Diagnosis And Surgical Treatment Of Papillary Thyroid Microcarcinoma(PTMC): A Report Of 42 Cases

1. BackgroundPapillary thyroid microcarcinoma (PTMC) is a specific subgroup of papillarythyroid carcinoma (PTC) based on the size of the primary tumors of 1.0 cm or less indiameter. PTMC has been defined strictly by size criteria. Although some authors haveincluded lesions that measure 1.5 cm in greatest diameter, the World HealthOrganization and most diag- nostic pathologists adhere to the definition of a tumormeasuring 1 cm or less.At present, PTMC is defined as"incidental"when discovered at histologicanalysis of a thyroid gland removed for a preoperative diagnosed benigndisease. Instead, PTMC is defined as"occult"when it is undetectable at clinicalexamination and indirectly diagnosed because of the presence of enlarged metastaticcervical lymph nodes or distant metastases, and then discovered at surgery. The term ofthe description of clinically undetectable thyroid cancer has evolved overtime. Initially, the term"latent aberrant thyroid"was used to indicate the presence ofthyroid tissue in cervical lymph nodes of subjects with a clinically normal thyroidgland. These lymph nodal thyroid tissue foci were found eventually to be metastaticpapillary thyroid carcinoma spreading from clinically undetectable intrathyroidlesions smaller than 1.5 cm.To this reason, the term "lateral aberrant thyroid" wasdiscarded. This term has been replaced by the term "occult papillary carcinoma"todescribe a focus of papillary thyroid cancer measuring less than 1-1.5cm. The term"occult"carcinoma, however, is not recommended because it does not describe thetumors pathologically or clinically; In fact in the era of ultrasonography, the term hasbecome meaningless and has appropriately fallen into disuse. Moreover, in recentyears, the improved spatial resolution of US and the use of FNAC (frequently usedunder US guidance) have strongly favoured the preoperative diagnosis of very smallpapillary thyroid carcinomas undetectable at clinical examination and measuring lessthan 10mm in maximum diameter.These observations have been receipted by theWHO classification of thyroid tumours, in which PTMC is defined as "a papillarycarcinoma sized 10mm or less in its maximal diameter". Thyroid microcarcinoma(TMC)accounts for approximately 6-35% of thyroidcancers. The incidence of PTMC has been reported with different frequencies and inautopsy series, some studies have reported it can be identified in up to 36% of thyroidsin adult patients who died of nonendocrinerelated causes. In surgical series, theincidence of PTMC found incidentally in a lobe or gland removed for benign disease(nodular goiter, follicular adenoma) is reported to be approximately 24%. Thus, fromthis autopsy and surgical data, it is fair to estimate that about one-third of adultsharbor 1 PTMC in their thyroids.Most PTMC show benign behaviour and a high likelihood of remaining silentthroughout a patient's life. They are believed to be a less aggressive subset of papillarycancers that behave more like benign lesions and are often more conservativelytreated(partial thyroidectomy only). However, the fact that not all PTMC remainclinically occult has been recognized. It is worth noting that, in some studies,loco-regional recurrences have been reported in up to 20% of PTMC patients, andseveral cases of distant metastases with fatal outcome have been described.Approximately 10% of PTMC exhibited progressive clinical courses, while less than1% resulted in mortality. For these reasons, some authors favor aggressive surgicalresection and adjunctive therapy(total thyroidectomy followed by radioiodinetherapy).The widespread use of highresolution thyroid ultrasonography has led to therecognition that a large number of healthy subjects have thyroid smallnodules. Different recommendations on how thyroid small nodule patients should bemanaged still remains a subject of debate amongst surgeons. Therefore, tocharacterize the clinical diagnosis and optimal surgical management for PTMC, ourclinical data of PTMC were analyzed retrospectively.2. ObjectiveThe objective of this thesis was to study the experience in the diagnosis andsurgical management of PTMC and elevate the level on diagnosis and treatment ofPTMC.3. Methods and resultsFrom January 1996 to January 2007, 42 patients with PTMC underwent thyroidsurgery in the Second Hospital of Tianjin Medical University and relative materials were retrospectively analyzed.Eight male and 34 female patients, a media age of 42 years (range:16-63 years),were operated and diagnosis were confirmed by pathological exam.The mean tumorsize was 0.73±0.19cm(0.3-1cm) in diameter.Thirty-four of 42 patients(80.9%) withclinical unpalpable thyroid small nodules were detected by high resolution thyroidultrasonography preoperatively.None of the patients with PTMC was identified onpreoperative by fine-needle aspiration cytology; Nineteen patients of 42 underwentfrozen sections and 14 of these(73.7%)diagnosis were confirmed during operation.Twenty-eight patients(66.7%),the diagnosid were made in the final histopathologicalexamination. The media follow-up duration of these patients was 5.5 years. Of the 42patients,30 (71.4%)underwent a lobectomy and,11 of 30 patients supplemented levelⅥdissection. None of these patients had recurrence during this period. Therecurrence of three patients with multifocal and underwent incompleteresection(partial thyroidectomy)were observed at follow-up.Disease-relate mortalitywas not observed.4. Conelusions1. PTMC are often occult and dificullt to be diagnosed preoperately.Most of them inclinical un-palpable may be detected by high resolution thyroid ultra-sonographphyand were diagnosed by frozen section during the operation.2. Surgery isthe most important treatment of PTMC. The Lobectomy supple-mentedlevelⅥdissection was safe for the patients with PTMC at the stage of cNO.