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Computed tomography findings in clinically normal and abnormal thyroid patients
CT: THE JOURNAL OF COMPUTED TOMOGRAPHY 1985; 9:111-117
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COMPUTED TOMOGRAPHY FINDINGS IN CLINICALLY NORMAL AND ABNORMAL THYROID PATIENTS PETER H. ARGER, MD, ANTHONY S. JENNINGS, MD, LEONARD F. GORDON, MD, BEVERLY G. COLEMAN. LEON AXEL, MD, HERBERT Y. KRESSEL, MD, AND RICHARD L. BARON, MD
Fifty normal volunteers had unenhanced thyroid computed tomography scans. A range of normal computed tomography densities and volumes was established for each age group. Pre- and postcontrast scans were done on 47 abnormal patients with hemorrhagic cysts, multinodular goiter, thyroiditis, papillary carcinoma, and benign adenomas. T h e computed tomography characteristics of each of the pathologic groups was noted for both the abnormal areas and the uninvolved part of the gland. Preliminary observations of the computed tomography characteristics of each abnormality are discussed. KEY WORDS:
Thyroid; Computed tomography; Thyroid carcinoma; Adenoma: Calcification Thyroid imaging techniques are important in the evaluation of thyroid disorders, especially thyroid nodules. Radioisotope scanning gives a two-dimensional image reflecting the thyroid’s functional ability to concentrate and metabolize iodine (1, 2). Lesions less than 0.5 to 1.0 cm are usually not detected. Ultrasound is a sensitive technique for vi-
From the Radiology and Endocrinology Departments, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania; the Radiology Department, Graduate Hospital, Philadelphia, Pennsylvania, and Radiology Associates, Pacific and Colby Building, Everett, Washington. Address reprint requests to: Peter H. Arger, MD, Radiology Department, Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia, Pennsylvania 19104. Received August 1984. 0 198.5 by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Ave., New York, NY 10017 0149-936X/85/$3.30
MD. ’’
sualizing nodules (3-6). Both imaging techniques lack histopathologic specificity. This study was done to evaluate the usefulness of computed tomography (CT) in patients with thyroid disorders. Our purpose was to establish a baseline normal CT appearance of the thyroid by scanning 50 normal subjects. Then, to determine the CT appearance in a variety of pathologic states, we scanned 47 patients with an abnormal thyroid. This report details our findings and puts in perspective our initial impressions. MATERIALS AND METHODS
Fifty normal volunteers, aged 20 to 75 years, had CT scans of their thyroid. The volunteers were ambulatory, had no known thyroid disorder or major medical illness, no history of thyroid irradiation, a negative family history, consumed a normal diet, and were on no medication. They were clinically euthyroid and had no palpable thyroid abnormality. Euthyroidism was confirmed by normal serum thyroxine (TJ, triiodothyronine (T-J, and thyroid-stimulating hormone (TSH) levels. Antimicrosomal antibody titers were negative. In six subjects two scans were performed-one initial scan and one scan after 3 days of oral potassium iodide (KI) ingestion (100 mg each day). The entire thyroid was scanned from top to bottom using contiguous 6-mm sections without contrast injection. The scans were done on a Philips Tomoscan 310 4.8-second scanner with a 256 x 256 matrix. The scan was initiated at the level of the vocal cords. Thyroid tissue was usually visualized 6 to 8 mm below this level. No normal volun-
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teer or patient with an abnormal thyroid scanned in this study had thyroid tissue above this level. In the normal volunteers the following parameters were measured for each lobe: the CT attenuation and the volume (Figures 1 and 2). The CT attenuation and lobe volume was determined by outlining each lobe on each section and utilizing the software features of the Tomoscan 310. For analysis, the volunteers were grouped by decade. All subjects 60 years or older were grouped together.
FIGURE 1. Normal thyroid. Thyroid (T) shows homogeneous density throughout due to normal iodine concentration.
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Forty-seven consecutive patients with thyroid disorders who were clinically euthyroid were scanned initially as described above and then again after the injection of intravenous contrast medium. After an infusion of 75 mL of meglumine iothalamate (Conray 30) was started, 50 mL of meglumine iothalamate (Conray 50) was given in a bolus. A dynamic scan sequence of six contiguous 6-mm scans through the abnormal area was done. Total dynamic scanning time was 2 to 3 minutes. The maximum total contrast medium given was 20 to 24 g of iodine. The CT attenuation was measured in both the abnormal and nodular areas of the thyroid and the uninvolved gland (generally the contralateral lobe) both before and after contrast infusion. The CT characteristics were detailed. The patients were subsequently grouped by diagnosis, which was determined by surgical pathologic specimens; needle aspiration biopsy; or, in patients with thyroiditis, by clinical criteria. Diagnostic groupings were cysts, adenomas, multinodular goiters, carcinomas, thyroiditis and class I on needle aspiration. The data in both normal subjects and abnormal patients were grouped by a range of values, the mean, and the standard deviation (SD) of the mean (see Results). To confirm the accuracy of the volumetric measurements by the software features of the scanner, 30-mL and 50-mL syringes of saline were scanned and their volumes calculated. Both calculations were within less than 5% of the known volume. RESULTS
FIGURE 2. Normal thyroid. Outline of right lobe (A) and left lobe (BJ shows method of obtaining volumes and densities for each side.
In the 47 patients examined, there were the following findings: 9 cysts, 12 goiters, 10 adenomas, 6 thyroiditis, 5 class I cytologies, and 6 carcinomas. The attenuation densities and volumes are shown in Tables 1 and 2. Administration of potassium iodide (100 mg for 3 consecutive days] failed to increase the thyroid density in six normal subjects. The CT characteristics of each histopathologic diTABLE 1. Thyroid Density in Hounsfield No. of Age (yr) cases 20-29 30-39 40-49 50-59 >60
12 11 12 10 5
Range Right
Left
69-118 61-118 59-115 64-98 83-97
70-118 64-118 61-126 54- 96 7s 95
Units
Mean k SD Right Left 104 f 14 102 2 14 86 k 19 87 k 17 94 2 16 94 f 18 88 f 10 85 -c 14 902 6 85-+ 8
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TABLE 2. Thyroid Volume in Cubic Centimeters No. of
Age (yr) cases 20-29 30-39 40-49 50-59 >60
12 11 12 10 5
Right
Range
4.1-8.7 2.7-9.0 2.9-7.8 2.6-8.1 2.5-5.0
Left
2.5-7.1 2.1-8.4 3.2-6.6 1.7-8.3 1.6-3.4
Mean ? SD
Right 6.0 5.0 5.4 3.9 3.9
f -+ 2 -c 2
1.5 1.6 1.6 1.8 1.0
Left
4.9 4.8 4.8 3.3 2.7
+2 f k 2
1.4 1.6 1.4 2.2 0.7
agnosis are summarized below, with the number of cases given in parentheses:
1. Cysts (9)-smooth-walled, homogeneous low-
2.
3.
4.
5.
6.
density mass with enhancing rim of normal thyroid. The rim thickness varied with the size of the cyst and its position within the gland. The mean density change after contrast was 7 Hounsfield units (HU) (Figure 3). The presence of slight wall irregularity and mild inhomogeneity may be related to recent hemorrhage. This was present in one of the nine cases. Adenomas (ll)-soft-tissue range, low-density areas on the unenhanced scan that enhanced in a variable manner. The enhancement ranged from total enhancement of the entire adenoma to a variable pattern of good enhancement inhomogeneously mixed with a poorly enhancing area (Figure 4). Poorly enhancing areas reflected the degree of hemorrhage and necrosis. The mean density change after contrast administration was 44 HU. Nodules were usually single. Multiple nodules were present in only 2 of 11 c a s e s (18%). Calcification was present in only one case (9%). G o i t e r s (12)-similar to adenomas in their unenhanced and enhancement characteristics (Figure 5). The mean density change after contrast was 31 HU. Multiple nodules and calcification were present in 8 of 12 cases (66%). Thyroiditis (5)-three clinically mild to moderately severe cases (Figure 6) showed generalized poor iodine organification throughout the gland on the unenhanced scans. With contrast enhancement, there was a mean density change of 41 HU. The two most severe cases showed focal areas of inhomogeneous enhancement similar to adenomas and goiters. This is presumably due to areas of hemorrhage. Class I (5)-CT patterns similar to goiters and adenomas. The postcontrast mean density change was 21 HU. Carcinomas (6)-CT enhancement pattern evaluation limited by the presence of dense calcifica-
B FIGURE 3. (A) Cyst. Unenhanced scan shows well circumscribed density cyst (C) in left lobe. (B) Cyst. Enhanced scan through same level shows minimal change in density of cyst CC).
tion in two of the six carcinomas. Evaluation of enhancement in these two cases was not believed reliable due to the dense calcification. In the remaining limited series of four cases, the enhancement pattern was of only minimal to moderate peripheral enhancement, with a center that did not enhance or enhanced only a few HU. The inhomogeneous variable enhancement pattern seen in the benign lesions (goiter, adenoma, class I) was not seen in any of the carcinomas (Figures 7 and 8). Calcification was present in three of the six carcinomas (50%). The postcontrast mean density change was 24 H U .
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B
B
FIGURE 5. (A) Goiter. Note low density mass in right thryoid (G). Small amount of normal dense thyroid is seen on left (arrow]. (B) Goiter. Enhanced scan shows variable inhomogeneous enhancement similar to adenomas.
FIGURE 4. (A) Adenoma. Unenhanced scan shows bilat-
eral masses (M) with thin rim of normal tissue (arrows). (B) Adenoma. Enhanced scans show both masses (N) enhancing markedly. The mass on the left has central necrosis. Both biopsies showed benign adenomas.
The pre- and postcontrast densities of the clinically abnormal areas of the patients with thyroid lesions are shown in Table 3. The pre- and postcontrast densities of the uninvolved, ostensibly normal portions of these thyroids fell within the range of normals (Table 1).
DISCUSSION Computed tomography of the thyroid provides excellent visualization of the normal thyroid tissue, which has a higher density than surrounding tissues. This higher density undoubtedly reflects the active uptake, metabolism, and storage of iodine in the thyroid. Thyroid density in normal subjects (Table 1) did not change with advancing age (p < 0.2). The density was always higher than the adjacent soft tissue, such as muscle (40 to 70 HU), and
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B
FIGURE 7. (A) Carcinoma. Unenhanced scan shows a mass in right lobe of thyroid (R) and a second mass in the left lobe (T). (B) Carcinoma. Enhanced scan shows only a moderate degree of enhancement of the masses. At surgery papillary follicular carcinoma was found.
FIGURE 6. Carcinoma. Enhanced scan of huge carcinoma [C) shows an irregular outline but no central enhancement or variable inhomogeneous enhancement seen in the benign lesions. FIGURE 6. (A) Thyroiditis. Unenhanced scans show poor iodination of thyroid gland (T). (B) Thyroiditis. Enhanced scan shows marked enhancement of thyroid (T). was usually 1.5 to a-fold greater. Administration of 100 mg potassium iodide for 3 consecutive days did not further increase the thyroid density in six normal subjects. Therefore, we do not believe that iodide administration is necessary to visualize normal tissue or provide higher contrast between normal and iodine deficient nodules, as has been suggested (7). In our experience, clinically apparent nodules have been seen without iodide administration or contrast medium injection. In several patients, clinically inapparent thyroid abnormalities have likewise been seen. However, variability of iodine ingestion in different geographic areas may affect
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TABLE 3. Abnormal Thyroid Data in Hounsfield Units No. of
Diagnosis
cases
cysts Goiter Adenoma Thyroiditis Class I Carcinoma
9 12 11 5 5 6
Range 9-36 30-86 44-66 42-80 37-67 32-83
Precontrast CT Mean k SD
Range
Postcontrast CT Mean + SD
23 + 10
Zl- 36
56 t 51k 54 f 50 f 71 *
74-109 54-106 84-102 41-105 52-120
thyroid iodine stores and, thus, CT contrast of the thyroid. Evaluation of CT of the thyroid in other areas of the country and world is necessary to determine this. Because of the sharply defined thyroid and the computer software capabilities, the thyroid volume of each lobe can be accurately determined. In our group of 50 normal subjects, the right lobe was consistently slightly larger than the left lobe in all age groups. The volumes of both lobes decreased with advancing age (p < 0.05). Linear regression analysis shows a significant correlation coefficient of 0.9. These volumes (Table 2) agree with determinations of thyroid size and weight in surgical and autopsy specimens previously cited in the literature (8-10) and provide a standard reference for use in evaluating abnormal thyroids. The normal volume data has been helpful clinically in situations where palpation does not adequately determine if the palpable gland is mildly enlarged. Computed tomography volume analysis is very helpful in sizing a small goiter and estimating how close it is to normal size. The early impression of our collaborating endocrinologists is that CT is the best way to size these patients’ goiters. The CT volume seems also to be of value in treating hyperthyroidism by providing an accurate thyroid volume estimation for iodine dose calculations. From our preliminary data in patients with thyroid abnormalities, CT has several desirable characteristics. Both normal and abnormal portions of the thyroid are seen, and the size and volume of lobes or nodules can be easily, accurately, and reproducibily determined. The high resolution of this technique allows lesions 3 to 4 mm in size to be visualized. We have found CT to be particularly useful in evaluating the extent of substernal goiters or lesions that clinically appeared to be causing compressing symptoms of the trachea or esophagus. Also, CT is able to distinguish neck lesions external to the thyroid such as lipomas, lymph nodes, etc. This can be extremely valuable in resolving any confusion regarding the site of origin of palpable masses.
11 9 14 12 19
30f 87 r+ 91 2 95f 71 f 96 -c
6 14 19 6 23 26
Mean Change 7 31 44 41 21 24
The numbers in this series, especially for the carcinomas, are small. Though no definite conclusions can be made, in analyzing the CT characteristics as described in the Results section, some preliminary observations are possible. The presence of calcifications does not help in distinguishing benign and malignant disease. Calcification was present in 50% of carcinomas and 66% of goiters. Calcifications can be helpful by being used as a guide for the site of biopsy. The unenhanced baseline attenuation values of both benign and malignant disease were similar except for cysts and areas of necrosis, which were lower. The baseline attenuation value of cysts had a mean of 23 HU, whereas all other abnormalities had values of 40 HU or above. Unsuspected areas of necrosis within the noncystic abnormalities were in part responsible for the range variation of unenhanced density. For cysts, the unenhanced density may vary depending upon the presence and degree of internal hemorrhage. Cysts and areas of necrosis enhance minimally with a mean under 10 HU (Figure 3). There also was some variability and overlap among the various benign and malignant lesions after contrast medium administration. Using only the range and mean density of the benign and malignant lesions both before and after contrast medium administration, no discriminating features are suggested. However, analyzing the density change after contrast medium administration suggests one feature. The mean change of carcinomas, class I lesions, goiters, adenomas, and thyroiditis were 24, 21, 32, 44, and 41 HU, respectively. The greater degree of enhancement tended to be in the benign lesions. This is borne out by analyzing the specific individual postcontrast attenuation changes of the six carcinomas. None had a density change greater than 37 HU. Only one carcinoma had an enhancement change of more than 30 HU. In analyzing the individual benign lesion density change, 40% had a change of more than 40 H U . This suggests that when a lesion enhances more
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than 40 HU and no calcification is present, a benign lesion is suggested. An adenoma or focal thyroiditis are most likely. Evaluation of more thyroid carcinomas is needed to test the above observation of higher density change tendency in benign lesions, as well as the observation of enhancement patterns. The number of carcinomas in this series is too low to do other than suggest that benign lesions tend to enhance in the inhomogeneous pattern described and illustrated (Figures 4 and 5), whereas the few carcinomas enhanced only peripherally when enhancement was present. Certainly further investigation is needed to see if these very preliminary observations will be sustained over larger number of lesions. In evaluating the uninvolved areas of the abnormal glands, there was again considerable variation of both the pre- and postcontrast uninvolved gland. The variability depended upon the degree of iodination of the uninvolved gland. In the unenhanced scans, the attenuation value of the uninvolved portions of the thyroid usually fell within the normal range for that age group. The density change of the uninvolved portions due to enhancement had a mean of 32 HU. Greater enhancement occurred when the initial density was in the low normal range. Less enhancement was present when the initial density was high. In conclusion, we believe our investigation of normal and abnormal thyroids has established a reference for density and volume of the normal thyroid by CT (11-13). We have suggested some preliminary observations regarding the abnormal thyroid including the use of CT as an excellent guide to the size and extent of a lesion, especially its substernal extent; the use of volumes in planning iodine therapy; and the use of CT in distinguishing between thyroid and nonthyroid lesions. Some preliminary observations on the CT characteristics of benign and malignant lesions suggest the need for further investigation as to whether CT can be more specific in distinguishing these entities. REFERENCES Keyes JW, Thrall JH, Carey JE: Technical considerations in in vivo thyroid studies. Semin Nucl Med 1978;8:43-57. Sisson JC, Partold SP, Bartold SL: The dilemma of the solitary thyroid nodule: Resolution through decision analysis. Semin Nucl Med 1978;8:59-71. Chilcote WS: Gray scale ultrasonography of the thyroid. Radiology 1976;120:381-3. Sackler JP, Passalaqua AM, Blum M, Amorocho L: A spectrum of diseases of the thyroid gland as imaged by gray scale water bath sonography. Radiology 1977;125:467-72.
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5. Scheible W, Leopold GR, Woo VL, Gosink BB: High resolution realtime ultrasonography of thyroid nodules. Radiology 1979;133:413-7. 6. Simeone JF, Daniels GH, Mueller PR, et al.: High resolution real-time sonography of the thyroid. Radiology 1982; 145:431-5. 7. Lips CJM, Vette JK, Ruys JHJ, et al.: Letter to Editor. N Engl J Med 1982;306:1491. 8. Marine D: The present status of the functions of the thyroid gland. Physiol Rev 1922;2:521-51. 9. Marine D, Lenhart CH: The pathological anatomy of the human thyroid gland. Arch Intern Med 1911;7:506-35. 10 Meissner WA, Warren S: Tumors of the thyroid gland. Atlas of tumor pathology, series 2, fascicle 4. Washington, DC: Armed Forces Institute of Pathology 1968:13-23. 11. Barnes D, Young SW: CT attenuation of the thyroid gland and clinical applications. Presented at the Associati& of Universitv Radioloaists Annual Meeting. New Orleans. Louisiana, April 1981.“ 12 Kaneko T, Matsumoto M, Fukui K, et al.: Clinical evaluation of thyroid CT values in various clinical conditions. CT 1979; 3:1-4. 13 Wolf BS, Nakagawa H, Yeh HC: Visualization of the thyroid gland with computed tomography. Radiology 1977;123:368.
CONTINUING MEDICAL EDUCATION QUESTIONS 1. Normal thyroid volumes are not helpful in which of
the following situations? a. Sizing a small thyroid goiter. b. Hyperthyroidism. c. Volume estimation for iodine dose calculations. d. Sizing of a multinodular goiter. 2. The unenhanced baseline attenuation values of benign and malignant thyroid lesions were similar except for which of the following? a. Adenomas. b. Cysts. c. Thyroid cancer. d. Goiters. 3. Which one of the following statements is correct? a. Benign lesions tend to enhance to a greater degree than malignant lesions. b. All thyroid lesions except cysts enhance to the same degree. C. The range and mean density of the lesions alone enabled some discriminating features between benign and malignant lesions. d. The mean density change after contrast was higher in malignant lesions. 4. Computed tomography of the thyroid can provide all but which of the followina? A reference for densitiand volume of normal thyroids. An excellent guide to the size and extent of the thyroid lesion. Help in planning iodine therapy. Distinction between benign and malignant disease.
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COMPUTED TOMOGRAPHY FINDINGS IN CLINICALLY NORMAL AND ABNORMAL THYROID PATIENTS PETER H. ARGER, MD, ANTHONY S. JENNINGS, MD, LEONARD F. GORDON, MD, BEVERLY G. COLEMAN. LEON AXEL, MD, HERBERT Y. KRESSEL, MD, AND RICHARD L. BARON, MD
Fifty normal volunteers had unenhanced thyroid computed tomography scans. A range of normal computed tomography densities and volumes was established for each age group. Pre- and postcontrast scans were done on 47 abnormal patients with hemorrhagic cysts, multinodular goiter, thyroiditis, papillary carcinoma, and benign adenomas. T h e computed tomography characteristics of each of the pathologic groups was noted for both the abnormal areas and the uninvolved part of the gland. Preliminary observations of the computed tomography characteristics of each abnormality are discussed. KEY WORDS:
Thyroid; Computed tomography; Thyroid carcinoma; Adenoma: Calcification Thyroid imaging techniques are important in the evaluation of thyroid disorders, especially thyroid nodules. Radioisotope scanning gives a two-dimensional image reflecting the thyroid’s functional ability to concentrate and metabolize iodine (1, 2). Lesions less than 0.5 to 1.0 cm are usually not detected. Ultrasound is a sensitive technique for vi-
From the Radiology and Endocrinology Departments, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania; the Radiology Department, Graduate Hospital, Philadelphia, Pennsylvania, and Radiology Associates, Pacific and Colby Building, Everett, Washington. Address reprint requests to: Peter H. Arger, MD, Radiology Department, Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia, Pennsylvania 19104. Received August 1984. 0 198.5 by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Ave., New York, NY 10017 0149-936X/85/$3.30
MD. ’’
sualizing nodules (3-6). Both imaging techniques lack histopathologic specificity. This study was done to evaluate the usefulness of computed tomography (CT) in patients with thyroid disorders. Our purpose was to establish a baseline normal CT appearance of the thyroid by scanning 50 normal subjects. Then, to determine the CT appearance in a variety of pathologic states, we scanned 47 patients with an abnormal thyroid. This report details our findings and puts in perspective our initial impressions. MATERIALS AND METHODS
Fifty normal volunteers, aged 20 to 75 years, had CT scans of their thyroid. The volunteers were ambulatory, had no known thyroid disorder or major medical illness, no history of thyroid irradiation, a negative family history, consumed a normal diet, and were on no medication. They were clinically euthyroid and had no palpable thyroid abnormality. Euthyroidism was confirmed by normal serum thyroxine (TJ, triiodothyronine (T-J, and thyroid-stimulating hormone (TSH) levels. Antimicrosomal antibody titers were negative. In six subjects two scans were performed-one initial scan and one scan after 3 days of oral potassium iodide (KI) ingestion (100 mg each day). The entire thyroid was scanned from top to bottom using contiguous 6-mm sections without contrast injection. The scans were done on a Philips Tomoscan 310 4.8-second scanner with a 256 x 256 matrix. The scan was initiated at the level of the vocal cords. Thyroid tissue was usually visualized 6 to 8 mm below this level. No normal volun-
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ARGER ET AL.
teer or patient with an abnormal thyroid scanned in this study had thyroid tissue above this level. In the normal volunteers the following parameters were measured for each lobe: the CT attenuation and the volume (Figures 1 and 2). The CT attenuation and lobe volume was determined by outlining each lobe on each section and utilizing the software features of the Tomoscan 310. For analysis, the volunteers were grouped by decade. All subjects 60 years or older were grouped together.
FIGURE 1. Normal thyroid. Thyroid (T) shows homogeneous density throughout due to normal iodine concentration.
CT: THE JOURNAL OF COMPUTED TOMOGRAPHY VOL. 9 NO. 2
Forty-seven consecutive patients with thyroid disorders who were clinically euthyroid were scanned initially as described above and then again after the injection of intravenous contrast medium. After an infusion of 75 mL of meglumine iothalamate (Conray 30) was started, 50 mL of meglumine iothalamate (Conray 50) was given in a bolus. A dynamic scan sequence of six contiguous 6-mm scans through the abnormal area was done. Total dynamic scanning time was 2 to 3 minutes. The maximum total contrast medium given was 20 to 24 g of iodine. The CT attenuation was measured in both the abnormal and nodular areas of the thyroid and the uninvolved gland (generally the contralateral lobe) both before and after contrast infusion. The CT characteristics were detailed. The patients were subsequently grouped by diagnosis, which was determined by surgical pathologic specimens; needle aspiration biopsy; or, in patients with thyroiditis, by clinical criteria. Diagnostic groupings were cysts, adenomas, multinodular goiters, carcinomas, thyroiditis and class I on needle aspiration. The data in both normal subjects and abnormal patients were grouped by a range of values, the mean, and the standard deviation (SD) of the mean (see Results). To confirm the accuracy of the volumetric measurements by the software features of the scanner, 30-mL and 50-mL syringes of saline were scanned and their volumes calculated. Both calculations were within less than 5% of the known volume. RESULTS
FIGURE 2. Normal thyroid. Outline of right lobe (A) and left lobe (BJ shows method of obtaining volumes and densities for each side.
In the 47 patients examined, there were the following findings: 9 cysts, 12 goiters, 10 adenomas, 6 thyroiditis, 5 class I cytologies, and 6 carcinomas. The attenuation densities and volumes are shown in Tables 1 and 2. Administration of potassium iodide (100 mg for 3 consecutive days] failed to increase the thyroid density in six normal subjects. The CT characteristics of each histopathologic diTABLE 1. Thyroid Density in Hounsfield No. of Age (yr) cases 20-29 30-39 40-49 50-59 >60
12 11 12 10 5
Range Right
Left
69-118 61-118 59-115 64-98 83-97
70-118 64-118 61-126 54- 96 7s 95
Units
Mean k SD Right Left 104 f 14 102 2 14 86 k 19 87 k 17 94 2 16 94 f 18 88 f 10 85 -c 14 902 6 85-+ 8
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TABLE 2. Thyroid Volume in Cubic Centimeters No. of
Age (yr) cases 20-29 30-39 40-49 50-59 >60
12 11 12 10 5
Right
Range
4.1-8.7 2.7-9.0 2.9-7.8 2.6-8.1 2.5-5.0
Left
2.5-7.1 2.1-8.4 3.2-6.6 1.7-8.3 1.6-3.4
Mean ? SD
Right 6.0 5.0 5.4 3.9 3.9
f -+ 2 -c 2
1.5 1.6 1.6 1.8 1.0
Left
4.9 4.8 4.8 3.3 2.7
+2 f k 2
1.4 1.6 1.4 2.2 0.7
agnosis are summarized below, with the number of cases given in parentheses:
1. Cysts (9)-smooth-walled, homogeneous low-
2.
3.
4.
5.
6.
density mass with enhancing rim of normal thyroid. The rim thickness varied with the size of the cyst and its position within the gland. The mean density change after contrast was 7 Hounsfield units (HU) (Figure 3). The presence of slight wall irregularity and mild inhomogeneity may be related to recent hemorrhage. This was present in one of the nine cases. Adenomas (ll)-soft-tissue range, low-density areas on the unenhanced scan that enhanced in a variable manner. The enhancement ranged from total enhancement of the entire adenoma to a variable pattern of good enhancement inhomogeneously mixed with a poorly enhancing area (Figure 4). Poorly enhancing areas reflected the degree of hemorrhage and necrosis. The mean density change after contrast administration was 44 HU. Nodules were usually single. Multiple nodules were present in only 2 of 11 c a s e s (18%). Calcification was present in only one case (9%). G o i t e r s (12)-similar to adenomas in their unenhanced and enhancement characteristics (Figure 5). The mean density change after contrast was 31 HU. Multiple nodules and calcification were present in 8 of 12 cases (66%). Thyroiditis (5)-three clinically mild to moderately severe cases (Figure 6) showed generalized poor iodine organification throughout the gland on the unenhanced scans. With contrast enhancement, there was a mean density change of 41 HU. The two most severe cases showed focal areas of inhomogeneous enhancement similar to adenomas and goiters. This is presumably due to areas of hemorrhage. Class I (5)-CT patterns similar to goiters and adenomas. The postcontrast mean density change was 21 HU. Carcinomas (6)-CT enhancement pattern evaluation limited by the presence of dense calcifica-
B FIGURE 3. (A) Cyst. Unenhanced scan shows well circumscribed density cyst (C) in left lobe. (B) Cyst. Enhanced scan through same level shows minimal change in density of cyst CC).
tion in two of the six carcinomas. Evaluation of enhancement in these two cases was not believed reliable due to the dense calcification. In the remaining limited series of four cases, the enhancement pattern was of only minimal to moderate peripheral enhancement, with a center that did not enhance or enhanced only a few HU. The inhomogeneous variable enhancement pattern seen in the benign lesions (goiter, adenoma, class I) was not seen in any of the carcinomas (Figures 7 and 8). Calcification was present in three of the six carcinomas (50%). The postcontrast mean density change was 24 H U .
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B
B
FIGURE 5. (A) Goiter. Note low density mass in right thryoid (G). Small amount of normal dense thyroid is seen on left (arrow]. (B) Goiter. Enhanced scan shows variable inhomogeneous enhancement similar to adenomas.
FIGURE 4. (A) Adenoma. Unenhanced scan shows bilat-
eral masses (M) with thin rim of normal tissue (arrows). (B) Adenoma. Enhanced scans show both masses (N) enhancing markedly. The mass on the left has central necrosis. Both biopsies showed benign adenomas.
The pre- and postcontrast densities of the clinically abnormal areas of the patients with thyroid lesions are shown in Table 3. The pre- and postcontrast densities of the uninvolved, ostensibly normal portions of these thyroids fell within the range of normals (Table 1).
DISCUSSION Computed tomography of the thyroid provides excellent visualization of the normal thyroid tissue, which has a higher density than surrounding tissues. This higher density undoubtedly reflects the active uptake, metabolism, and storage of iodine in the thyroid. Thyroid density in normal subjects (Table 1) did not change with advancing age (p < 0.2). The density was always higher than the adjacent soft tissue, such as muscle (40 to 70 HU), and
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B
FIGURE 7. (A) Carcinoma. Unenhanced scan shows a mass in right lobe of thyroid (R) and a second mass in the left lobe (T). (B) Carcinoma. Enhanced scan shows only a moderate degree of enhancement of the masses. At surgery papillary follicular carcinoma was found.
FIGURE 6. Carcinoma. Enhanced scan of huge carcinoma [C) shows an irregular outline but no central enhancement or variable inhomogeneous enhancement seen in the benign lesions. FIGURE 6. (A) Thyroiditis. Unenhanced scans show poor iodination of thyroid gland (T). (B) Thyroiditis. Enhanced scan shows marked enhancement of thyroid (T). was usually 1.5 to a-fold greater. Administration of 100 mg potassium iodide for 3 consecutive days did not further increase the thyroid density in six normal subjects. Therefore, we do not believe that iodide administration is necessary to visualize normal tissue or provide higher contrast between normal and iodine deficient nodules, as has been suggested (7). In our experience, clinically apparent nodules have been seen without iodide administration or contrast medium injection. In several patients, clinically inapparent thyroid abnormalities have likewise been seen. However, variability of iodine ingestion in different geographic areas may affect
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TABLE 3. Abnormal Thyroid Data in Hounsfield Units No. of
Diagnosis
cases
cysts Goiter Adenoma Thyroiditis Class I Carcinoma
9 12 11 5 5 6
Range 9-36 30-86 44-66 42-80 37-67 32-83
Precontrast CT Mean k SD
Range
Postcontrast CT Mean + SD
23 + 10
Zl- 36
56 t 51k 54 f 50 f 71 *
74-109 54-106 84-102 41-105 52-120
thyroid iodine stores and, thus, CT contrast of the thyroid. Evaluation of CT of the thyroid in other areas of the country and world is necessary to determine this. Because of the sharply defined thyroid and the computer software capabilities, the thyroid volume of each lobe can be accurately determined. In our group of 50 normal subjects, the right lobe was consistently slightly larger than the left lobe in all age groups. The volumes of both lobes decreased with advancing age (p < 0.05). Linear regression analysis shows a significant correlation coefficient of 0.9. These volumes (Table 2) agree with determinations of thyroid size and weight in surgical and autopsy specimens previously cited in the literature (8-10) and provide a standard reference for use in evaluating abnormal thyroids. The normal volume data has been helpful clinically in situations where palpation does not adequately determine if the palpable gland is mildly enlarged. Computed tomography volume analysis is very helpful in sizing a small goiter and estimating how close it is to normal size. The early impression of our collaborating endocrinologists is that CT is the best way to size these patients’ goiters. The CT volume seems also to be of value in treating hyperthyroidism by providing an accurate thyroid volume estimation for iodine dose calculations. From our preliminary data in patients with thyroid abnormalities, CT has several desirable characteristics. Both normal and abnormal portions of the thyroid are seen, and the size and volume of lobes or nodules can be easily, accurately, and reproducibily determined. The high resolution of this technique allows lesions 3 to 4 mm in size to be visualized. We have found CT to be particularly useful in evaluating the extent of substernal goiters or lesions that clinically appeared to be causing compressing symptoms of the trachea or esophagus. Also, CT is able to distinguish neck lesions external to the thyroid such as lipomas, lymph nodes, etc. This can be extremely valuable in resolving any confusion regarding the site of origin of palpable masses.
11 9 14 12 19
30f 87 r+ 91 2 95f 71 f 96 -c
6 14 19 6 23 26
Mean Change 7 31 44 41 21 24
The numbers in this series, especially for the carcinomas, are small. Though no definite conclusions can be made, in analyzing the CT characteristics as described in the Results section, some preliminary observations are possible. The presence of calcifications does not help in distinguishing benign and malignant disease. Calcification was present in 50% of carcinomas and 66% of goiters. Calcifications can be helpful by being used as a guide for the site of biopsy. The unenhanced baseline attenuation values of both benign and malignant disease were similar except for cysts and areas of necrosis, which were lower. The baseline attenuation value of cysts had a mean of 23 HU, whereas all other abnormalities had values of 40 HU or above. Unsuspected areas of necrosis within the noncystic abnormalities were in part responsible for the range variation of unenhanced density. For cysts, the unenhanced density may vary depending upon the presence and degree of internal hemorrhage. Cysts and areas of necrosis enhance minimally with a mean under 10 HU (Figure 3). There also was some variability and overlap among the various benign and malignant lesions after contrast medium administration. Using only the range and mean density of the benign and malignant lesions both before and after contrast medium administration, no discriminating features are suggested. However, analyzing the density change after contrast medium administration suggests one feature. The mean change of carcinomas, class I lesions, goiters, adenomas, and thyroiditis were 24, 21, 32, 44, and 41 HU, respectively. The greater degree of enhancement tended to be in the benign lesions. This is borne out by analyzing the specific individual postcontrast attenuation changes of the six carcinomas. None had a density change greater than 37 HU. Only one carcinoma had an enhancement change of more than 30 HU. In analyzing the individual benign lesion density change, 40% had a change of more than 40 H U . This suggests that when a lesion enhances more
APRIL 1985
than 40 HU and no calcification is present, a benign lesion is suggested. An adenoma or focal thyroiditis are most likely. Evaluation of more thyroid carcinomas is needed to test the above observation of higher density change tendency in benign lesions, as well as the observation of enhancement patterns. The number of carcinomas in this series is too low to do other than suggest that benign lesions tend to enhance in the inhomogeneous pattern described and illustrated (Figures 4 and 5), whereas the few carcinomas enhanced only peripherally when enhancement was present. Certainly further investigation is needed to see if these very preliminary observations will be sustained over larger number of lesions. In evaluating the uninvolved areas of the abnormal glands, there was again considerable variation of both the pre- and postcontrast uninvolved gland. The variability depended upon the degree of iodination of the uninvolved gland. In the unenhanced scans, the attenuation value of the uninvolved portions of the thyroid usually fell within the normal range for that age group. The density change of the uninvolved portions due to enhancement had a mean of 32 HU. Greater enhancement occurred when the initial density was in the low normal range. Less enhancement was present when the initial density was high. In conclusion, we believe our investigation of normal and abnormal thyroids has established a reference for density and volume of the normal thyroid by CT (11-13). We have suggested some preliminary observations regarding the abnormal thyroid including the use of CT as an excellent guide to the size and extent of a lesion, especially its substernal extent; the use of volumes in planning iodine therapy; and the use of CT in distinguishing between thyroid and nonthyroid lesions. Some preliminary observations on the CT characteristics of benign and malignant lesions suggest the need for further investigation as to whether CT can be more specific in distinguishing these entities. REFERENCES Keyes JW, Thrall JH, Carey JE: Technical considerations in in vivo thyroid studies. Semin Nucl Med 1978;8:43-57. Sisson JC, Partold SP, Bartold SL: The dilemma of the solitary thyroid nodule: Resolution through decision analysis. Semin Nucl Med 1978;8:59-71. Chilcote WS: Gray scale ultrasonography of the thyroid. Radiology 1976;120:381-3. Sackler JP, Passalaqua AM, Blum M, Amorocho L: A spectrum of diseases of the thyroid gland as imaged by gray scale water bath sonography. Radiology 1977;125:467-72.
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5. Scheible W, Leopold GR, Woo VL, Gosink BB: High resolution realtime ultrasonography of thyroid nodules. Radiology 1979;133:413-7. 6. Simeone JF, Daniels GH, Mueller PR, et al.: High resolution real-time sonography of the thyroid. Radiology 1982; 145:431-5. 7. Lips CJM, Vette JK, Ruys JHJ, et al.: Letter to Editor. N Engl J Med 1982;306:1491. 8. Marine D: The present status of the functions of the thyroid gland. Physiol Rev 1922;2:521-51. 9. Marine D, Lenhart CH: The pathological anatomy of the human thyroid gland. Arch Intern Med 1911;7:506-35. 10 Meissner WA, Warren S: Tumors of the thyroid gland. Atlas of tumor pathology, series 2, fascicle 4. Washington, DC: Armed Forces Institute of Pathology 1968:13-23. 11. Barnes D, Young SW: CT attenuation of the thyroid gland and clinical applications. Presented at the Associati& of Universitv Radioloaists Annual Meeting. New Orleans. Louisiana, April 1981.“ 12 Kaneko T, Matsumoto M, Fukui K, et al.: Clinical evaluation of thyroid CT values in various clinical conditions. CT 1979; 3:1-4. 13 Wolf BS, Nakagawa H, Yeh HC: Visualization of the thyroid gland with computed tomography. Radiology 1977;123:368.
CONTINUING MEDICAL EDUCATION QUESTIONS 1. Normal thyroid volumes are not helpful in which of
the following situations? a. Sizing a small thyroid goiter. b. Hyperthyroidism. c. Volume estimation for iodine dose calculations. d. Sizing of a multinodular goiter. 2. The unenhanced baseline attenuation values of benign and malignant thyroid lesions were similar except for which of the following? a. Adenomas. b. Cysts. c. Thyroid cancer. d. Goiters. 3. Which one of the following statements is correct? a. Benign lesions tend to enhance to a greater degree than malignant lesions. b. All thyroid lesions except cysts enhance to the same degree. C. The range and mean density of the lesions alone enabled some discriminating features between benign and malignant lesions. d. The mean density change after contrast was higher in malignant lesions. 4. Computed tomography of the thyroid can provide all but which of the followina? A reference for densitiand volume of normal thyroids. An excellent guide to the size and extent of the thyroid lesion. Help in planning iodine therapy. Distinction between benign and malignant disease.