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Pyomyositis: Early detection utilizing multiple imaging modalities
Magnetic Resonance Printed in the USA.
l
Imaging, Vol. 9. pp. 187-193, All rights reserved.
1991 Copyright
0730-725x/91 $3.00 + .oo 0 1991 Pergamon Press plc
Original Contribution PYOMYOSITIS: EARLY DETECTION UTILIZING MULTIPLE IMAGING MODALITIES GREGORY R. APPLEGATE* AND ALLEN J. COHEN-f*Department of Diagnostic Radiology and the Pittsburgh NMR Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, TDepartment of Radiological Sciences, University of California-Irvine, Irvine, California 92668, USA Pyomyositis represents 3% to 4% of surgical admissions in East Africa, however, there were no reported cases in the United States prior to 1971. Since, there have been numerous reports of this entity. Four recent cases are presented utilizing multiple imaging modalities including magnetic resonance. MR was very sensitive to early soft tissue inflammatory processes and demonstrated these focal abscesses with superior anatomic localization. MR is advocated in the initial evaluation of a focal process. In a systemic, nonfocal process, nuclear medicine WBC or Gallium Scans to localize areas for further MR scanning is recommended. Keywords: Musculoskeletal;
Magnetic resonance imaging; Abscesses;
Pyomyositis is a disease characterized by single or multiple skeletal muscle abscesses most often involving the gluteal region and thigh.’ In 83% to 98% of reported cases, Staphylococcus aureus is the responsible organism. ‘9’ Closed trauma producing damaged muscle with subsequent seeding from a source of pyogenie bacteria has been implicated as an etiological factor, although direct muscle trauma has been reported in only 22% to 61% of reported cases.‘s3*4 Forty percent of patients do have multiple abscesses and a bacteremic state would seem plausible, although less than 5% to 29% of patients have positive blood cultures during their illness. ‘,3 The disease has a predilection for children, and a second group 25 to 45 years of age, with males more frequently involved than females.‘s3 It presents as a subacute illness with ill-defined muscle pain which precedes fever by days to weeks. The pain, swelling, and erythema may not be striking and is often described as “hard, ” “woody,” or “elastic” involving solitary or multiple sites of up to six muscle groups.‘y5
RECEIVED
6/21/90;
ACCEPTED
Nuclear medicine.
The quadriceps and trunk muscles are frequently affected as well as the right iliac fossa. The latter location has been clinically misdiagnosed as appendicitis in previous reports. Laboratory data may not be helpful, as patients may present with a normal white count and with normal muscle enzymes, CPK and LDH. Elevated sedimentation rate and eosinophilia have been reported.’ The diagnosis is often made with needle biopsy. Treatment is usually with incision and drainage or ultrasound-guided percutaneous drainage with antibiotic therapy utilizing beta lactamase resistant penicillin. Mortality has been reported to range from 1% to 25%. 1*4The differential diagnosis often includes osteomyelitis, cellulitis, muscle hematoma or tear, thrombophlebitis, or soft tissue neoplasm. While Gallium or Indium scintigraphy has been used to demonstrate sites of soft tissue infection, CT may be necessary to characterize possible false-positive sites of isotope accumulation. A recent report demonstrated two cases of pyomyositis diagnosed with magnetic resonance imaging (MR).6 We report the MR appear-
Address all correspondence to Gregory R. Applegate, MD, Department of Diagnostic Radiology, Pittsburgh NMR Institute, University of Pittsburgh, 3260 Fifth Ave., Pittsburgh, PA 15213, USA.
9/20/90.
authors wish to acknowledge Betty Trent and Kathryn Frazier for assistancein manuscript preparation; also Drs. F. Leland Thaete and Hollis Fritts for providing some of the case materials. Acknowledgments-The
187
188
Magnetic Resonance Imaging 0 Volume 9, Number 2, 1991
ante of four recent cases of pyomyositis evaluated at our institutions and compare the MR appearance to other imaging modalities. Case I A 45year-old male complained of a one-month history of leg pain and swelling. Six weeks prior to admission the patient reported a twisting injury of his left knee, treated elsewhere with a posterior splint. Two weeks later the swelling in his left leg had doubled in size. A venogram revealed deep vein thrombosis of the calf veins. He continued to have persistent pain, tenderness, and swelling, and was admitted three weeks later. His past medical history was significant for gonococcal urethritis treated six weeks prior to admission with an adequate course of penicillin. Physical exam was significant for 3+ pitting edema of his left lower extremity with a firm area reported over his anterior thigh. An Indium-1 11 labeled white blood cell study (In-111 WBC) (Fig. 1) performed because of persistent thigh swelling, revealed a diffuse area of increased activity in the left thigh consistent with soft tissue necrosis and/or abscess. Ultrasonic examination demonstrated multiple fluid collections in the anterior muscles of the thigh. Aspiration obtained a culture negative seropurulent material. Magnetic resonance imaging revealed complete replacement of the normal musculature by multiloculated areas of increased signal intensity on the long TR images which are consis-
Fig. 1. Indium-1 11 labeled white blood cell scan reveals an area of increased activity in the region of the left proximal femur and surrounding soft tissues.
Fig. 2. Coronal proton density-weighted MRI, TR 2500, TE 33 msec, demonstrate multiloculated areas of increased signal intensity throughout muscles of the anterior thigh.
tent with multiple abscesses (Fig. 2). The posterior musculature appeared to be normal. The patient underwent incision and drainage and received intravenous penicillin. A later MR scan demonstrated partial resolution of the loculated fluid collections. Case 2 A 42-year-old male, 7 years status postpancreaticojejunostomy for chronic pancreatitis with insulin-dependent diabetes mellitus was admitted in diabetic ketoacidosis and had two cardiac arrests. He later received intramuscular injections for abdominal pain and subsequently developed a left foot drop felt initially to be due to diabetic neuropathy or toxic metabolic factors. An Indium-labeled white blood cell (WBC) study performed to evaluate for possible colitis as a cause for his abdominal pain and sepsis revealed an area of increased uptake in both proximal femurs as well as colonic uptake consistent with colitis. Plain films of both hips were normal. A later Gallium scan (Fig. 3) revealed areas of increased uptake in both proximal thighs, the left greater than the right, in similar areas to those identified on the Indium WBC. Both thighs were hard and painful to palpation at that time. Magnetic resonance imaging demon-
Pyomyositis 0 G.R.
APPLEGATE AND
A.J.
COHEN
189
Fig. 3. Gallium-67 citrate scan of the anterior pelvis reveals areas of increased uptake in both proximal thigh regions, greater on the left (arrow) than on the right.
strated multiple high-signal intensity areas on the long TR images consistent with bilateral soft tissue abscesses (Fig. 4). Aspiration of fluid from the abscesses
Fig. 4. Coronal MRI, TR 2500 msec, TE 53 msec, reveal bilateral areas of increased signal intensity within the anterior thigh musculature (arrows).
was purulent but culture negative, therefore no surgical incision and drainage was performed. Case 3 A 54-year-old white male with diabetes mellitus complained of a four-week history of gradually worsening bilateral groin pain, right greater than left, after minor trauma. He also reported fever and chills. Physical examination revealed suprapubic and groin tenderness and marked pain on range of motion of the hips. On admission, plain hip and pelvis films were normal. A bone scan with blood pool and delayed images revealed an abnormal focus on the blood pool image in the region of the pubic rami (Fig. 5) noted in retrospect. This area was obscured by the lead bladder shield on delayed images. CT examination revealed enlargement of both inferior rectus muscles, right greater than left, with focal low attenuation inhomogeneity near the right rectus insertion into the pubis. The differential diagnosis offered was early infection vs. hematoma with rhabdomyosarcoma less likely (Fig. 6). Bone windows revealed no bony abnormality. A Gallium SPECT scan performed at 72 hours revealed abnormal Gallium accumulation anteriorly in the pelvis near the pubis, more prominent on the right (Fig. 7). Two ultrasound examinations were performed.
Fig. 5. Blood pool image over the anterior pelvis following intravenous administration of 20 mCi of Technetium-99m MDP reveals abnormal blood pool activity within the midinferior pelvis.
190
Magnetic Resonance Imaging 0 Volume 9, Number 2, 1991
Fig. 6. Axial CT examination demonstrating enlargement of the inferior rectus muscles more prominent on the right with a low attenuation central focus on the right (see arrow).
The initial examination (Fig. 8) revealed an ill-defined hypoechoic diffuse infiltrative pattern of the right rectus muscle which five days later developed a discrete well-defined hypoechoic areas in addition to diffuse enlargement of the inferior aspect. MR revealed swelling of the rectus abdominis muscles, right much
greater than left, extending from the umbilicus to pubis. Areas in the inferior aspect of the right rectus are low signal intensity on short TR images (Fig. 9) and high signal on long TR images (Fig. 10) consistent with fluid, pus and/or edema but unlikely to be evolving hematoma. There is also an abnormal focus of low signal intensity on short TR images and high signal intensity on long TR images replacing the normal marrow of the right pubic bone representing osseous extension of the inflammatory process. Blood cultures drawn on admission were positive for group A betahemolytic streptococcus. Repeat MRI examination approximately three weeks following antibiotic therapy revealed overall improvement with diminished size and degree of signal intensity changes in the inferior aspect of the right rectus muscle. Case 4 A 49-year-old male reported severe swelling and inability to extend the left knee for approximately one month. The left lower extremity was discolored below the knee with a purple mottled appearance. A CT examination (Fig. 11) revealed soft tissue swelling with diffuse edema anterior to the distal left femur. There is a crescent-shaped area of low attenuation centrally within this soft tissue swelling which was felt to rep-
Fig. 7. Gallium-67 citrate SPECT examination at 72 hours, reconstructions displayed in the coronal plane (images are displayed posterior left top to anterior right bottom). Abnormal Gallium accumulation anteriorly in the pelvis near the pubis is more prominent on the right (arrows).
Pyomyositis 0 G.R.
Fig. 8. Transverse ultrasound
examination
APPLEGATE AND A.J. COHEN
191
obtained in the right lower quadrant just to the right of midline reveals a large
central hypoechoic area within the rectus abdominus muscle.
resent an area of necrosis. Aspiration of this area revealed multiple white cells yet was culture negative. Aspiration nine days later revealed aerobic diptheroids with few white cells. Blood cultures were all negative. Sagittal short TR images (Fig. 12) revealed diffuse swelling anterior to the distal left femur with a discrete
Fig. 9. Axial MRI with TR 400 msec, TE 20 msec, with low signal intensity enlargement of the right rectus abdominus (arrow).
3 cm area of intermediate signal intensity. On long TR images (Fig. 13) in the axial plane this area is higher signal intensity consistent with a complex fluid collection. Case 5 An 1l-year-old black male with a 15day history of left thigh pain, swelling and inability to bear weight. Upon admission patient was toxic appearing with tachycardia and hypotension. The left thigh was indurated, tender and had a girth of 5 cm larger than the right thigh. White blood cell count was 7.9 with 51% bands upon admission. Creatine phosphokinase (CPK) was elevated at 1932 as was the ethrothocyte sedimentation rate (ESR) at 71. Blood, throat, and muscle biopsy cultures all were positive for group A streptococcus and the patient was started on a course of intravenous ampicillin. Plain film evaluation of the left hip and femur were negative. MRI examination revealed multiloculated areas of increased signal intensity on the long TR images involving the adductor magnus extending into the pelvis to involve the obturator internus with displacement of the bladder to the right (Fig. 14). On short TR/TE sequences there was abnormal swelling of the medial thigh compartment and vague areas of signal inhomogeneity identified. Following gadolinium administration the abnormal areas seen on the long TR images demonstrated contrast enhancement.
Magnetic Resonance Imaging 0 Volume 9, Number 2, 1991
192
Fig. 10. Coronal MRI with TR 3500 msec, TE 40 msec. Abnormal area of high signal intensity within the right rectus abdominus muscle near its insertion into the pubic ramus (arrow).
Fig. 12. Sagittal MRI with TR 600 msec, TE 20 msec, reveals an intermediate signal intensity focus just anterior to the distal femur with overlying soft tissue swelling (arrow). (Note: Leg positioned in extreme external rotation due to patient’s inability to extend the left knee.)
CONCLUSION
United States, its prompt diagnosis can lead to effective clinical management. Magnetic resonance imaging is very sensitive in detecting subtle soft tissue inflammatory processes. Signal characteristics may help to
differentiate evolving hematomas from simple and many complex fluid collections. MR is also sensitive for the early changes of osteomyelitis combined with the ability to demonstrate these focal abscesses with superior anatomic localization.’ In addition MR can determine if there is a focal
Fig. 11. Axial contrast enhanced CT examination through the distal femurs reveals diffuse swelling of the left anterior thigh with a central area of low attenuation (arrow).
Fig. 13. Axial MRI with TR 3000 msec, TE 80 msec. There is an area of abnormally increased signal intensity (arrow) corresponding with intermediate signal intensity area seen on the short TR images (Fig. 12).
Although
pyomyositis
is a rare clinical entity in the
Pyomyositis 0 G.R.
APPLEGATE
AND
A.J.
COHEN
193
loculated process amenable to percutaneous drainage or a more diffuse process that may require open surgical drainage. Therefore MR can readily help guide clinical management of this disease process. If there is a clinical suspicion as to the presence of focal pyomyositis, we advocate initial evaluation with magnetic resonance imaging. If there is a question of remote sites of pyomyositis, nuclear medicine wholebody WBC or Gallium scans help to localize areas for further MR scanning. REFERENCES
Fig. 14. Coronal MRI with TR 2500 msec, TE 80 msec, reveals multiple areas of increased signal intensity within the adductor magnus (arrow) extending into the pelvis, involving the obturator internus (arrowhead) with displacement of the bladder to the right.
1. Chiedozi, L.C. Pyomyositis. .I. Surg. 137:255; 1979. 2. Yousefzadeh, D.K.; Schumann, E.M.; Mulligan, G.M.; Bosworth, D.E.; Young, C.S.; Pringle, K.C. The role of imaging modalities in diagnosis and management of pyomyositis. Skeletal Radiol. 8:285; 1982. 3. Brown, J.D.; Wheeler, B. Pyomyositis: Report of 18 cases in Hawaii. Arch. Intern Med. 144:1749; 1984. 4. Minor, R.L.; Baum, S.; Schulze-Delrieu, K.S. Pyomyositis in a patient with progressive systemic sclerosis. Arch. Intern Med. 148:1453; 1988. 5. Datz, F.L.; Lewis, S.E.; Conrad, M.R.; Maravilla, A.; Parkey, R.W. Pyomyositis diagnosed by radionuclide imaging and ultrasonography. South. Med. J. 73~649; 1980. 6. Yuh, W.T.C.; Schreiber, A.E.; Montgomery, W.J.; Ehara, S. Magnetic resonance imaging of pyomyositis. Skeletal Radiol. 17:190-193; 1988. 7. Medic, M.T.; Planze, W.; Feiglin, D.H.I.; Belhobek, G. Magnetic resonance imaging of musculoskeletal infections. Radiol. Clin. North Am. 24~247; 1986.
l
Imaging, Vol. 9. pp. 187-193, All rights reserved.
1991 Copyright
0730-725x/91 $3.00 + .oo 0 1991 Pergamon Press plc
Original Contribution PYOMYOSITIS: EARLY DETECTION UTILIZING MULTIPLE IMAGING MODALITIES GREGORY R. APPLEGATE* AND ALLEN J. COHEN-f*Department of Diagnostic Radiology and the Pittsburgh NMR Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, TDepartment of Radiological Sciences, University of California-Irvine, Irvine, California 92668, USA Pyomyositis represents 3% to 4% of surgical admissions in East Africa, however, there were no reported cases in the United States prior to 1971. Since, there have been numerous reports of this entity. Four recent cases are presented utilizing multiple imaging modalities including magnetic resonance. MR was very sensitive to early soft tissue inflammatory processes and demonstrated these focal abscesses with superior anatomic localization. MR is advocated in the initial evaluation of a focal process. In a systemic, nonfocal process, nuclear medicine WBC or Gallium Scans to localize areas for further MR scanning is recommended. Keywords: Musculoskeletal;
Magnetic resonance imaging; Abscesses;
Pyomyositis is a disease characterized by single or multiple skeletal muscle abscesses most often involving the gluteal region and thigh.’ In 83% to 98% of reported cases, Staphylococcus aureus is the responsible organism. ‘9’ Closed trauma producing damaged muscle with subsequent seeding from a source of pyogenie bacteria has been implicated as an etiological factor, although direct muscle trauma has been reported in only 22% to 61% of reported cases.‘s3*4 Forty percent of patients do have multiple abscesses and a bacteremic state would seem plausible, although less than 5% to 29% of patients have positive blood cultures during their illness. ‘,3 The disease has a predilection for children, and a second group 25 to 45 years of age, with males more frequently involved than females.‘s3 It presents as a subacute illness with ill-defined muscle pain which precedes fever by days to weeks. The pain, swelling, and erythema may not be striking and is often described as “hard, ” “woody,” or “elastic” involving solitary or multiple sites of up to six muscle groups.‘y5
RECEIVED
6/21/90;
ACCEPTED
Nuclear medicine.
The quadriceps and trunk muscles are frequently affected as well as the right iliac fossa. The latter location has been clinically misdiagnosed as appendicitis in previous reports. Laboratory data may not be helpful, as patients may present with a normal white count and with normal muscle enzymes, CPK and LDH. Elevated sedimentation rate and eosinophilia have been reported.’ The diagnosis is often made with needle biopsy. Treatment is usually with incision and drainage or ultrasound-guided percutaneous drainage with antibiotic therapy utilizing beta lactamase resistant penicillin. Mortality has been reported to range from 1% to 25%. 1*4The differential diagnosis often includes osteomyelitis, cellulitis, muscle hematoma or tear, thrombophlebitis, or soft tissue neoplasm. While Gallium or Indium scintigraphy has been used to demonstrate sites of soft tissue infection, CT may be necessary to characterize possible false-positive sites of isotope accumulation. A recent report demonstrated two cases of pyomyositis diagnosed with magnetic resonance imaging (MR).6 We report the MR appear-
Address all correspondence to Gregory R. Applegate, MD, Department of Diagnostic Radiology, Pittsburgh NMR Institute, University of Pittsburgh, 3260 Fifth Ave., Pittsburgh, PA 15213, USA.
9/20/90.
authors wish to acknowledge Betty Trent and Kathryn Frazier for assistancein manuscript preparation; also Drs. F. Leland Thaete and Hollis Fritts for providing some of the case materials. Acknowledgments-The
187
188
Magnetic Resonance Imaging 0 Volume 9, Number 2, 1991
ante of four recent cases of pyomyositis evaluated at our institutions and compare the MR appearance to other imaging modalities. Case I A 45year-old male complained of a one-month history of leg pain and swelling. Six weeks prior to admission the patient reported a twisting injury of his left knee, treated elsewhere with a posterior splint. Two weeks later the swelling in his left leg had doubled in size. A venogram revealed deep vein thrombosis of the calf veins. He continued to have persistent pain, tenderness, and swelling, and was admitted three weeks later. His past medical history was significant for gonococcal urethritis treated six weeks prior to admission with an adequate course of penicillin. Physical exam was significant for 3+ pitting edema of his left lower extremity with a firm area reported over his anterior thigh. An Indium-1 11 labeled white blood cell study (In-111 WBC) (Fig. 1) performed because of persistent thigh swelling, revealed a diffuse area of increased activity in the left thigh consistent with soft tissue necrosis and/or abscess. Ultrasonic examination demonstrated multiple fluid collections in the anterior muscles of the thigh. Aspiration obtained a culture negative seropurulent material. Magnetic resonance imaging revealed complete replacement of the normal musculature by multiloculated areas of increased signal intensity on the long TR images which are consis-
Fig. 1. Indium-1 11 labeled white blood cell scan reveals an area of increased activity in the region of the left proximal femur and surrounding soft tissues.
Fig. 2. Coronal proton density-weighted MRI, TR 2500, TE 33 msec, demonstrate multiloculated areas of increased signal intensity throughout muscles of the anterior thigh.
tent with multiple abscesses (Fig. 2). The posterior musculature appeared to be normal. The patient underwent incision and drainage and received intravenous penicillin. A later MR scan demonstrated partial resolution of the loculated fluid collections. Case 2 A 42-year-old male, 7 years status postpancreaticojejunostomy for chronic pancreatitis with insulin-dependent diabetes mellitus was admitted in diabetic ketoacidosis and had two cardiac arrests. He later received intramuscular injections for abdominal pain and subsequently developed a left foot drop felt initially to be due to diabetic neuropathy or toxic metabolic factors. An Indium-labeled white blood cell (WBC) study performed to evaluate for possible colitis as a cause for his abdominal pain and sepsis revealed an area of increased uptake in both proximal femurs as well as colonic uptake consistent with colitis. Plain films of both hips were normal. A later Gallium scan (Fig. 3) revealed areas of increased uptake in both proximal thighs, the left greater than the right, in similar areas to those identified on the Indium WBC. Both thighs were hard and painful to palpation at that time. Magnetic resonance imaging demon-
Pyomyositis 0 G.R.
APPLEGATE AND
A.J.
COHEN
189
Fig. 3. Gallium-67 citrate scan of the anterior pelvis reveals areas of increased uptake in both proximal thigh regions, greater on the left (arrow) than on the right.
strated multiple high-signal intensity areas on the long TR images consistent with bilateral soft tissue abscesses (Fig. 4). Aspiration of fluid from the abscesses
Fig. 4. Coronal MRI, TR 2500 msec, TE 53 msec, reveal bilateral areas of increased signal intensity within the anterior thigh musculature (arrows).
was purulent but culture negative, therefore no surgical incision and drainage was performed. Case 3 A 54-year-old white male with diabetes mellitus complained of a four-week history of gradually worsening bilateral groin pain, right greater than left, after minor trauma. He also reported fever and chills. Physical examination revealed suprapubic and groin tenderness and marked pain on range of motion of the hips. On admission, plain hip and pelvis films were normal. A bone scan with blood pool and delayed images revealed an abnormal focus on the blood pool image in the region of the pubic rami (Fig. 5) noted in retrospect. This area was obscured by the lead bladder shield on delayed images. CT examination revealed enlargement of both inferior rectus muscles, right greater than left, with focal low attenuation inhomogeneity near the right rectus insertion into the pubis. The differential diagnosis offered was early infection vs. hematoma with rhabdomyosarcoma less likely (Fig. 6). Bone windows revealed no bony abnormality. A Gallium SPECT scan performed at 72 hours revealed abnormal Gallium accumulation anteriorly in the pelvis near the pubis, more prominent on the right (Fig. 7). Two ultrasound examinations were performed.
Fig. 5. Blood pool image over the anterior pelvis following intravenous administration of 20 mCi of Technetium-99m MDP reveals abnormal blood pool activity within the midinferior pelvis.
190
Magnetic Resonance Imaging 0 Volume 9, Number 2, 1991
Fig. 6. Axial CT examination demonstrating enlargement of the inferior rectus muscles more prominent on the right with a low attenuation central focus on the right (see arrow).
The initial examination (Fig. 8) revealed an ill-defined hypoechoic diffuse infiltrative pattern of the right rectus muscle which five days later developed a discrete well-defined hypoechoic areas in addition to diffuse enlargement of the inferior aspect. MR revealed swelling of the rectus abdominis muscles, right much
greater than left, extending from the umbilicus to pubis. Areas in the inferior aspect of the right rectus are low signal intensity on short TR images (Fig. 9) and high signal on long TR images (Fig. 10) consistent with fluid, pus and/or edema but unlikely to be evolving hematoma. There is also an abnormal focus of low signal intensity on short TR images and high signal intensity on long TR images replacing the normal marrow of the right pubic bone representing osseous extension of the inflammatory process. Blood cultures drawn on admission were positive for group A betahemolytic streptococcus. Repeat MRI examination approximately three weeks following antibiotic therapy revealed overall improvement with diminished size and degree of signal intensity changes in the inferior aspect of the right rectus muscle. Case 4 A 49-year-old male reported severe swelling and inability to extend the left knee for approximately one month. The left lower extremity was discolored below the knee with a purple mottled appearance. A CT examination (Fig. 11) revealed soft tissue swelling with diffuse edema anterior to the distal left femur. There is a crescent-shaped area of low attenuation centrally within this soft tissue swelling which was felt to rep-
Fig. 7. Gallium-67 citrate SPECT examination at 72 hours, reconstructions displayed in the coronal plane (images are displayed posterior left top to anterior right bottom). Abnormal Gallium accumulation anteriorly in the pelvis near the pubis is more prominent on the right (arrows).
Pyomyositis 0 G.R.
Fig. 8. Transverse ultrasound
examination
APPLEGATE AND A.J. COHEN
191
obtained in the right lower quadrant just to the right of midline reveals a large
central hypoechoic area within the rectus abdominus muscle.
resent an area of necrosis. Aspiration of this area revealed multiple white cells yet was culture negative. Aspiration nine days later revealed aerobic diptheroids with few white cells. Blood cultures were all negative. Sagittal short TR images (Fig. 12) revealed diffuse swelling anterior to the distal left femur with a discrete
Fig. 9. Axial MRI with TR 400 msec, TE 20 msec, with low signal intensity enlargement of the right rectus abdominus (arrow).
3 cm area of intermediate signal intensity. On long TR images (Fig. 13) in the axial plane this area is higher signal intensity consistent with a complex fluid collection. Case 5 An 1l-year-old black male with a 15day history of left thigh pain, swelling and inability to bear weight. Upon admission patient was toxic appearing with tachycardia and hypotension. The left thigh was indurated, tender and had a girth of 5 cm larger than the right thigh. White blood cell count was 7.9 with 51% bands upon admission. Creatine phosphokinase (CPK) was elevated at 1932 as was the ethrothocyte sedimentation rate (ESR) at 71. Blood, throat, and muscle biopsy cultures all were positive for group A streptococcus and the patient was started on a course of intravenous ampicillin. Plain film evaluation of the left hip and femur were negative. MRI examination revealed multiloculated areas of increased signal intensity on the long TR images involving the adductor magnus extending into the pelvis to involve the obturator internus with displacement of the bladder to the right (Fig. 14). On short TR/TE sequences there was abnormal swelling of the medial thigh compartment and vague areas of signal inhomogeneity identified. Following gadolinium administration the abnormal areas seen on the long TR images demonstrated contrast enhancement.
Magnetic Resonance Imaging 0 Volume 9, Number 2, 1991
192
Fig. 10. Coronal MRI with TR 3500 msec, TE 40 msec. Abnormal area of high signal intensity within the right rectus abdominus muscle near its insertion into the pubic ramus (arrow).
Fig. 12. Sagittal MRI with TR 600 msec, TE 20 msec, reveals an intermediate signal intensity focus just anterior to the distal femur with overlying soft tissue swelling (arrow). (Note: Leg positioned in extreme external rotation due to patient’s inability to extend the left knee.)
CONCLUSION
United States, its prompt diagnosis can lead to effective clinical management. Magnetic resonance imaging is very sensitive in detecting subtle soft tissue inflammatory processes. Signal characteristics may help to
differentiate evolving hematomas from simple and many complex fluid collections. MR is also sensitive for the early changes of osteomyelitis combined with the ability to demonstrate these focal abscesses with superior anatomic localization.’ In addition MR can determine if there is a focal
Fig. 11. Axial contrast enhanced CT examination through the distal femurs reveals diffuse swelling of the left anterior thigh with a central area of low attenuation (arrow).
Fig. 13. Axial MRI with TR 3000 msec, TE 80 msec. There is an area of abnormally increased signal intensity (arrow) corresponding with intermediate signal intensity area seen on the short TR images (Fig. 12).
Although
pyomyositis
is a rare clinical entity in the
Pyomyositis 0 G.R.
APPLEGATE
AND
A.J.
COHEN
193
loculated process amenable to percutaneous drainage or a more diffuse process that may require open surgical drainage. Therefore MR can readily help guide clinical management of this disease process. If there is a clinical suspicion as to the presence of focal pyomyositis, we advocate initial evaluation with magnetic resonance imaging. If there is a question of remote sites of pyomyositis, nuclear medicine wholebody WBC or Gallium scans help to localize areas for further MR scanning. REFERENCES
Fig. 14. Coronal MRI with TR 2500 msec, TE 80 msec, reveals multiple areas of increased signal intensity within the adductor magnus (arrow) extending into the pelvis, involving the obturator internus (arrowhead) with displacement of the bladder to the right.
1. Chiedozi, L.C. Pyomyositis. .I. Surg. 137:255; 1979. 2. Yousefzadeh, D.K.; Schumann, E.M.; Mulligan, G.M.; Bosworth, D.E.; Young, C.S.; Pringle, K.C. The role of imaging modalities in diagnosis and management of pyomyositis. Skeletal Radiol. 8:285; 1982. 3. Brown, J.D.; Wheeler, B. Pyomyositis: Report of 18 cases in Hawaii. Arch. Intern Med. 144:1749; 1984. 4. Minor, R.L.; Baum, S.; Schulze-Delrieu, K.S. Pyomyositis in a patient with progressive systemic sclerosis. Arch. Intern Med. 148:1453; 1988. 5. Datz, F.L.; Lewis, S.E.; Conrad, M.R.; Maravilla, A.; Parkey, R.W. Pyomyositis diagnosed by radionuclide imaging and ultrasonography. South. Med. J. 73~649; 1980. 6. Yuh, W.T.C.; Schreiber, A.E.; Montgomery, W.J.; Ehara, S. Magnetic resonance imaging of pyomyositis. Skeletal Radiol. 17:190-193; 1988. 7. Medic, M.T.; Planze, W.; Feiglin, D.H.I.; Belhobek, G. Magnetic resonance imaging of musculoskeletal infections. Radiol. Clin. North Am. 24~247; 1986.