solitry thyroid nodule by FNAC

Investigating Solitary Thyroid Nodule:
1.All solitary thyroid nodule patients should undergo thyroid function tests. In the patient with a solitary hyperfunctioning thyroid nodule, elevated T4– and unrecordable TSH levels confirm the diagnosis of hyperthyroidism.
2.Ultrasonography:
Ultrasonography of the thyroid is best performed using real-time ultrasound equipment with high resolution transducer. Ultrasonography provides highly accurate information on the physical characteristics of a goiter, reliably distinguishing solid nodules from those which are cystic or of mixed echogenecity. Thyroid malignancy is more likely to be present within a nodule which is solid than within one which is cystic. However the occurence of papillary carcinoma within a cystic or partially cystic thyroid nodule is well recognised.
In Kakkilaya Harish's study none of the cystic lesions on ultrasonography were malignant, whereas 5(8.5%) out of 59 cases of solid lesions showed evidence of malignancy on FNAC.
Ultrasonography will also detect the presence of additional, clinically unsuspected nodules within the gland, and may then suggest a diagnosis of multinodular goiter. In one study of patients with solitary thyroid nodules 40% had additional nodules (Scheible et al 1979). It is commonly stated that demonstration of multiple nodules on ultrasound in a patient with a single palpable nodule makes malignancy unlikely. But ultrasound has also detected nodules in 30% of asymptomatic adults, and no carefully controlled study supports this contention. and the malignant potential of any nodule should be based on other criteria. Hence single dominant nodule palpated needs to be proved benign as around 5-10% of them are malignant.
In Kakkilaya Harish's study, ultrasonography showed evidence of accessory nodules, which were clinically not palpable in 33% of cases and out of these, all were benign except for one which showed indeterminate cytology on FNAC.
There is general agreement that there are no reliable sonographic criteria which permit distinction between benign and malignant thyroid swelling. Extension of tumour out of the thyroid into adjacent tissues or associated lymphadenopathy may suggest the diagnosis of thyroid cancer but does not prove it.
Ultrasonography may be used to monitor the size of solitary thyroid nodules, especially in those patients who are on thyroxine suppressive therapy.
In a review of published series of ultrasound scans 69% of nodules were found to be solid, 19% cystic and 12% mixed. Of cases proceeding to surgery 21% of the solid lesions were found to be malignant, compared with 7% of the cystic lesions (Ashcraft & Van Hurle, 1981).
In a study by Kakkilaya Harish out of true solitary thyroid nodules on ultrasonography 59 (88%) were solid and 18 (12%) were cystic. None of the cystic lesions were malignant on FNAC , where as 5(8.5%) out of 59 cases of solid lesions showed evidence of malignancy and 7 (11.9%) showed evidence of indeterminate cytology . All the 5 histologically proved malignancy in our study were solid lesions on ultrasonography.
As the ultrasonography can not differentiate between benign and malignant lesions and although ultrasonography can demonstrate subclinical nodularity and cyst formation, the former is clinically irrelevant and the latter apparent at FNAC, which is used routinely on all patients, the routine use of ultrasonography has been largely abandoned.
3.Thyroid Scintigraphy:
Thyroid scintigraphy allows us to analyse thyroid tissue pictorially. Scintigraphy can determine whether cervical masses contain thyroid tissue, it can differentiate solitary thyroid nodule from multinodular goitre, it can show the functional status of the nodule, and it can demonstrate whether metastasis from thyroid cancer concentrate iodine and could be amenable to treatment with radioiodine.
The two commonly used radio-pharmaceuticals for standard imaging are iodine ¬ 123I and technetium ¬ 99 pertechnetate (99mTC). 131I is used for whole body imaging in patients who have differentiated thyroid cancer.
The shorter half life of 123I (13 hrs) as compared to 131I (8 days) and the absence of beta emission explains the relatively low radiation dose to the thyroid by 123I compared with 131I. Hence 123I preferred over 131I for diagnostic purposes.
Now most laboratories use 99mTc, due to its easy availability, its low radiation dose to thyroid (half life 6 hrs) and its economic advantage . The pertechnetate ion (TcO4) is trapped by the thyroid iodide concentrating mechanism but normally is not incorporated into organic form. 123I has the advantage of being a radionuclide of iodine and is therefore more physiologic. 123I is trapped and organified by the thyroid tissue. The usual dose is 200 microCi. to 400 microCi by mouth or intravenous route. The 13 hour half life makes it suitable for imaging upto 24 hrs using the gamma camera. 131I is used for whole body scintigraphy in patients who have proved differentiated thyroid cancer that has been removed surgically to identify metastases or remnants in the neck.
L-thyroxine must be stopped at least 4 weeks and L-tri-iodothyronine (T3) for 10 to 14 days before imaging.
In normal subjects, the lobes of the thyroid gland appear as pear shaped homogenous structures on scintiscan, the isthmus is often not seen.
Scintigraphy provides a functional assessment of the thyroid, so that a single nodule may demonstrate diminished or absent uptake, equal concentration or increased uptake of isotope when compared to the normal surrounding thyroid tissue, respectively categorized as cold, warm and hot nodule.

Hot nodule in left lobe

Cold nodule in left lobe
Ashcraft and Van Herle reviewed published reports and compared 123I scan with histopathology findings. A cold nodule was present in 84%, hot nodule in 5% and warm nodule in 9% of patients who underwent scanning. Of the cold nodules 16% were malignant and 4% of the hot nodule and 9% of warm nodules were also malignant.
Ashcraft and Van Herle also reviewed the result of 99mTc scintigraphy. 72% patients had cold nodules, 19% had warm nodules and 9% had hot nodules. Malignancy was found in 22% of cold nodules, 13% of warm nodules and 29% of hot nodules.
In a study by Kakkilaya Harish, all patients underwent 99mTc Scan and 82% were cold nodules, 6% warm nodules and 12% were hot nodules. On FNAC malignancy was found in 3.7% of cold nodules, 33.6% of warm nodules and in none of hot nodules. Out of 39 cold nodules who underwent surgery 4 (10.25%) were malignant on histological examination and one (20%) out of 5 warm nodules was malignant, none of 3 hot nodules were malignant.
From these findings it is evident that 99mTc scintiscan is not valuable in increasing or decreasing the likelihood of cancer.
There are numerous reports of a nodule showing disparate scintigraphic appearances on 123I and 99mTc scintiscan. This discrepancy can be explained by the fact that radioiodine is trapped and organified, where as 99mTc is only trapped. The more frequent discrepancy is one in which the nodule appears hot on 99mTc scan but cold on 123I scan. A significant proportion of nodules showing this pattern are cancers. Due to the increased vascularity in malignancy it will be hot on 99mTc scan, but due to lack of functioning tissue it will be cold on 123I scan.So it is recommended that a nodule that appears hot on 99mTc scintiscan should undergo repeated imaging with 123I.
To conclude, no criteria have been identified to differentiate benign from malignant thyroid nodules on the basis of scintiscan. However some conclusions relating to the relative rise of a solitary thyroid nodule being malignant can be drawn from the isotope scan result. First, the vast majority of cancers arise in hypofunctioning or cold thyroid nodules. The possibility of malignancy occurring within a hot nodule is low. Although thyroid carcinomas are 'cold' on isotope scanning, they constitute only a small proportion (14-22%) of cold nodules. Thus on thyroid isotope scan, sensitivity for diagnosing cancer is high but specificity is unacceptably low.
As the cold thyroid nodule poses a concern for malignancy, the 'hot' thyroid nodule usually evokes the possibility of hyperthyroidism. Among patients with hot thyroid nodules 80% are euthyroid and 20% are thyrotoxic. Hot nodule may turn out to be autonomously functioning thyroid nodule. Autonomous thyroid nodule is characterised by growth, iodine uptake and function all independent from TSH control.
As stated earlier a 'hot' nodule on 99mTc scan can turn out to be 'cold' on 123I scan. So a "true" hot nodule is one which shows hyperfunction with 123I and 99mTc scan as well. To diagnose autonomously functioning nodule, the patient should be given 25 microgram of T3 three times daily for 7 to 10 days and the scintiscan repeated. If the repeat scan shows uptake the nodule is considered autonomous.
Due to the absence of reliable discriminatory criteria for benign and malignant lesions, the routine isotope scanning in the investigation of the patient with a solitary thyroid nodule has been discontinued by many authors.
Isotope scanning is now only indicated when toxicity is associated with nodularity, when FNAC shows evidence of follicular neoplasm and when retrosternal goitre is suspected.
4.Fine Needle Aspiration Cytology :
The technique of fine needle apsiration (FNAC) of goitre for cytological assessment was pioneered in Sweden and is now used increasingly as a first line investigation of the patient with solitary thyroid nodule. The attractions of FNAC are that it is easily performed with inexpensive equipment in the out patient department, it is essentially free of complications, and above all it provides a reliable and accurate tissue diagnosis in a high proportion of patients.
The technique of FNAC is relatively straight forward and free of significant complications and the concern that
percutaneous insertion of a needle into a malignant lesion might lead to dissemination and to seeding of the needle tract with malignant cells has been allayed.
Cytodiagnosis will designate a lesion as benign, malignant or indeterminate . A benign cytodiagnosis refers to smears containing abundant colloid and typical follicular cells (colloid adenoma) or displaying features of thyroiditis. The malignant category is composed of smears displaying features indicative of papillary carcinoma or less commonly of follicular carcinoma, medullary carcinoma, anaplastic carcinoma, lymphoma or metastases. An indeterminate cytodiagnosis refers to smears containing little colloid and many follicular cells or Hurthle cells in a pattern suggestive of a neoplasm. Most experts agree that it is extremely difficult, if not impossible to discriminate between benign follicular adenoma and follicular carcinoma on cytological appearance alone. Confirmation of a diagnosis of follicular carcinoma is dependent upon the visualisation of capsular and/or vascular invasion by the tumour, following careful serial sectioning and histological examination of the lesion. Although the cancer rate within this indeterminate group of tumours is only approximately 20%, it remains policy of all experts to advise surgical resection of all such lesions (Lowhagen et al 1979)
CYTODIAGNOSTIC CATEGORIES OF FNAC
• Benign
• Macrofollicular (colloid) Adenoma (Adenomatous nodule)
• Thyroiditis
• Cyst
• Malignant :
Papillary, Follicular
Medullary, Anaplastic
Lymphoma
Metastases
• Indeterminate:
Microfollicular, Hurthle cell or Embryonal neoplasm.
Although FNAC is a relatively simple and low cost procedure, if it is to serve as a truly reliable diagnostic tool, the predictive value of a clearly benign (negative) cytodiagnosis should approach 100%, indicating a virtual zero probability of malignant disease being present (Negative predictive value). A number of studies have sought to evaluate this issue by comparing the pre-operative cytodiagnosis with the subsequent histopathologic diagnosis in patients who underwent surgical excision of the nodule. The results of several such studies published since 1990 from which such data could be extracted are summarised and reviewed by Woeber A. K. In his review the negative predictive value of a benign cytodiagnosis ranges between 89% and 98% in the seven studies with a mean of 94% or a false negative rate of 6%. The negative predictive value of an indeterminate cytodiagnosis was much lower, the false negative rate averaging 27%. In this study the false positive rate of malignant cytodiagnosis was only 4%. Thus the overall diagnostic accuracy of FNAC for benign and malignant lesions in these studies were 95%.
In a study by Kakkilaya Harish the negative predictive value of a benign cytodiagnosis was 97.14% or a false negative rate of 2.86%. The negative predictive value of indeterminate cytology was 75%, the false negative rate being 25% .The false positive rate of malignant cytodiagnosis was 50%. The over all diagnostic accuracy of FNAC for both benign and malignant lesions in that study was 92.3%. The diagnostic specificity of FNAC was 94.4% but sensitivity was only 66%
Despite its limitations, there can no longer be any doubt that FNAC now represents the prime investigation in the
assessment of the patient with a solitary thyroid nodule, and should by employed routinely (Rosen et al 1981). FNAC is capable of providing critical information which is unobtainable by any other investigation short of surgical resection. A definitive tissue diagnosis permits the option of non operative management of the patient with benign disease and will allow planning of an appropriate surgical strategy when thyroid carcinoma is demonstrated. The identification of anaplastic carcinoma or thyroid lymphoma frequently obviates the requirement for unnecessary surgical exploration for lesions that are usually best treated by non surgical means. The use of fine needle aspiration biopsy had halved the number of patients with solitary thyroid nodules undergoing surgery and has increased the proportion of cancers amongst those undergoing thyroidectomy (Hamberger et al 1982).
Finally, not only has the availability of FNAC virtually eliminated the requirement for isotope scanning and ultrasonography, but as a significant number of patients are now treated without operation, feeling secure in the knowledge that their goitres are benign, there are substantial financial savings.
5. Core needle biopsy, employing a needle of the Tru-Cut type and carried out under local anesthetic, is occasionally of value in establishing a diagnosis. Core biopsy produces a small cylinder of tissue which is then submitted to histological, not cytologicaì examination. Because of the calibre of the needle and the consequent risk of haemorrhage and injury to adjacent structures, there is no place for large needle biopsy of this type in the routine assessment of the solitary thyroid nodule.
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Management of solitary nodule
Multinodular goitre
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What is a thyroid nodule?
A thyroid nodule is a swelling that develops in the thyroid gland. It can be due to growth of thyroid cells or a collection of fluid known as a cyst. Thyroid nodules are relatively common. They can be felt in approximately 6% of woman and 2% of men. Sensitive testing by ultrasound can reveal small nodules in as many as one third of all adults.

Thyroid nodules can cause trouble for patients in three ways.

1) They can become large enough to press on nearby structures in the neck, such as the swallowing tube (esophagus) and windpipe (trachea)

2) They can overproduce thyroid hormone (hyperthyroidism)

3) They can be cancer

Most thyroid nodules are benign growths that may increase in size but do not spread beyond the thyroid gland. About 5% of nodules turn out to be malignant growths representing cancers that can spread beyond the thyroid gland to other parts of the neck and other areas of the body. One of the most important questions that should be answered when a thyroid nodule is identified is whether it may represent a form of thyroid cancer.




How are thyroid nodules discovered?
If a thyroid nodule grows to a large enough size, a patient or an observer may first notice it as a new lump that appears in the lower front part of the neck. Most thyroid nodules are located just to the right or left of the midline of the neck. If a lump in the lower front part of the neck moves up and down with swallowing, it is likely to be a thyroid nodule.

Thyroid nodules may also be found during routine physical examinations. To confirm that a lump is located in the thyroid gland, it is often necessary to perform special physical examination maneuvers. This usually involves having the patient swallow while the examiner watches and feels the thyroid gland.

When radiographic studies (e.g., ultrasound, CT, and MRI) are used to evaluate other conditions involving the head and neck, thyroid nodules can be incidentally discovered. These thyroid nodules tend to be smaller than those that are detected by patients and examiners. The size of such incidentally discovered thyroid nodules helps determine whether they should be investigated more thoroughly as suspicious growths.

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