density than the normal side (Fig. 1, B). This differential persisted as the distal femur was approached, until the cancellous bone of the metaphysis was reached, at which time the densities evened out. No abnormality was seen in the distal tibia. In this patient, CT was able to diagnose extensive medullary abnormality at a stage when the radiograph was normal. The radionuclide image was consistent with osteomyelitis of the femur but also suggested abnormality in the distal tibia. CT confirmed the intramedullary abnormality in the femur but showed no evidence of disease in the tibia. SUbsequent clinical events showed no evidence of disease in the ankle.
TABLE I: FINAL DIAGNOSIS AND POSITIVE FINDINGS BY CONVENTIONAL RADIOGRAPHY, RADIONUCLIDE IMAGING, AND COMPUTED TOMOGRAPHY (CT)
Final Diagnosis Osteomyelitis of the cortex or periosteum Osteomyelitis of the medullary space Cellulitis Septic joint
Radiography
Radionuclide Images
CT1
3
3
3
0
11
4
11
102
3 2
0 2
0 2
0 0
No. of Patients
CASE II: An 11-year-old boy (D.C.) had a 12-hour history of left foot and ankle pain and fever of 40°C. Blood cultures taken on admission
1 Bone destruction or asymmetric medullary density. Findings inconclusive due to movement.
2
503
504
WORK IN PROGRESS
dullary involvement 4.8 cm above the distal tibia (Fig. 2, B). The medullary densities are shown in TABLE II. The patient responded well to antibiotics and osteomyelitis was never seen radiographically. This is an example of early and perhaps less extensive osteomyelitis; nevertheless, CT showed increased medullary density at an apparently early stage. In large bones such as the tibia, CT may be as sensitive as the radionuclide image in the detection of early osteomyelitis, although our experience is still very limited.
GC
L
A
Fig. 1. CASE I. A. Radionuc/ide scan shows a marked increase in radioactivity in the distal right femoral shaft. Also note the increased radioactivity in the proximal tibial metaphyseal region. Similar findings were seen in the right ankle. B. Transfemoral CT image 13 cm proximal to the distal femoral metaphysis. Swelling of the right leg is presumably due to edema. The right medullary canal is denser than the left. Tissue densities were measured at +33 and -78 Hounsfield units on the right and left, respectively.
TABLE II: Right -86 -65 -65 -58 +18
+77 +239 +426
MEDULLARY DENSITIES IN CASE III (HOUNSFIELD UNITS) Left -82 -14 +24 +52 +151 +173 +296 +448
February 1979
Level (cm) 5.6 4.8
4.0 3.2 3.2
2.4
CASE III: A 16-year-old boy (D.B.) had a persistently draining wound following tibial osteotomy. Radiographs showed soft-tissue swelling of the proximal tibia, marked deformity of the tibia and fibula secondary to the previous osteotomies, and considerable bone sclerosis in the region of the healing osteotomy. A bony fragment was noted in the soft tissues (Fig. 3, A). A radionuclide image showed increased uptake in the proximal tibial shaft in the region of the soft-tissue swelling (Fig. 3, B). Some of this increase in radioactivity was probably related to overlying soft-tissue abnormality, but there was also bony involvement. CT showed intramedullary and cortical sclerosis proximally and soft-tissue swelling anterior to the proximal tibia. A small fragment of bone was again noted in the soft tissues. At the level of maximal soft-tissue abnormality, the underlying tibia showed normal medullary densities between -50 and -60 H, which were similar to those on the normal opposite side (Fig. 3, C). The radionuclide image also showed increased uptake perhaps partially related to overlying cellulitis. However, there was apparent increased activity in the bone, probably due to osteoblastic activity and post-surgical heating. CT was able to visualize normal intramedullary densities and exclude intramedullary infection. Surgically, a soft-tissue infection was found, with a sinus tract going down to the tibial cortex but not involving the bone. The bony fragment in the soft tissues was a small, sequestered fragment from the earlier surgery.
CASE IV: A 12-year-old boy (C.H.) had a three-week history of fever, as well as left thigh pain of two days' duration. The initial clinical impression was osteomyelitis or possible bone or soft-tissue tumor. Some of the examiners found a palpable mass. Radiographs showed cortical thickening along the femoral shaft but no other abnormality. A radionuclide scan showed increased uptake along the midshaft of the femur, consistent with either osteomyelitis or tumor (Fig. 4, A). CT showed a well-demarcated mass with a density of 31 H, which was lower than the surrounding muscle tissue. Thickened cortical bone was seen, but medullary density was normal. There was a small focal area of high -density in the central portion of the low-density mass (Fig. 4, B). A diagnosis of foreign-body abscess with secondary involvement limited to the cortex was established on the basis of the CT scan. A subsequent xeroradiograph demonstrated a tiny foreign body which corresponded to that seen in the original radiograph. The abscess was drained and the cortical bone curetted. Originally the surgeon had planned to "window" the bone but this much more extensive surgery, requiring prolonged hospitalization. was avoided. In this patient, the radionuclide image was unable to distinguish cortical from medullary involvement and did not detect the soft-tissue abscess, whereas CT depicted the clinical situation accurately.
1.6
o(metaphysis)
eventually grew coagulase-positive Staphylococcus aureus. Initial radiographs showed soft-tissue swelling of the ankle medially and posteriorly but no bony abnormality. A radionuc/ide image showed increased activity in the distal tibial metaphysis, consistent with osteomyelitis (Fig. 2, A). CT showed deep soft-tissue swelling and me-
CASE V: An 11-year-old girl (D.J.) had swelling of the right ankle for five days after being kicked in the leg. Radiographs showed medial soft-tissue swelling of the distal third of the lower leg extending down over the medial malleolus. The bones appeared normal. A radionuclide image showed increased soft-tissue activity in the right lower leg; however, there was no perceptible difference in isotope uptake between the normal and the affected side. CT showed soft-tissue swelling of the tibia both medially and posteriorly. Medullary densities were similar
Work In
505 Progress
WORK IN PROGRESS
Vol. 130
bilaterally (TABLE III). Blood cultures were sterile. The bone and joint space was not aspirated. CT confirmed the diagnosis of cellulitis. Neither cellulitis nor hyperemia in the soft tissues appears to affect the medullary densities. It is important to differentiate osteomyelitis from cellulitis because at our facility the former entails 21 days of intravenous antibiotic therapy.
DISCUSSION CT may have a role to play in the diagnosis of osteomyelitis. Our limited experience suggests that increased marrow density occurs early, even with relatively confined infection. The cause of this density change is not known; it may be due to medullary space edema or vascular congestion. It is also not known how early this change occurs. Radionuclide images reflect increased vascularity (2) and are usually positive early in the course of the disease (3), but there have been recent reports of negative or even "cold" bone images during this period (4-7). We have not yet had the opportunity tq perform CT on such patients. When the radionuclide image is positive. CT can differentiate cortical and/or periosteal involvement from intramedullary involvement. It can also detect cortical or periosteal thickening, but usually this diagnosis is established better by conventional radiography. A radionuclide image gives an indication of the activity of such a lesion but often gives nonspecific localization. with the bone shaft appearing "hot," whereas CT may be more specific because of its ability to detect intramedullary abnormality. CT can visualize soft-tissue anatomy better than any combination of other modalities as well as differentiate between overlying soft-tissue and underlying bony pathology. The radionuclide image can usually distinguish between cellulitis and osteomyelitis (3, 8) but may occasionally mistake increased activity in the soft tissues for underlying bony abnormality. CT may be unreliable in the evaluation of infection if the medullary space is too small to measure, such as in the small bones of the hands and feet. Furthermore. it may be difficult to study the humerus with a slow scanner because of respiratory motion. An additional drawback common to both CT and radionuclide imaging is that the distinction between infection and tumor is not always possible, although the former appears to be somewhat more accurate. The nonspecific nature of the change in medullary densities should be stressed:' In addition to inflammation and tumor, a healing fracture will be associated with increased density. We have found that sickle-cell disease, thalassemia, leukemia. and marrow involvement with neuroblastoma also show increased densities. although in such conditions the abnormality is bilateral and symmetrical.
Fig. 2. CASE II. A. Badlonuclidefrnaqeot the ankles shows increaseduptake in the left distal tibial.metaphysis andalso in the bones of the foot, probably secondary to hyperemia. B. CT section 4.8 em above the tibial metaphysis shows extensive soft-tissue swelling about the left tibia. particularly medially. The medullary canal of the left tibia is denser than the right. Tissue densities were measuredat -65 and -14 Hounsfield units on the right and left, respectively.
TABLE III: Right -99 -87 -116 -112 -113 -117 +142
MEDULLARY DENSITIES IN CASE I (HOUNSFIELD UNITS) Level (em)
Left
-98 -95 -120 -116 -115 -108 +144 Image lost to computer error:
5.6 4.8 4.0 3.2 2.4
1.6 O. (metaphysis) .8
REFERENCES CONCLUSION Preliminary experience suggests that CT may be helpful in the diagnosis of osteomyelitis. When the radionuclide study is positive. CT can exclude or establish medullary space involvement, differentiate between overlying soft-tissue and underlying bony abnormality, and clearly delineate the anatomy of the soft tissues.
1. Waldvogel FA. Medoff G, Swartz MN: Osteomyentis: a review of clinical features. therapeutic considerations and unusual aspects. New Eng J Med 282: 198-206.22 Jan 1970 2. GarnettES, Bowen BM, Coates G, et al: An analysis of factors which influence the local accumulation of bone-seeking radiopharmaceuticals. Invest RadioI10:564-568, Nov-Dec 1975 3. Duszynski DO, Kuhn JP, Afshani E, et al: Early radionuclide diagnosis of acute osteomyelitis. Radiology 117:337-340, Nov 1975
506
WORK IN PROGRESS
Fig. 3. CASE IN. A Lateral radiograph of the Jeft leg shows deformity secondary to a healed osteotomy with considerable sclerosis along the shaft of the tibia. No bone destruction was identified. A small bony fragment noted in the soft tissues anterior to the tibia is not visible here. B. Lateral radionuclide imaqe of the left tibia shows increased activity in the tibla.conslstent with osteomyelitis. C. CT scan through the proximal tibiae at the maximal level of bony abnormality. Note the bony fragment anterior to the soft tissues on the left. Soft-tissue swelling is clearly seen medially. Tissue densities were measured at -54 and -60 Hounsfield units on the right and left, respectively.
4. Garnett ES, Cockshott WP, Jacobs J: Classical acute osteomyelitis with a negative bone scan. Br J Radiol 50:757-760, Oct 1977 5. Teates CD, Williamson BR: 'Hot and cold' bone lesion in acute osteomyelitis. Am J RoentgenoI129:517-518, Sep 1977 6. Handmaker H, Leonards R: The bone scan in inflammatory osseous disease. Semin Nucl Med 6:95-105, Jan 1976 7. Russin LD, Staab EV: Unusual bone-scan findings in acute osteomyelitis: case report. J Nucl Med 17:617-619, Jul 1976
February 1979
Fig. 4. CASE IV. A.· Lateral radtonucltde lmaqe shows a definite area of increased uptake in the midfemoral shaft. B. CT scan through the femoral shaft. No significant difference is seen between the intramedullary canals on the right and left sides. In addition to generalized swelling of the left thigh, a large low-density region can be seen in the vast us medialis. The small dense fragment seen in midregion is a foreign body.
8. Gilday DL, Paul DJ, Paterson J: Diagnosis of osteomyelitis in children by combined blood pool and bone imaging. Radiology 117: 331-335, Nov 1975
1 From the Department of Radiology and Nuclear Medicine, Children's Hospital of Buffalo, 219 Bryant St., Buffalo, N.Y. 14222. Presented at the Sixty-third Scientific Assembly and Annual Meeting of the Radiological Society of North America, Chicago, 111., Nov. 27-Dec. 2, 1977. Received Mar. 15, 1978; accepted and revision requested June 12; revision received Oct. 4. as
WORK IN PROGRESS
Computed Tomographic Diagnosis of Osteomyelitis1
Criteria for the final diagnosis included appropriate clinical history and physical findings, positive blood culture or positive bone aspirate, and subsequent radiographic changes [1].
Jerald P. Kuhn, M.D., and Paul E. Berger,JVI.D. Computed tomography (CT) was performed in conjunction with conventional radiography and radionuclide imaging in 22 children with known or suspected osteomyelitis. Preliminary findings suggest that when radionuclide scans are positive, CT can exclude or establish medullary involvement, differentiate between overlying soft-tissue and underlying bony abnormality, and clearly delineate the anatomy of the soft tissues.
RESULTS Eight patients were found to have primary hematogenous osteomyelitis with medullary involvement; 2 had secondary osteomyelitis with medullary involvement; 3 had secondary osteomyelitis limited to the periosteum or the cortex; 3 had cellulitis; 3 had arthritis or synovitis; and 1 had an osteoid osteoma. Two patients had nondiagnostic scans, 1 because the marrow space was too small to measure and the other because of excessive motion. Soft-tissue anatomy in the extremities of young children can be clearly defined by CT, despite the relative lack of body fat. The cortical and periosteal portions of the bone are generally not as well seen as with conventional radiography, but visibility of the medullary cavity is superior. Tissue densities can be measured in the medullary cavity and are similar for both extremities. In the normal child, these densities tend to be in the negative range and may go as low as -120 Hounsfield units. As the ends of the bones are approached, the density increases in proportion to the amount of cancellous bone. Care must be taken to position the extremities symmetrically so that cuts are not taken of cancellous bone on one side and fatty marrow on the other.
Bones, inflammation. Bones, radionuclide studies, 4[0].1299 • Computed tomography, bone, 4 [0] .1211 • (Skeletal system, osteomyelitis, 4 [0] .210) INDEX TERMS:
Radiology 130:503-506, February 1979
Preliminary findings in children with known or suspected osteomyelitis suggest that computed tomography (CT) can be helpful in the diagnosis of this serious and potentially crippling childhood disease. METHODS AND MATERIALS Twenty-two children ranging in age from 4 months to 16 years had serial radiographs of the affected bones (TABLE I). CT was performed using an Ohio Nuclear Model 50 Delta Scanner with an 8-mm collimator and a scanning time of 2:20 to produce two slices. Patients were examined supine with an elastic bandage around the legs for immobilization. Sedation was used in younger, uncooperative children. Both legs or both arms were scanned simultaneously, with the uninvolved extremity used for comparison. Continuous scans were made of the affected area, while one or two cuts were taken of portions of bone away from the area of involvement. Scanning of humeral lesions was difficult due to respiratory motion. Two patients had nondiagnostic scans, one because of excessive motion and the other because the marrow space was too small to measure. The medullary canals in the small bones of the hands and feet were not as clearly defined as in the larger bones. In some patients, the image had to be magnified to obtain relative density measurements; in one, measurements could not be obtained even with magnification. Radionuclide images were made with a gamma camera in all patients in both early and late stages using 99mTc-pyrophosphate in a dose of 400 p,Ci/kg. Radionuclide scans were obtained on a conventional rectilinear scanner.
CASE REPORTS We present several cases showing the types of abnormal findings and the role CT can play in detecting them. CASE I: A14-year-old boy (G.C.) was seen following five days of fever and right thigh and leg pain. Radiographs of the distal femur were normal but there was a progression to characteristic findings of osteomyelitis. A radionuclide scan on admission showed increased uptake in the distal femoral shaft as well as in the epiphyseal portions of the femur, tibia, and fibula (Fig. 1, A). There was also increased radioactivity in the bones of the right ankle. Both the clinical and the radionuclide findings were consistent with osteomyelitis of the distal femur; the changes in the ankle were thought to be related to hyperemia, but a second focus of infection could not be excluded on the basis of the radionuclide scan alone. CT was performed starting 13 cm above the femoral condyle. Even there, a marked difference could be seen between the medullary densities, with the affected extremity having a greater density than the normal side (Fig. 1, B). This differential persisted as the distal femur was approached, until the cancellous bone of the metaphysis was reached, at which time the densities evened out. No abnormality was seen in the distal tibia. In this patient, CT was able to diagnose extensive medullary abnormality at a stage when the radiograph was normal. The radionuclide image was consistent with osteomyelitis of the femur but also suggested abnormality in the distal tibia. CT confirmed the intramedullary abnormality in the femur but showed no evidence of disease in the tibia. SUbsequent clinical events showed no evidence of disease in the ankle.
TABLE I: FINAL DIAGNOSIS AND POSITIVE FINDINGS BY CONVENTIONAL RADIOGRAPHY, RADIONUCLIDE IMAGING, AND COMPUTED TOMOGRAPHY (CT)
Final Diagnosis Osteomyelitis of the cortex or periosteum Osteomyelitis of the medullary space Cellulitis Septic joint
Radiography
Radionuclide Images
CT1
3
3
3
0
11
4
11
102
3 2
0 2
0 2
0 0
No. of Patients
CASE II: An 11-year-old boy (D.C.) had a 12-hour history of left foot and ankle pain and fever of 40°C. Blood cultures taken on admission
1 Bone destruction or asymmetric medullary density. Findings inconclusive due to movement.
2
503
504
WORK IN PROGRESS
dullary involvement 4.8 cm above the distal tibia (Fig. 2, B). The medullary densities are shown in TABLE II. The patient responded well to antibiotics and osteomyelitis was never seen radiographically. This is an example of early and perhaps less extensive osteomyelitis; nevertheless, CT showed increased medullary density at an apparently early stage. In large bones such as the tibia, CT may be as sensitive as the radionuclide image in the detection of early osteomyelitis, although our experience is still very limited.
GC
L
A
Fig. 1. CASE I. A. Radionuc/ide scan shows a marked increase in radioactivity in the distal right femoral shaft. Also note the increased radioactivity in the proximal tibial metaphyseal region. Similar findings were seen in the right ankle. B. Transfemoral CT image 13 cm proximal to the distal femoral metaphysis. Swelling of the right leg is presumably due to edema. The right medullary canal is denser than the left. Tissue densities were measured at +33 and -78 Hounsfield units on the right and left, respectively.
TABLE II: Right -86 -65 -65 -58 +18
+77 +239 +426
MEDULLARY DENSITIES IN CASE III (HOUNSFIELD UNITS) Left -82 -14 +24 +52 +151 +173 +296 +448
February 1979
Level (cm) 5.6 4.8
4.0 3.2 3.2
2.4
CASE III: A 16-year-old boy (D.B.) had a persistently draining wound following tibial osteotomy. Radiographs showed soft-tissue swelling of the proximal tibia, marked deformity of the tibia and fibula secondary to the previous osteotomies, and considerable bone sclerosis in the region of the healing osteotomy. A bony fragment was noted in the soft tissues (Fig. 3, A). A radionuclide image showed increased uptake in the proximal tibial shaft in the region of the soft-tissue swelling (Fig. 3, B). Some of this increase in radioactivity was probably related to overlying soft-tissue abnormality, but there was also bony involvement. CT showed intramedullary and cortical sclerosis proximally and soft-tissue swelling anterior to the proximal tibia. A small fragment of bone was again noted in the soft tissues. At the level of maximal soft-tissue abnormality, the underlying tibia showed normal medullary densities between -50 and -60 H, which were similar to those on the normal opposite side (Fig. 3, C). The radionuclide image also showed increased uptake perhaps partially related to overlying cellulitis. However, there was apparent increased activity in the bone, probably due to osteoblastic activity and post-surgical heating. CT was able to visualize normal intramedullary densities and exclude intramedullary infection. Surgically, a soft-tissue infection was found, with a sinus tract going down to the tibial cortex but not involving the bone. The bony fragment in the soft tissues was a small, sequestered fragment from the earlier surgery.
CASE IV: A 12-year-old boy (C.H.) had a three-week history of fever, as well as left thigh pain of two days' duration. The initial clinical impression was osteomyelitis or possible bone or soft-tissue tumor. Some of the examiners found a palpable mass. Radiographs showed cortical thickening along the femoral shaft but no other abnormality. A radionuclide scan showed increased uptake along the midshaft of the femur, consistent with either osteomyelitis or tumor (Fig. 4, A). CT showed a well-demarcated mass with a density of 31 H, which was lower than the surrounding muscle tissue. Thickened cortical bone was seen, but medullary density was normal. There was a small focal area of high -density in the central portion of the low-density mass (Fig. 4, B). A diagnosis of foreign-body abscess with secondary involvement limited to the cortex was established on the basis of the CT scan. A subsequent xeroradiograph demonstrated a tiny foreign body which corresponded to that seen in the original radiograph. The abscess was drained and the cortical bone curetted. Originally the surgeon had planned to "window" the bone but this much more extensive surgery, requiring prolonged hospitalization. was avoided. In this patient, the radionuclide image was unable to distinguish cortical from medullary involvement and did not detect the soft-tissue abscess, whereas CT depicted the clinical situation accurately.
1.6
o(metaphysis)
eventually grew coagulase-positive Staphylococcus aureus. Initial radiographs showed soft-tissue swelling of the ankle medially and posteriorly but no bony abnormality. A radionuc/ide image showed increased activity in the distal tibial metaphysis, consistent with osteomyelitis (Fig. 2, A). CT showed deep soft-tissue swelling and me-
CASE V: An 11-year-old girl (D.J.) had swelling of the right ankle for five days after being kicked in the leg. Radiographs showed medial soft-tissue swelling of the distal third of the lower leg extending down over the medial malleolus. The bones appeared normal. A radionuclide image showed increased soft-tissue activity in the right lower leg; however, there was no perceptible difference in isotope uptake between the normal and the affected side. CT showed soft-tissue swelling of the tibia both medially and posteriorly. Medullary densities were similar
Work In
505 Progress
WORK IN PROGRESS
Vol. 130
bilaterally (TABLE III). Blood cultures were sterile. The bone and joint space was not aspirated. CT confirmed the diagnosis of cellulitis. Neither cellulitis nor hyperemia in the soft tissues appears to affect the medullary densities. It is important to differentiate osteomyelitis from cellulitis because at our facility the former entails 21 days of intravenous antibiotic therapy.
DISCUSSION CT may have a role to play in the diagnosis of osteomyelitis. Our limited experience suggests that increased marrow density occurs early, even with relatively confined infection. The cause of this density change is not known; it may be due to medullary space edema or vascular congestion. It is also not known how early this change occurs. Radionuclide images reflect increased vascularity (2) and are usually positive early in the course of the disease (3), but there have been recent reports of negative or even "cold" bone images during this period (4-7). We have not yet had the opportunity tq perform CT on such patients. When the radionuclide image is positive. CT can differentiate cortical and/or periosteal involvement from intramedullary involvement. It can also detect cortical or periosteal thickening, but usually this diagnosis is established better by conventional radiography. A radionuclide image gives an indication of the activity of such a lesion but often gives nonspecific localization. with the bone shaft appearing "hot," whereas CT may be more specific because of its ability to detect intramedullary abnormality. CT can visualize soft-tissue anatomy better than any combination of other modalities as well as differentiate between overlying soft-tissue and underlying bony pathology. The radionuclide image can usually distinguish between cellulitis and osteomyelitis (3, 8) but may occasionally mistake increased activity in the soft tissues for underlying bony abnormality. CT may be unreliable in the evaluation of infection if the medullary space is too small to measure, such as in the small bones of the hands and feet. Furthermore. it may be difficult to study the humerus with a slow scanner because of respiratory motion. An additional drawback common to both CT and radionuclide imaging is that the distinction between infection and tumor is not always possible, although the former appears to be somewhat more accurate. The nonspecific nature of the change in medullary densities should be stressed:' In addition to inflammation and tumor, a healing fracture will be associated with increased density. We have found that sickle-cell disease, thalassemia, leukemia. and marrow involvement with neuroblastoma also show increased densities. although in such conditions the abnormality is bilateral and symmetrical.
Fig. 2. CASE II. A. Badlonuclidefrnaqeot the ankles shows increaseduptake in the left distal tibial.metaphysis andalso in the bones of the foot, probably secondary to hyperemia. B. CT section 4.8 em above the tibial metaphysis shows extensive soft-tissue swelling about the left tibia. particularly medially. The medullary canal of the left tibia is denser than the right. Tissue densities were measuredat -65 and -14 Hounsfield units on the right and left, respectively.
TABLE III: Right -99 -87 -116 -112 -113 -117 +142
MEDULLARY DENSITIES IN CASE I (HOUNSFIELD UNITS) Level (em)
Left
-98 -95 -120 -116 -115 -108 +144 Image lost to computer error:
5.6 4.8 4.0 3.2 2.4
1.6 O. (metaphysis) .8
REFERENCES CONCLUSION Preliminary experience suggests that CT may be helpful in the diagnosis of osteomyelitis. When the radionuclide study is positive. CT can exclude or establish medullary space involvement, differentiate between overlying soft-tissue and underlying bony abnormality, and clearly delineate the anatomy of the soft tissues.
1. Waldvogel FA. Medoff G, Swartz MN: Osteomyentis: a review of clinical features. therapeutic considerations and unusual aspects. New Eng J Med 282: 198-206.22 Jan 1970 2. GarnettES, Bowen BM, Coates G, et al: An analysis of factors which influence the local accumulation of bone-seeking radiopharmaceuticals. Invest RadioI10:564-568, Nov-Dec 1975 3. Duszynski DO, Kuhn JP, Afshani E, et al: Early radionuclide diagnosis of acute osteomyelitis. Radiology 117:337-340, Nov 1975
506
WORK IN PROGRESS
Fig. 3. CASE IN. A Lateral radiograph of the Jeft leg shows deformity secondary to a healed osteotomy with considerable sclerosis along the shaft of the tibia. No bone destruction was identified. A small bony fragment noted in the soft tissues anterior to the tibia is not visible here. B. Lateral radionuclide imaqe of the left tibia shows increased activity in the tibla.conslstent with osteomyelitis. C. CT scan through the proximal tibiae at the maximal level of bony abnormality. Note the bony fragment anterior to the soft tissues on the left. Soft-tissue swelling is clearly seen medially. Tissue densities were measured at -54 and -60 Hounsfield units on the right and left, respectively.
4. Garnett ES, Cockshott WP, Jacobs J: Classical acute osteomyelitis with a negative bone scan. Br J Radiol 50:757-760, Oct 1977 5. Teates CD, Williamson BR: 'Hot and cold' bone lesion in acute osteomyelitis. Am J RoentgenoI129:517-518, Sep 1977 6. Handmaker H, Leonards R: The bone scan in inflammatory osseous disease. Semin Nucl Med 6:95-105, Jan 1976 7. Russin LD, Staab EV: Unusual bone-scan findings in acute osteomyelitis: case report. J Nucl Med 17:617-619, Jul 1976
February 1979
Fig. 4. CASE IV. A.· Lateral radtonucltde lmaqe shows a definite area of increased uptake in the midfemoral shaft. B. CT scan through the femoral shaft. No significant difference is seen between the intramedullary canals on the right and left sides. In addition to generalized swelling of the left thigh, a large low-density region can be seen in the vast us medialis. The small dense fragment seen in midregion is a foreign body.
8. Gilday DL, Paul DJ, Paterson J: Diagnosis of osteomyelitis in children by combined blood pool and bone imaging. Radiology 117: 331-335, Nov 1975
1 From the Department of Radiology and Nuclear Medicine, Children's Hospital of Buffalo, 219 Bryant St., Buffalo, N.Y. 14222. Presented at the Sixty-third Scientific Assembly and Annual Meeting of the Radiological Society of North America, Chicago, 111., Nov. 27-Dec. 2, 1977. Received Mar. 15, 1978; accepted and revision requested June 12; revision received Oct. 4. as
