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Time-density analysis in the evaluation of CT pseudotumors
Current Cases & Concepts Time-Density Analysis in the Evaluation of CT Pseudotumors Michael A. Noon, M.D.’ Stuart W. Young, M.D.2
scan time) without intravenous contrast agents. At a preselected level through the mass in question, a repeat precontrast control scan was obtained. The patient then received an antecubital intravenous bolus of 50 ml of Renografin-76 (Squibb) followed by scans taken as rapidly as possible (technically limited to approximately every 20 set following the initiation of the bolus). An area of interest was used to measure the Hounsfield CT units and the time-density relationships.
Division of Diagnostic Radiology, Department of Radiology, Stanford University School of Medicine, Stanford, California CT time-density analysis was clinically applied in two case situations in which the etiology of apparent pseudotumors was in question. The enhancement characteristics of these pseudotumors were compared to those of normal tissues, which permitted their correct identification. Time-density analysis was a clinically useful technique in the investigation of unusual CT findings.
CASE REPORTS
Case 1
A most difficult diagnostic task in clinical CT scanning, as in other areas of radiology and medicine, is to distinguish variations of normal from the truly abnormal. With the judicious use of intravenous contrast agents, clinically useful information can be generated by dynamic computed tomography (l-4) and the analysis of the time-density curves (5). These studies demonstrate the clinical usefulness of a time-density analysis of potentially abnormal masses, which were shown by this methodology to be unusual configurations of normal structures. MATERIALS
The patient was a 69-year-old woman admitted for progressive leg weakness and numbness. Thirteen months previously she was diagnosed and treated
AND METHODS
CT scans of the abdomen and pelvis were performed on a GE CT/T 8800 (lo-mm slice thickness, 9.8-set This study was supported in part by grants from the T. F. EckStrom Trust and grants from the NCI, DHEW, CA 24879, and CA 5838. Address correspondence to Stuart W. Young, M.D., Department of Radiology, Stanford University Medical Center, Stanford, California 94305. ‘Present address: Department of Radiology, Scripps Memorial Hospital, 9888 Genesee Avenue, La Jolla, California 92037. ‘Clinical Faculty Fellow, American Cancer Society.
Noon and Young 166
Figure 1. CT scan through the mid-pelvis in a patient with lymphoma and right hip pain. The right-sided pelvic mass (NOW) had been diagnosed on a previous scan in another hospital as recurrent lymphoma.
CT:
the journal of Computed
Tomography,
Copyright
0 University Park Press, 1981 Vol. 5. No. 2, Printed In U.S.A.
with local radiation therapy for a submandibular mass proven by biopsy to represent diffuse histiocytic lymphoma. Other staging procedures, including a lymphangiogram and bone marrow biopsy, were negative. Six months prior to this admission she developed back pain and sweats. In examinations made before she was referred to our institution, a bone scan was
diffusely positive, a bone marrow biopsy was positive for lymphoma, and a CT scan was interpreted as showing a right posterolateral pelvic mass compatible with lymphoma. She was begun on chemotherapy with improvement in her symptomatology. Ten days prior to admission she complained of increasing pain and weakness, especially in her right leg, and required ambuiatory assistance. A myelo-
Figure 2. CT scans at the same level as Figure 1. Precontrast CT scans (A, C)and selected CT scans from a timedensity study performed after intravenous diatrizoate (B, D) with the indicated area of interest data printed in the lower right of each scan. Four enhancement units (EU) are recorded from the normal psoas skeletal muscle (an increase from 31 to 36; A, B). Four EU are recorded from the pseudotumor (an increase from 38 to 42; C, D). By its anatomic position and a time-density profile and in view of the asymmetric muscle development resulting from as the pyriformis left-sided polio that appeared to affect the pelvis most severely, the “mass ” was established muscle rather than lymphoma.
Time-Density
Analysis
of Pseudotumors 187
Figure 3. Series of CT scans through the upper abdomen of a patient with a history and previous ultrasound study suggestive of a right suprarenal hematoma or abscess. Scans demonstrate the spleen IS), pseudotumor (straight arrow), and left kidney (curved arrow).
gram was negative, but the spinal fluid cytology was positive for lymphoma. A CT scan was requested to evaluate possible interval progression of her lymphoma. The patient gave the additional past medical history of having had polio as a child with more severe involvement of the left lower extremity. The asymmetry of muscular development was evident on physical examination but did not limit her ambulation. Initial scans through the abdomen and pelvis were compared to the earlier CT scan and again identified a soft tissue mass in the right posterolateral pelvis. Figures 1 and 2 demonstrate with an area of interest the mean value increase in CT units of both the skeletal muscle and the pelvic pseudotumor. The skeletal muscle in Figure 1 increased from 31 to 36 CT units (5 EU) and the pseudotumor in Figure 2 increased from 38 to 42 CT units (4 EU). These compar-
Noon and Young 188
able values supported the conclusion that the pseudotumor actually represented a grossly hypertrophied pyriformis muscle. Only the left pyriformis and obturator internus were significantly atrophied as a result of polio, and the resultant asymmetry contributed to the misdiagnosis on the original study. Case 2
A 30-year-old man was a known intravenous drug user who had required a prosthetic aortic valve after endocarditis. He developed acute severe left flank pain and fever. Blood cultures were positive for Candida. Abdominal radiographs and nephrotomograms were negative. A radionuclide DMSA perfusion scan indicated either a small left kidney or a defect in the upper pole. An ultrasound exam identified a mass between the spleen and the upper pole of the left kidney.
A body scan was requested to evaluate the retroperitoneum and the left perinephric area for an abscess. Scans through the abdomen are illustrated in Figure 3 and identify the mass correlating with the ultrasound finding. Following precontrast control scans, the time-density relationships of the pseudotumor and spleen were compared (Figures 4, 5; cf. Figure 6). The close parallel of CT values over time supported the conclusion that the pseudotumor actually represented a variation of splenic anatomy rather than abscess. The patient was spared further invasive procedures as a result. DISCUSSION The pelvic pseudotumor representing a grossly hypertrophied pyriformis muscle in Case 1 was originally misdiagnosed as a manifestation of lymphoma on a previous scan. A time-density analysis performed
with intravenous bolus contrast administration on a subsequent scan demonstrated a pharmacokinetic behavior pattern identical to other muscle groups. This permitted the accurate interpretation of a hypertrophied muscle mass. Dynamic computed tomography body scanning can more precisely define tissue enhancement characteristics by time-density analysis. This technique has been applied to the study of time-density curves in several normal human tissues (5). Although truly dynamic scanning capability was not available in this case, the use of a precontrast control scan and an intravenous bolus of contrast material followed by rapid sequential scans at the same level allowed an estimate of the tissue enhancement pattern. The CT enhancement of skeletal muscle in Case 1 is comparable to that previously reported for muscle (5). Furthermore, a variety of solid tumors have been shown to exhibit contrast enhancement to a higher de-
Figure 4. Selected CT scans of the patient in Figure 3 from the dynamic timedensity sequence. The control scan is in the upper left. The mean CT values in the spleen over time are shown for the area of interest.
Time-Density Analysis of Pseudotumors 189
Figure 5. are virtually
The same CT scans as Figure 4 demonstrating CT values of the pseudotumor identical with those of the spleen in Figure 4.
gree (6). Liposarcomas increased by 11 ELI, which was the smallest increase of the tumors studied, and yet 11 EU is three times greater than the enhancement units observed in normal skeletal muscle (5). Case 2 illustrates the identification of another variation of normal anatomy by time-density analysis. Failure to have correctly interpreted this finding may have resulted in surgical exploration for a presumed abscess. Under similar conditions the clinical
Noon and Young 190
over time. The CT values
staging of malignancy could be seriously altered without proper analysis of the CT findings. Intravenous liposoluble contrast material has recently been used to separate left renal and splenic parenchyma by its selective opacification of liver and spleen (7). By this technique, a lobulated spleen was correctly identified and demarcated from the left kidney, similar to the pseudotumor in Case 2. Although the authors reported failure of water-soluble contrast
Figure 6. Control and post-diatrizoate CT scans at the level of the upper pole of the left kidney demonstrating the difference in X-ray absorption between the left kidney (white) and pseudotumor (Figure 5). Note the characterprofile of istic decrease in CT number (6) of the exophytic right renal cyst (ROI) in contrast with the time-density the pseudotumor (Figure 5).
to solve the diagnostic problem, it was not clear that a time-density analysis following bolus injection was employed, since the time component is crucial in the selective enhancement pattern. A case of differentiating accessory spleen versus left adrenal tumor reported by Stiris (8) required angiography for confirmation. Although the diagnosis was supported by the parallel enhancement of the pseudotumor and spleen following intravenous contrast material, a more rigorous time-density CT study following a bolus injection might have obviated the need for more invasive procedures such as angiography.
material
CONCLUSIONS
These case reports demonstrate the clinical application of CT time-density relationships to solve a diagnostic problem. We propose that analysis of these relationships in the manner described will facilitate correct interpretation in potentially confusing situations. ACKNOWLEDGMENTS
The authors wish to thank Ms. Sue Michalec valuable technical assistance.
REFERENCES
Coin CC, Chan WS: Computed tomographic arteriography. J Comput Assist Tomogr 1: 165-168, 1977 2. Hacker H, Becker H: Time controlled computed tomographic angiography. J Comput Assist Tomogr 1:405409, 1977 3. Norman D, Berninger W, Boyd D, Levin V, Newton 1.
TH: Dynamic computed tomography. Neuroradiology 15:233-234, 1978 4. Young SW, Noon MA, Nassi M, Castellino RA: Dynamic computed tomography body scanning. J Comput Assist Tomogr 4: 16% 173, 1980 5. Young SW, Noon MA, Marincek B: Dynamic computed tomography time-density study of normal human tissue after intravenous contrast administration. Invest Radio1 16:36-39, 1981 6. Young SW, Turner RJ, Castellino RA: A strategy for the contrast enhancement of malignant tumors by utilizing dynamic computed tomography (CT) scanning and intravascular contrast pharmacokinetics. Radiology 137:137-147, 1980 7. Vermess M, Inscoe S, Sugarbarker P: Use of liposoluble contrast material to separate left renal and splenic parenchyma on computed tomography. J Comput Assist Tomogr 4:540-542, 1980 8. Stiris MC: Accessory spleen versus left adrenal tumor: Computed tomographic and abdominal angiographic evaluation. J Comput Assist Tomogr 4:543-544, 1980
for her
Time-Density Analysis of Pseudotumors 191
CONTINUING ANALYSIS
MEDICAL
EDUCATION
IN THE EVALUATION
QUESTIONS
(TIME-DENSITY
OF CT PSEUDOTUMORS)
True or False: 1. 2.
Time-density analysis refers to obtaining dynamic CT scans (or as rapid as possible) before and after the intravenous administration of a bolus of water-soluble contrast medium. Because of the tendency of water-soluble contrast media to diffuse homogeneously throughout the extracellular space, time-density analysis can be adequately performed at any time after an intravenous bolus administration or during a drip infusion of water-soluble contrast media.
Choose the correct statement: 3.
Time-density analysis can be utilized clinically because, following an intravenous bolus of contrast media: a. all normal tissues have a declining X-ray absorption. b. all abnormal tissues demonstrate a slowly increasing CT number. individual tissues or organs have a characteristic time-density profile. C.
True or False: 4.
Because anything that changes the distribution of contrast media within tissues (e.g., occlusion of the main renal artery) can be expected to affect the time-density analysis, normal tissues that have become diseased will change their time-density curves from the expected normal pattern.
Noon and Young 192
scan time) without intravenous contrast agents. At a preselected level through the mass in question, a repeat precontrast control scan was obtained. The patient then received an antecubital intravenous bolus of 50 ml of Renografin-76 (Squibb) followed by scans taken as rapidly as possible (technically limited to approximately every 20 set following the initiation of the bolus). An area of interest was used to measure the Hounsfield CT units and the time-density relationships.
Division of Diagnostic Radiology, Department of Radiology, Stanford University School of Medicine, Stanford, California CT time-density analysis was clinically applied in two case situations in which the etiology of apparent pseudotumors was in question. The enhancement characteristics of these pseudotumors were compared to those of normal tissues, which permitted their correct identification. Time-density analysis was a clinically useful technique in the investigation of unusual CT findings.
CASE REPORTS
Case 1
A most difficult diagnostic task in clinical CT scanning, as in other areas of radiology and medicine, is to distinguish variations of normal from the truly abnormal. With the judicious use of intravenous contrast agents, clinically useful information can be generated by dynamic computed tomography (l-4) and the analysis of the time-density curves (5). These studies demonstrate the clinical usefulness of a time-density analysis of potentially abnormal masses, which were shown by this methodology to be unusual configurations of normal structures. MATERIALS
The patient was a 69-year-old woman admitted for progressive leg weakness and numbness. Thirteen months previously she was diagnosed and treated
AND METHODS
CT scans of the abdomen and pelvis were performed on a GE CT/T 8800 (lo-mm slice thickness, 9.8-set This study was supported in part by grants from the T. F. EckStrom Trust and grants from the NCI, DHEW, CA 24879, and CA 5838. Address correspondence to Stuart W. Young, M.D., Department of Radiology, Stanford University Medical Center, Stanford, California 94305. ‘Present address: Department of Radiology, Scripps Memorial Hospital, 9888 Genesee Avenue, La Jolla, California 92037. ‘Clinical Faculty Fellow, American Cancer Society.
Noon and Young 166
Figure 1. CT scan through the mid-pelvis in a patient with lymphoma and right hip pain. The right-sided pelvic mass (NOW) had been diagnosed on a previous scan in another hospital as recurrent lymphoma.
CT:
the journal of Computed
Tomography,
Copyright
0 University Park Press, 1981 Vol. 5. No. 2, Printed In U.S.A.
with local radiation therapy for a submandibular mass proven by biopsy to represent diffuse histiocytic lymphoma. Other staging procedures, including a lymphangiogram and bone marrow biopsy, were negative. Six months prior to this admission she developed back pain and sweats. In examinations made before she was referred to our institution, a bone scan was
diffusely positive, a bone marrow biopsy was positive for lymphoma, and a CT scan was interpreted as showing a right posterolateral pelvic mass compatible with lymphoma. She was begun on chemotherapy with improvement in her symptomatology. Ten days prior to admission she complained of increasing pain and weakness, especially in her right leg, and required ambuiatory assistance. A myelo-
Figure 2. CT scans at the same level as Figure 1. Precontrast CT scans (A, C)and selected CT scans from a timedensity study performed after intravenous diatrizoate (B, D) with the indicated area of interest data printed in the lower right of each scan. Four enhancement units (EU) are recorded from the normal psoas skeletal muscle (an increase from 31 to 36; A, B). Four EU are recorded from the pseudotumor (an increase from 38 to 42; C, D). By its anatomic position and a time-density profile and in view of the asymmetric muscle development resulting from as the pyriformis left-sided polio that appeared to affect the pelvis most severely, the “mass ” was established muscle rather than lymphoma.
Time-Density
Analysis
of Pseudotumors 187
Figure 3. Series of CT scans through the upper abdomen of a patient with a history and previous ultrasound study suggestive of a right suprarenal hematoma or abscess. Scans demonstrate the spleen IS), pseudotumor (straight arrow), and left kidney (curved arrow).
gram was negative, but the spinal fluid cytology was positive for lymphoma. A CT scan was requested to evaluate possible interval progression of her lymphoma. The patient gave the additional past medical history of having had polio as a child with more severe involvement of the left lower extremity. The asymmetry of muscular development was evident on physical examination but did not limit her ambulation. Initial scans through the abdomen and pelvis were compared to the earlier CT scan and again identified a soft tissue mass in the right posterolateral pelvis. Figures 1 and 2 demonstrate with an area of interest the mean value increase in CT units of both the skeletal muscle and the pelvic pseudotumor. The skeletal muscle in Figure 1 increased from 31 to 36 CT units (5 EU) and the pseudotumor in Figure 2 increased from 38 to 42 CT units (4 EU). These compar-
Noon and Young 188
able values supported the conclusion that the pseudotumor actually represented a grossly hypertrophied pyriformis muscle. Only the left pyriformis and obturator internus were significantly atrophied as a result of polio, and the resultant asymmetry contributed to the misdiagnosis on the original study. Case 2
A 30-year-old man was a known intravenous drug user who had required a prosthetic aortic valve after endocarditis. He developed acute severe left flank pain and fever. Blood cultures were positive for Candida. Abdominal radiographs and nephrotomograms were negative. A radionuclide DMSA perfusion scan indicated either a small left kidney or a defect in the upper pole. An ultrasound exam identified a mass between the spleen and the upper pole of the left kidney.
A body scan was requested to evaluate the retroperitoneum and the left perinephric area for an abscess. Scans through the abdomen are illustrated in Figure 3 and identify the mass correlating with the ultrasound finding. Following precontrast control scans, the time-density relationships of the pseudotumor and spleen were compared (Figures 4, 5; cf. Figure 6). The close parallel of CT values over time supported the conclusion that the pseudotumor actually represented a variation of splenic anatomy rather than abscess. The patient was spared further invasive procedures as a result. DISCUSSION The pelvic pseudotumor representing a grossly hypertrophied pyriformis muscle in Case 1 was originally misdiagnosed as a manifestation of lymphoma on a previous scan. A time-density analysis performed
with intravenous bolus contrast administration on a subsequent scan demonstrated a pharmacokinetic behavior pattern identical to other muscle groups. This permitted the accurate interpretation of a hypertrophied muscle mass. Dynamic computed tomography body scanning can more precisely define tissue enhancement characteristics by time-density analysis. This technique has been applied to the study of time-density curves in several normal human tissues (5). Although truly dynamic scanning capability was not available in this case, the use of a precontrast control scan and an intravenous bolus of contrast material followed by rapid sequential scans at the same level allowed an estimate of the tissue enhancement pattern. The CT enhancement of skeletal muscle in Case 1 is comparable to that previously reported for muscle (5). Furthermore, a variety of solid tumors have been shown to exhibit contrast enhancement to a higher de-
Figure 4. Selected CT scans of the patient in Figure 3 from the dynamic timedensity sequence. The control scan is in the upper left. The mean CT values in the spleen over time are shown for the area of interest.
Time-Density Analysis of Pseudotumors 189
Figure 5. are virtually
The same CT scans as Figure 4 demonstrating CT values of the pseudotumor identical with those of the spleen in Figure 4.
gree (6). Liposarcomas increased by 11 ELI, which was the smallest increase of the tumors studied, and yet 11 EU is three times greater than the enhancement units observed in normal skeletal muscle (5). Case 2 illustrates the identification of another variation of normal anatomy by time-density analysis. Failure to have correctly interpreted this finding may have resulted in surgical exploration for a presumed abscess. Under similar conditions the clinical
Noon and Young 190
over time. The CT values
staging of malignancy could be seriously altered without proper analysis of the CT findings. Intravenous liposoluble contrast material has recently been used to separate left renal and splenic parenchyma by its selective opacification of liver and spleen (7). By this technique, a lobulated spleen was correctly identified and demarcated from the left kidney, similar to the pseudotumor in Case 2. Although the authors reported failure of water-soluble contrast
Figure 6. Control and post-diatrizoate CT scans at the level of the upper pole of the left kidney demonstrating the difference in X-ray absorption between the left kidney (white) and pseudotumor (Figure 5). Note the characterprofile of istic decrease in CT number (6) of the exophytic right renal cyst (ROI) in contrast with the time-density the pseudotumor (Figure 5).
to solve the diagnostic problem, it was not clear that a time-density analysis following bolus injection was employed, since the time component is crucial in the selective enhancement pattern. A case of differentiating accessory spleen versus left adrenal tumor reported by Stiris (8) required angiography for confirmation. Although the diagnosis was supported by the parallel enhancement of the pseudotumor and spleen following intravenous contrast material, a more rigorous time-density CT study following a bolus injection might have obviated the need for more invasive procedures such as angiography.
material
CONCLUSIONS
These case reports demonstrate the clinical application of CT time-density relationships to solve a diagnostic problem. We propose that analysis of these relationships in the manner described will facilitate correct interpretation in potentially confusing situations. ACKNOWLEDGMENTS
The authors wish to thank Ms. Sue Michalec valuable technical assistance.
REFERENCES
Coin CC, Chan WS: Computed tomographic arteriography. J Comput Assist Tomogr 1: 165-168, 1977 2. Hacker H, Becker H: Time controlled computed tomographic angiography. J Comput Assist Tomogr 1:405409, 1977 3. Norman D, Berninger W, Boyd D, Levin V, Newton 1.
TH: Dynamic computed tomography. Neuroradiology 15:233-234, 1978 4. Young SW, Noon MA, Nassi M, Castellino RA: Dynamic computed tomography body scanning. J Comput Assist Tomogr 4: 16% 173, 1980 5. Young SW, Noon MA, Marincek B: Dynamic computed tomography time-density study of normal human tissue after intravenous contrast administration. Invest Radio1 16:36-39, 1981 6. Young SW, Turner RJ, Castellino RA: A strategy for the contrast enhancement of malignant tumors by utilizing dynamic computed tomography (CT) scanning and intravascular contrast pharmacokinetics. Radiology 137:137-147, 1980 7. Vermess M, Inscoe S, Sugarbarker P: Use of liposoluble contrast material to separate left renal and splenic parenchyma on computed tomography. J Comput Assist Tomogr 4:540-542, 1980 8. Stiris MC: Accessory spleen versus left adrenal tumor: Computed tomographic and abdominal angiographic evaluation. J Comput Assist Tomogr 4:543-544, 1980
for her
Time-Density Analysis of Pseudotumors 191
CONTINUING ANALYSIS
MEDICAL
EDUCATION
IN THE EVALUATION
QUESTIONS
(TIME-DENSITY
OF CT PSEUDOTUMORS)
True or False: 1. 2.
Time-density analysis refers to obtaining dynamic CT scans (or as rapid as possible) before and after the intravenous administration of a bolus of water-soluble contrast medium. Because of the tendency of water-soluble contrast media to diffuse homogeneously throughout the extracellular space, time-density analysis can be adequately performed at any time after an intravenous bolus administration or during a drip infusion of water-soluble contrast media.
Choose the correct statement: 3.
Time-density analysis can be utilized clinically because, following an intravenous bolus of contrast media: a. all normal tissues have a declining X-ray absorption. b. all abnormal tissues demonstrate a slowly increasing CT number. individual tissues or organs have a characteristic time-density profile. C.
True or False: 4.
Because anything that changes the distribution of contrast media within tissues (e.g., occlusion of the main renal artery) can be expected to affect the time-density analysis, normal tissues that have become diseased will change their time-density curves from the expected normal pattern.
Noon and Young 192