Pattern of thyroid diseases in central Sudan: (cid:16) uclear medicine perspective.

: Thyroid scintigraphy using Tc-99m pertechnetate is a frequently performed procedure in routine nuclear medicine practice in addition to thyroid hormonal assay by radioimmunoassay (RIA). There is no clear description of thyroid diseases pattern in Sudan using nuclear medicine as a diagnostic tool. The aim of this retrospective study is to determine the pattern of thyroid diseases using the nuclear medicine facilities in our institute during a period (2001-2003). Methods: All patients referred to the department of nuclear medicine for thyroid scan from January 2001 to December 2003 were included in this study and the thyroid function test when available. Data were analyzed by SPSS software. Results: A total of 2070 patients were referred to the department and only 1605 (77.5%) have thyroid function test results available for scan reporting. Female to male ratio is 9:1. The mean age is 34 ±13.36 (1-86 years old). The most common pattern is simple multinodular goiter 784 (37.8%) and the second is solitary thyroid nodule 506 (24.4%), followed by simple diffuse goiter 415 (20%). From a total of 1605 thyroid function test results, 1377 patients (85.8%) were euthyroid, 168 (10.5%) were having hyperthyroidism while only 60 (3.7%) were having hypothyroidism. Conclusion: The vast majority of patients in this study were young females with simple goiter and normal radionuclide uptake. No more information gained particularly when the patient is known clinically and biochemically to have a simple goiter. A solitary cold nodule is also common.

uclear medicine plays a crucial role in the diagnosis of thyroid diseases. Thyroid hormonal assay by radioimmunoassay (RIA) and thyroid scan and uptake, are the principal nuclear tests in thyroid disease. Thyroid scintigraphy using Tc-99m pertechnetate is a frequently performed procedure in routine nuclear medicine practice. For most patients with thyroid disease, the combination of careful history, skilled physical examination, tests of thyroid function, fine needle aspiration 1-MSc Nuclear Medicine 2-MD Molecular Biology. 3-Fc Rad Onc. 4-FRCR, MSc Nuclear medicine. *National Cancer Institute, University of Gezira. Correspondence E-mail: ahmedelmadani@yahoo.com biopsy, and scintigraphy provide the most cost-effective means of evaluating the thyroid gland and its diseases 1 . Measurement of urine iodine concentration gives insight into iodine intake and can be used to prove iodine deficiency as a cause of goiter. A suppressed serum TSH concentration is the earliest biochemical manifestation of hyperthyroidism 2 . The primary indication for a scan in the case of euthyroid nodular goiter with a low or suppressed TSH level, when autonomous toxic nodule is suspected 3 . Autonomously functioning thyroid nodules appear "hot" on scintigraphy because they selectively concentrate radionuclide to a greater extent than the remaining thyroid gland, which is controlled by the normal T4-TSH feedback mechanism. Thyroid scanning will not distinguish between benign and malignant thyroid lesions 4-6 ]. Any lesion suspicious of malignancy on cytologic examination (by FNAC) may be surgically removed 4 ]. Thyroid scan and uptake may be used to differentiate between different causes of hyperthyroidism. Scintigraphic characteristics also help differentiate between nodular and Graves' disease. Scintigraphy combined with ultrasound examination may be used to identify the underline cause of congenital hypothyroidism such as thyroid agenesis, dyshormonogenesis, and incomplete thyroid descent 7 . Moreover, ultrasound distinguishes cystic form solid thyroid cold nodule, The scintigraphic findings in Hashimoto's thyroiditis are highly variable and can mimic any thyroid abnormality and most of its pattern is diffusely enlarged thyroid gland similar to toxic diffuse goiter 8 . Less common forms of thyroiditis include Riedel's struma, which is characterized by extensive fibrosis of the thyroid gland, and acute suppurative thyroiditis, which is a bacterial infection 9 . Thyroid scan can determine the retrosternal extension of a huge goiter. The cervicothoracic CT-scan is the key examination for the assessment of a retrosternal goitre making it possible to appreciate its features, anatomic relations and tracheal involvement 10 .

Material and Methods:
Nuclear medicine department in the national cancer Institute was established in 1994 and equipped with two gamma cameras (single and dual head) serving all patients in the Gezira state and nearby states and it's the second center in Sudan after radioisotope center in Khartoum (RICK). All patients referred to the department for thyroid scan from January 2001 to December 2003 were included in this study, correlated with thyroid function tests when available. The scintigraphies were all obtained with a 5mm single-hole collimator-equipped gammascintillation camera 10-20 minutes after intravenous injection of 37-111MBq of sodium pertechnetate Tc 99m.
Data were acquired with a 128 x 128 matrix and a zoom factor of 2.67-4.0. Imaging acquisition was terminated at 100 k counts or after 900 s of imaging, whichever occurred first. Radionuclide uptake by the thyroid gland at 10-20 min was also calculated as a percentage of the dose injected, allowing for decay and correcting for background. The normal range of radionuclide uptake applied was 0.5-5%. Diffuse toxic goiter (Graves' disease) was diagnosed in a diffusely enlarged thyroid gland with a high uptake of tracer throughout in correlation with thyroid function test. Viral thyroiditis was diagnosed on the bases of thyroid function tests with short interval signs and symptoms compatible with thyrotoxicosis and the scan showing an inhomogeneous distribution of tracer throughout the thyroid with reduced tracer uptake. Autonomously functioning thyroid nodules show focal areas of increased uptake, with suppressed uptake in the rest of the gland. Nodularity was detected as areas of reduced and nonhomogeneous in tracer uptake. Descriptive analysis of the patients' data was done by SPSS statistical package to determine the thyroid diseases pattern in our region.

Discussion:
The first step in evaluating a patient with suspected thyroid disease is to correlate the normal or abnormal scintigraphic pattern with available biochemical data, clinical history, and physical examination 11 .  19 . In this study, 60.5% of patients were either simple goiter or normal and no additional information gained and hence the management will not change on the bases of the thyroid scan result. Preoperative thyroid isotope scan would influence the operative procedure and the preoperative management in patients with nontoxic goiter only if it raises suspicion of malignancy. However, the scintigraphy shows significantly lower sensitivity and specificity in the detection and prediction of malignant nodules in the thyroid gland 20 . The study revealed that one forth of patients has solitary thyroid nodule and for all of them we suggested fine needle aspiration cytology to rule out the possibility of malignancy (as shown in Fig 2 E). Although physical examination, thyroid scan, fine-needle aspiration biopsy and measurement of serum thyroglobulin are helpful in the management of solitary thyroid nodule, fine-needle biopsy remains the best single cost effective method. When cytologic examination shows malignancy or unspecified neoplasm, surgery is indicated. For most patients with cytologically benign lesions, careful followup will suffice 21 . Ultrasound proved to be especially valuable for differentiating between solid and cystic nodules. This is of practical importance because completely cystic nodules are nearly always benign and may be treated by thin needle puncture with aspiration of the cyst fluid. Differentiating between benign and malignant solid nodules was not possible with ultrasound, however 22 . In addition, ultrasonically guided percutaneous fine needle biopsy is employed for emptying cysts or gaining material for cytological examination 23 . Hence adding ultrasound to the fine needle aspiration cytology (FNAC) technique will improve its specificity, accuracy and positive predictive value.

Conclusion:
The vast majority of patients in this study were young females with simple goiter and normal radionuclide uptake. No more information gained particularly when the patient is known clinically and biochemically to have a simple goiter. A solitary cold nodule is also common pattern. Thyroid scan should not be requested as a routine for very patients with thyroid disease for two reasons: the radiation hazards and the cost.