How Large Are These Thyroid Glands?
For each of the following patients, assessment of thyroid size is an important part of the clinical examination. In case 1, a 32-year-old woman presents with symptoms and findings consistent with hyperthyroidism, but she has no exophthalmos and has always been anxious. In case 2, a 55-year-old man has a diagnosis of Graves disease, and the choice is made for radioactive iodine ablation therapy. In case 3, a 64-year-old man has a goiter that causes discomfort on swallowing, and thyroxine is administered in an attempt to shrink the thyroid gland.
Why Assess the Thyroid Gland for Size?
A goiter is simply an enlargement of the thyroid gland and may result from hormonal or immunologic stimulation of gland growth or the presence of inflammatory, proliferative, infiltrative, or metabolic disorders (Table 21-1). A common error among clinicians first learning about the thyroid is to associate thyroid size with function; a goiter, however, can be present in hyperthyroidism, hypothyroidism, or a euthyroid state. Determining whether a thyroid is enlarged can aid in diagnosis, differential diagnosis, and decisions about laboratory testing; in determining specific therapy and therapeutic dosing; and subsequently in monitoring of the clinical course. For example, when a patient presents with symptoms that could be caused by hyperthyroidism, the detection of a goiter increases the likelihood that thyrotoxicosis is present.2 If the patient described in the first case had an enlarged thyroid, hyperthyroidism would be a likely diagnosis.2 On the other hand, if her gland were of normal size, anxiety might be the explanation for her symptoms. Determination of thyroid size also is useful once a specific disease is diagnosed. In patients with Graves disease, for example, thyroid size may be a factor in determining choice of treatment because patients with smaller glands are more likely to go into immunologic remission during antithyroid drug therapy.3 If radioiodine is the chosen treatment, as in the second case, the size of the gland is often used in calculating the dose to be administered.4 Finally, responses to various therapies can be monitored clinically by assessing thyroid size, such as the attempt to shrink a large goiter with thyroid hormone administration in the third case.5
Table 21-1.Conditions That May Present With an Enlarged Thyroid Glanda |Favorite Table|Download (.pdf) Table 21-1. Conditions That May Present With an Enlarged Thyroid Glanda
|Endemic/iodine deficiency goiter |
|Multinodular goiter |
|Graves disease |
|Hashimoto thyroiditis |
|Subacute thyroiditis |
|Painless/postpartum thyroiditis |
|Familial goiter |
|Iodine excess |
The Anatomic Basis of Thyroid Examination
Landmarks and Relation to Other Structures
The thyroid gland is located in the anterior neck and usually consists of 2 lobes connected at their lower midregions by a transverse isthmus (Figure 21-1). The most prominent structure in the anterior neck is the thyroid cartilage. Inferior to the thyroid cartilage lies the cricoid cartilage, and inferior to this lies the isthmus of the thyroid gland, which can be as low as the level of the fourth tracheal ring. Each thyroid lobe lies against the sides of the trachea, extending up from the isthmus to the region of the cricoid and thyroid cartilages and downward toward the clavicles. The posterior portion of each lobe lies beneath the belly of the ipsilateral sternocleidomastoid muscle. Because the fascial envelope of the thyroid gland is continuous with the pretracheal fascia of the cricoid cartilage and hyoid bone, the thyroid ascends and descends with the laryngeal structures during swallowing.
The Location of the Thyroid Gland in Relationship to Nearby Structures
How Large Is the Normal Thyroid?
The normal thyroid size for a population is largely determined by the supply of iodine in the diet, with a tendency to larger glands in iodine-deficient areas.6, 7, and 8 Consequently, studies of clinically normal thyroid glands have demonstrated sizes that span an extreme range in euthyroid individuals, differing by geographic location and varying through time within a given region as iodine supplementation has been instituted. Until the middle of this century, most authors considered a typical thyroid gland to be about 20-25 g, and a commonly accepted upper normal size was 35 g.8, 9, 10, and 11 More recent studies in iodine-supplemented populations have reported mean weights of 10 g or less and an upper normal size of 20 g.12, 13 Although a value of 35 g may still apply in iodine-deficient areas, an upper normal weight of 20 g is probably appropriate for most parts of the western world and will be used for this analysis. With this definition, the prevalence of goiter is typically 2% to 5% in iodine-replete regions.13, 14
How to Examine the Thyroid Gland to Determine Size
The normal thyroid is rarely visible because of its relatively small size, partial concealment by the sternocleidomastoids, and soft texture, and it may be marginally palpable.5, 9, 15 Enlargement is initially observed as an increase in the size of the lateral lobes to palpation.5, 8 Further growth results in a gland visible in the anterior side of the neck that can be seen when inspecting from the side16, 17 and from the front with the patient's neck extended.5, 7, 15, 18 With increasing size, the gland becomes even more prominent on inspection from the side and it becomes visible from the front with the patient's head in a normal position. Ultimately, a large goiter is easily palpable, has prominence from the side of greater than 1 cm, and is visible from the front at a distance.5, 17, 18
As a result of observations on these patterns of enlargement, various systems have been described to size a thyroid gland according to (1) the estimated weight19, 20, and 21; (2) the volume relative to the size of normal glands5, 8; (3) the presence or absence of palpable or visible enlargement8, 18, 22; (4) the degree of visible prominence when the neck is viewed laterally17; (5) neck circumference determined by tape measure23, 24; (6) the surface area of the gland projected onto the skin22, 25; and (7) the maximum width of the lower poles, measured with a ruler or calipers.26 Many of these rating scales were developed for epidemiologic studies of goiter in endemic areas and were intended to classify significant goiters rapidly (with examination time in some studies averaging only 18 seconds per subject).5 As a result, many are of little use for the smaller thyroid glands observed in regions without significant levels of endemic goiter. Most studies from which data for accuracy and precision of goiter determination can be derived do not report specifics of thyroid examination technique. Consequently, there is no objective evidence to support the use of one examination method over another.23, 24, and 25, 27, 28 Many of the variations are minor, so shared features will be described.
The patient should be comfortably positioned, either standing or seated, with the neck in a neutral position or slightly extended. The region of the neck below the thyroid or cricoid cartilage should be observed from the front, with good cross-lighting to accentuate shadows and highlight masses. If an abnormality is suspected, the neck should be moved as appropriate to alter the prominence of the area under suspicion. A particularly useful maneuver is inspection during full extension of the patient's neck. This position stretches superficial tissues over the thyroid gland, which is pressed against the relatively unyielding trachea, and enhances visibility of the gland. Inspection of the neck from the side, looking for a prominence protruding from the normally smooth and straight contour between the cricoid cartilage and the suprasternal notch, can reveal enlargement.17 The amount of prominence should be measured with a ruler (Figure 21-2). This method requires a certain degree of guesswork in deducing where the normal neck contour would lie, but the measurement can provide information useful for ruling in the presence of a goiter. There is no particular spot to place the ruler; it merely serves as a visual guide in estimating the degree of protrusion.
Estimating Lateral Thyroid Prominence
When viewed from the side, the normal contour of the thyroid gland is invisible. Enlargement up and out leads to a prominent and visible gland.
After inspection, the gland is palpated, and this is where the greatest differences in methods arise. Clinician preference varies about palpation with fingers or thumbs, an approach from the front or from behind the patient, and whether each lobe is palpated by the ipsilateral hand or the opposite hand. In the absence of data to support a specific method, though, examiners should use the approach with which they are most comfortable. Regardless of the technique used, it is often useful to first attempt to locate the thyroid isthmus by palpating between the cricoid cartilage and suprasternal notch. An isthmus may not be felt, but if it is, this can help locate the gland. When palpating the lobes, it is beneficial to relax the sternocleidomastoids. To better feel the left lobe, for example, the neck can be slightly flexed and rotated to the left to relax the left sternocleidomastoid and to make space for the palpating fingers or thumb between the sternocleidomastoid and trachea. There are certain additional maneuvers that may be useful, such as measuring neck circumference or the dimensions of a lobe with calipers, but no information is available to assess accuracy or precision of these techniques. Other elements of the thyroid examination that are carried out concomitantly with size assessment include determining gland texture, gland mobility, tenderness, and the presence of nodularity. Auscultation also may be performed for the presence of bruits. These features have their own implications but are not central to determining the presence of a goiter and so are beyond the scope of this discussion. If no thyroid is detected in the neck, it may be maldescended or intrathoracic. Methods of examining for these variants will not be discussed here, because, again, no information is available to analyze the reported techniques.
Dogma holds that the thyroid examination is improved by having the patient swallow during both inspection and palpation. Indeed, it has been stated that swallowing increases sensitivity of inspection alone to that of inspection combined with palpation.28 No study, however, has actually analyzed whether a swallowing maneuver is of benefit, although most examiners believe it is. The movement resulting from swallowing accomplishes several things. First, it changes the shadowing of any mass, enhancing visual detection of a bulge in the neck contour that may be too subtle to be detected otherwise. Second, movement of the thyroid raises a low-placed gland up from below the sternal notch or lower sternocleidomastoid, making it accessible when it may not have been so previously. Third, as in any palpation technique, movement of the object against the palpating hand increases definition. Finally, because only the larynx, upper trachea, and thyroid gland move with swallowing, this maneuver can aid in anatomic localization.29 The degree of excursion of the thyroid on swallowing is proportional to the size of the bolus swallowed, so the patient should be given a sip of water.30
When the thyroid is examined to determine the presence of a goiter, the goal is to estimate gland size. Most endocrinologists express findings in absolute mass or as relative to an upper limit of a normal-sized gland, such as “normal” or “2 to 3 times normal size.” Many nonendocrinologists have some difficulty quantifying thyroid mass, but this ability is crucial in accurately classifying a gland, as will be discussed in the analysis of accuracy.
False-Positive and False-Negative Goiter Results
Finding a goiter when one is not present may simply be an error in detection. There are, however, several common causes of a false-positive goiter or pseudogoiter finding. One is simply an easily palpable gland in a thin individual.5 Because the entire thyroid is so accessible, the tendency is to interpret this accessibility as being due to an enlarged gland rather than the true reason, a decrease in interfering tissues that normally block access to the gland. A second cause is a variant of the normal placement of the thyroid gland in the neck. In some individuals, the gland is higher than usual, and this prominence is again attributed to enlargement.31 A third anatomic variant has been termed Modigliani syndrome.32 In Modigliani syndrome, the thyroid actually lies in a normal position below the cricoid cartilage, but such individuals possess long, curving necks that enhance the prominence and palpability of the gland. A fourth condition producing pseudogoiter is a fat pad in the anterior and lateral portion of the neck.24 Although this condition may be more common in obese individuals, it can also be found in those of normal weight, particularly young women. With experience, examiners can learn to differentiate this from true thyroid tissue by the differing textures and shapes and the lack of movement of a fat pad with swallowing. Another cause involves the thyroid being pushed forward by lesions behind it, making it more easily palpable.5, 33 Finally, any enlargement in the vicinity of the thyroid gland may be mistaken for an enlarged thyroid gland, particularly if it is adherent to the thyroid or larynx and so moves with swallowing.29
There are 3 principal causes of false-negative goiter detection in addition to true misclassification. The first and probably most common cause, of course, is an inadequate physical examination. In some circumstances, an imperfect examination is unavoidable, as when a patient is intubated. In most cases, however, with a little effort, a good examination can be performed on virtually all patients. Second, some individuals, particularly the obese, the elderly, or those with chronic pulmonary disease, have short and thick necks, obscuring the thyroid.5, 24, 34 Some patients also have an atypical thyroid placement, such as a retrosternal location, or lobes that are lateral and obscured by the sternocleidomastoids, making palpation difficult.35
Precision of Estimating Thyroid Size
Data on interobserver precision in estimating thyroid size are available both for rating scales that attempted to place glands in one of 3 or 4 categories according to palpability and visibility and for simple estimation of the presence or absence of a goiter (Table 21-2). Agreements were good to very good in both cases. When glands were placed in categories, κ ranged from 0.47 to 0.74, with a value from combined data of 0.70 (95% confidence interval [CI], 0.68-0.72).7, 8, 36, 37 (The κ statistic and other statistical measures are defined in the introductory article to this series.38) For determination of goiter, κ ranged in these 4 studies from 0.38 to 0.77, with a value for combined data of 0.77 (95% CI, 0.76-0.79). Similar results were reported in another study,39 in which observers determined whether individual lobes were enlarged, with κ from 0.32 to 0.62, and in yet another report40 that determined the presence of a goiter, with κ from 0.10 to 0.54. Because of the nature of the rating scales used in 2 of these studies,8, 37 we can specifically compare interobserver variability for the techniques of inspection (κ = 0.65; 95% CI, 0.62-0.69) and palpation (κ = 0.74; 95% CI, 0.67-0.82). These techniques did not differ significantly in the level of agreement, and both were very good (Table 21-3).
Table 21-2.Interobserver Precision in Assessment of Thyroid Size or Presence of Goiter |Favorite Table|Download (.pdf) Table 21-2. Interobserver Precision in Assessment of Thyroid Size or Presence of Goiter
|Reference ||Agreement ||κ |
| ||All Categoriesa ||Goiter Onlyb ||All Categoriesa ||Goiter Onlyb |
|Trotter et al36c ||0.67 ||0.83 ||0.48 ||0.50 |
|Kilpatrick et al8d ||0.86 ||0.95 ||0.74 ||0.77 |
|Dingle et al37e ||0.85 ||0.87 ||0.47 ||0.38 |
|Trowbridge et al7d ||Not available ||0.96 ||Not available ||0.58 |
|Combined (95% CI) ||0.86f (0.82-0.90) ||0.92 (0.90-0.94) ||0.70f (0.68-0.72) ||0.77(0.76-0.79) |
Table 21-3.Comparison of Interobserver Precision for Thyroid Inspection and Palpation |Favorite Table|Download (.pdf) Table 21-3. Comparison of Interobserver Precision for Thyroid Inspection and Palpation
|Reference ||Agreement ||κ |
| ||Inspection ||Palpation ||Inspection ||Palpation |
|Kilpatrick et al8 ||0.95 ||0.89 ||0.77 ||0.76 |
|Dingle et al37 ||0.87 ||0.89 ||0.38 ||0.60 |
|Combined (95% CI) ||0.93 (0.90-0.96) ||0.89 (0.85-0.92) ||0.65 (0.62-0.69) ||0.74 (0.67-0.82) |
As might be expected, most disagreements between observers involved smaller glands and those near the cutoff for goiter determination, and most disagreed by only 1 stage in classifications.7, 8, 36, 37 Agreement may be better between examiners with greater experience than between those with differing levels of training.40
In 2 studies,6, 22 examiners placed thyroid size in categories of enlargement and repeated the examination on a separate occasion (Table 21-4). These data produced a κ from combined numbers of 0.59 (95% CI, 0.52-0.65) for placement in all categories of the rating scales used by the examiners. For simply determining the presence or absence of goiter, κ ranged from 0.47 to 0.79, with a κ from combined data of 0.65 (95% CI, 0.63-0.67), which is very good. Similar results were reported in a study of patients with various thyroid diseases, in which κ ranged from 0.54 to 0.74.39 Intraobserver agreement was slightly better for the inspection component of the examination (κ = 0.73; 95% CI, 0.71-0.76) than for palpation (κ = 0.65; 95% CI, 0.63-0.67) (Table 21-5).
Table 21-4.Intraobserver Precision in Assessment of Thyroid Size or Presence of Goiter |Favorite Table|Download (.pdf) Table 21-4. Intraobserver Precision in Assessment of Thyroid Size or Presence of Goiter
|Reference ||Agreement ||κ |
| ||All Categoriesa ||Goiter Onlyb ||All Categoriesa ||Goiter Onlyb |
|Hennessy6c ||0.83 ||0.90 ||0.70 ||0.79 |
|MacLennan et al22d ||0.79 ||0.82 ||0.41 ||0.47 |
|Combined (95% CI) ||0.81 (0.77-0.84) ||0.85 (0.82-0.88) ||0.59 (0.52-0.65) ||0.65 (0.63-0.67) |
Table 21-5.Comparison of Intraobserver Precision for Inspection and Palpation |Favorite Table|Download (.pdf) Table 21-5. Comparison of Intraobserver Precision for Inspection and Palpation
|Reference ||Agreement ||κ |
| ||Inspection ||Palpation ||Inspection ||Palpation |
|Hennessy6 ||0.93 ||0.90 ||0.82 ||0.79 |
|MacLennan et al22 ||0.95 ||0.82 ||0.18 ||0.47 |
|Combined (95% CI) ||0.94 (0.92-0.96) ||0.85 (0.82-0.88) ||0.73 (0.71-0.76) ||0.65 (0.63-0.67) |
Accuracy of Estimating Thyroid Size
Three criterion standards have been used in assessing the accuracy of thyroid size determination: weight measured after surgical or postmortem removal, ultrasonographic assessment, and nuclear scintigraphy. Ultrasonographic assessments of thyroid weight correlate well with true gland weight as determined after excision (r = 0.88-1.0), although there is lack of agreement as to the best formula to use for estimating size.18, 21, 41 Nuclear scan determination is a little less reliable but acceptable (r = 0.77-0.98).9, 42, 43 Again, different formulas have been used to translate the scintigraphic profile to thyroid volume.9, 42, 43
Combining data from 9 studies of detection of goiter by physical examination,12, 17, 18, 21, 44, 45, 46, 47, and 48 the sensitivity from combined data was 0.70 (95% CI, 0.68-0.73) with a specificity of 0.82 (95% CI, 0.79-0.85) (Table 21-6). If a goiter was clinically detected, the positive likelihood ratio (LR+) of one being present was 3.8 (95% CI, 3.3-4.5). Conversely, if a goiter was not thought to be clinically present, the negative likelihood ratio was 0.37 (95% CI, 0.33-0.40). These likelihoods are comparable with or better than those for many other physical signs49, 50 and were not affected by the presence of single or multiple nodules.48 Experienced examiners were somewhat more accurate in their assessments than more junior colleagues.48
Table 21-6.Accuracy of the Clinical Assessment for the Presence of a Goitera |Favorite Table|Download (.pdf) Table 21-6. Accuracy of the Clinical Assessment for the Presence of a Goitera
|Reference ||Sensitivity ||Specificity ||LR+ ||LR– |
|Silink and Reisenauer17b ||0.64 ||0.89 ||5.8 ||0.40 |
|Tannahill et al21c ||0.93 ||0.75 ||3.7 ||0.09 |
|Hegedus et al44d ||0.43 ||1.00 ||Infinity ||0.57 |
|Hegedus et al45d ||0.60 ||1.00 ||Infinity ||0.40 |
|Hegedus et al46d ||0.77 ||0.80 ||3.9 ||0.29 |
|Berghout et al18e ||1.00 ||0.62 ||2.6 ||0.00 |
|Perrild et al47f ||0.64 ||1.00 ||Infinity ||0.36 |
|Hintze et al12g ||0.66 ||0.74 ||2.5 ||0.46 |
|Jarlov et al48c ||0.80 ||0.80 ||4.0 ||0.25 |
|Combined (95% CI) ||0.70 (0.68-0.73) ||0.82 (0.79-0.85) ||3.8 (3.3-4.5) ||0.37 (0.33-0.40) |
Some authors have defined specific stages of thyroid enlargement according to the usual sequence of changes that occur as the thyroid gland increases in size. Because some of these staging classifications incorporate observations not normally used in simply estimating thyroid mass, they can significantly enhance the predictive abilities of the clinician (Table 21-7). In the combined data from 4 studies,19, 20, and 21, 48 when a clinician thought that a thyroid gland was of normal size, the LR+ of goiter being present was 0.15 (95% CI, 0.10-0.21). If classified as 1 to 2 times normal size, the LR+ was 1.9 (95% CI, 1.1-3.0), and for greater than 2 times normal, the LR+ was 25 (95% CI, 3.6-175).
Table 21-7.Accuracy in Assessing Grades of Thyroid Gland Weight |Favorite Table|Download (.pdf) Table 21-7. Accuracy in Assessing Grades of Thyroid Gland Weight
|Reference ||LR+ |
|Normal Thyroid Size, 0-20 g |
|Williams et al19a ||0.00 |
|Smith and Wilson20a ||0.00 |
|Tannahill et al21b ||0.10 |
|Jarlov et al48b ||0.26 |
|Combined (95% CI) ||0.15 (0.10-0.21) |
|Thyroid Size 1-2 Times Normal, 20-40 g |
|Williams et al19a ||Infinity |
|Smith and Wilson20a ||0.32 |
|Tannahill et al21b ||2.2 |
|Jarlov et al48b ||2.6 |
|Combined (95% CI) ||1.9 (1.1-3.0) |
|Thyroid Size > 2 Times Normal, >40 g |
|Williams et al19a ||Infinity |
|Smith and Wilson20a ||Infinity |
|Tannahill et al21b ||Infinity |
|Jarlov et al48b ||13 |
|Combined (95% CI) ||25 (3.6-175) |
Certain staging methods for thyroid enlargement can help clarify the true status of some of the patients with glands thought to be 1 to 2 times normal size after routine inspection and palpation.14, 17 The amount of prominence of the thyroid on lateral inspection, for example, resulted in a high likelihood of goiter if it was greater than 2 mm (Table 21-8). Of further utility was finding that a gland was not visible with the neck extended, a result that effectively ruled out a goiter.
Table 21-8.Accuracy in Assessing Thyroid Size by Categories |Favorite Table|Download (.pdf) Table 21-8. Accuracy in Assessing Thyroid Size by Categories
|Stage, Size ||LR+ (95% CI) |
|Method of Silink and Reisenauer17a |
|0, not visible ||0.41 (0.34-0.49) |
|1, 0-2 mm ||3.4 (1.8-6.3) |
|2, 2-10 mm ||Infinity |
|3, >10 mm ||Infinity |
|Method of Berghout et al14b |
|0A ||0.00 |
|0B ||0.00 |
|1 ||1.00 (0.42-2.4) |
|2 ||3.9 (1.8-8.2) |
|3 ||Infinity |
Bias in Estimating Thyroid Size
When the results from 4 studies19, 20, and 21, 48 estimating thyroid gland weights were combined, a regression line was produced describing the bias in gland size determination (Figure 21-3). This clearly shows that sizes of smaller glands are routinely overestimated, whereas those of larger glands are underestimated. The size at which this crossover occurs corresponds to about 2 times normal size. The practical application of this finding is that glands in the 1- to 2-times-normal-size category fall in the range in which size is typically overestimated.
Error in Estimating Thyroid Mass
Error in estimating thyroid mass can be described by the following formula: percentage of error = (–0.656 × mass) + 34.8, where thyroid mass is expressed in grams (r = 0.41; P < .001). The 95% confidence interval is indicated by the broken lines.
To determine whether a goiter is present, follow these steps:
Examine the thyroid gland by inspection and palpation.
Categorize thyroid size as normal or goiter. Subcategorize goiter as small goiter (1-2 times normal) or large goiter (greater than 2 times normal).
If you placed the thyroid in the small-goiter category, consider whether you overestimated the size; determine whether there is any prominence in the profile of the neck in the region of the thyroid when viewed laterally (classify the prominence as ≥2 or >2 mm), and determine whether the gland is not visible from the front with the neck extended.
Place your patient in one of the following categories: “goiter ruled out,” normal thyroid size or thyroid considered to be not visible with neck extended; “goiter ruled in,” large goiter present or lateral prominence greater than 2 mm; or “inconclusive,” all other findings.
Author Affiliations at the Time of the Original Publication
Division of Endocrinology and Metabolism, Department of Medicine, University of Alberta, Edmonton, Alberta, Canada
This work was supported by the Alberta Heritage Foundation for Medical Research.
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