Coexisting Papillary Thyroid Carcinoma and Hashimoto Thyroiditis in Thyroid Fna, with Associated Genomic Predisposition
Authors: Chantziantoniou Nikolaos 
Published: July 2019

Fine needle aspiration (FNA) biopsy is an established procedure by which to sample thyroid nodules to ascertain etiology and produce a diagnosis conveying risk of malignancy with recommended patient follow-up. This procedure is well-tolerated and endorsed given the accessibility and vascularity of the thyroid gland. FNA cytopathology has proven efficacious for the primary assessment of thyroid nodules. Well-differentiated papillary thyroid carcinoma (PTC) and benign lymphocytic (Hashimoto) thyroiditis (HT) are distinct thyroid lesions that may be reported with diagnostic confidence based on their characteristic cytomorphologic features. However depending on the adequacy of FNA sampling and the morphology of aspirated cellular material, thyroid nodules with coexisting PTC and HT may pose diagnostic pitfalls. This may be dependent upon: (a) the architectural nature of the coexisting lesions in-vivo; (b) whether both lesions are adequately sampled through FNA; and (c) which of the cell types and cytomorphologic features appear in predominance to support interpretation. Such cases may prove diagnostically challenging in adult patient assessments particularly in the setting of hypothyroidism which may also include multi-focal hyperplastic nodularity. Likewise, diagnostic problems may arise in the pediatric setting as thyroid nodules are relatively rare; marked lymphocytic pleomorphism and anisonucleosis may raise concern of lymphoproliferative malignancy; and as intra-thyroid lymphadenopathy can occur. This two-lesion entity is therefore impactful in both the adult and pediatric thyroid FNA practice. This report aims to raise awareness of this entity through a case of thyroid FNA in a 27 year old female, with ultrasonographic, cytopathologic and histopathologic findings. We conducted an English language literature review to explore the experience pertaining to the coexistence of PTC and HT as identified through FNA of the thyroid, and reviewed clinical, prognostic and ancillary testing data that may facilitate diagnosis. Incidentally, as the Sidra Medical and Research Center in Doha, Qatar, is a comprehensive woman's and pediatric hospital, we also investigated the published pediatric experience in correlation with this case. Thyroid FNA Case/

Materials and Methods

The cytopathology service (at King Abdulaziz Medical City Hospital, Riyadh, Saudi Arabia) assisted in an ultrasound-guided thyroid FNA procedure on a 27-year old female presenting with isthmus and bilateral lobe nodules to rule out malignancy. She had no remarkable medical history or previous thyroid disease. Image-guided FNA was performed using 22-gauge stylet needles without syringes attached. Under ultrasound guidance, the needle was advanced as close as possible to the nodule (with the stylet engaged) then the stylet was removed and the needle advanced then into nodule. The passes were performed in different directions inside the nodule. Two needle passes were performed on the right thyroid and isthmus nodules, but three passes were performed on the left thyroid nodule. Aspirated material from each pass was promptly and carefully smeared between two glass slides whereby, with mirror-image smearing, one slide was fixed in 95% ethanol for Papanicolaou staining, and the second slide remained air-dried for Diff-Quik staining. All needles were rinsed with saline, but no cell blocks were prepared due to insufficient needle rinse material. Ultrasonographic Findings: No nuclear medicine studies were performed prior to the thyroid FNA procedure for this patient. Thyroid, isthmus (Fig. 1): Transverse gray-scale ultrasound showed a predominantly solid, well-defined, non-calcified nodule with heterogeneous echo-texture, measuring 1.2 ×  1.8 cm in diameter. Thyroid, right lobe (Fig. 2): Transverse gray-scale ultrasound showed a predominantly solid nodule with ill-defined margins located in the lateral aspect of the mid right thyroid lobe, with heterogeneous echo-texture, measuring 1.0 ×  0.45 cm in diameter. Thyroid, left lobe (Fig. 3): Transverse color Doppler ultrasound showed an ill-defined, non-calcified hypo-echoic avascular nodule measuring 0.6 ×  0.6 cm in diameter. Fine Needle Aspiration Microscopic and Diagnostic Findings: All smears revealed an adequate cellularity of follicular cells. Upon low power microscopic analysis, the smears from the left and right nodules revealed scattered small clusters of benign follicular cells and isolated Hurthle cells in backgrounds of predominating polymorphous lymphocytes. However, the smears from the isthmus nodule included scattered variably-sized clusters/groups of disorganized abnormal follicular cells with pseudo-papillary architecture, marked cellular crowding and depth of focus, against a background of predominating lymphoid cells of various levels of maturity including immature and mature forms, scattered plasma cells, scattered robust Hurthle cells with abundant fragmented eosinophilic cytoplasm, erythrocytes, and proteinaceous/cellular debris with clotting artifact (Figures 4, 5 and 6). With high power microscopy, these follicular cells showed abnormal nuclear features with moderate anisonucleosis: round/oval shapes, irregular envelope contours, evenly-dispersed coarse chromatin clumping, and moderate hyperchromasia, but without marked nuclear envelope wrinkling. Intranuclear invaginations and grooves were rare (Fig. 7). Follicular cell cytoplasm was moderately-abundant and micro-vacuolated, with a blue-grey staining reaction through Diff-Quik staining and basophilic with Papanicolaou staining (Figures 6, 7 and 8). Fragments of connective tissue were also noted intermixed amongst the abnormal follicular cells, as were rare, intact, micro-follicles (Fig. 8 and 9). Deposits of thick colloid were scattered with thin colloid being scarce (Fig. 10). Based on these microscopic findings, cytopathology interpreted the left and right thyroid nodules as being consistent with lymphocytic (Hashimoto) thyroiditis, Bethesda Reporting Category II. The isthmus nodule was interpreted as being suspicious for papillary thyroid carcinoma associated with lymphocytic (Hashimoto) thyroiditis, Bethesda Reporting Category V. Lesion coexistence was suspected. The ensuing recommendation referred to the algorithm as published through the Bethesda reporting system, being that of thyroidectomy. Histopathologic Findings: Total thyroidectomy was performed. Tissue sections from the thyroid isthmus nodule revealed PTC, while the non-neoplastic thyroid tissues showed HT with multi-focal hyperplasia (particularly in the right lobe). Neither definite extrathyroidal tumor extension nor lymphovascular invasion was noted; but deposits of metastatic carcinoma were identified in 5 of 14 dissected lymph nodes. Surgical biopsy confirmed the coexistence of PTC and HT in the isthmus nodule; demonstrating two distinct, characteristic lesions resting adjacently separated by bands of connective tissue (Figs. 11, 12 and 13). Notation: Post-surgery nuclear I131 scanning showed complete ablation of the thyroid tumor.

Conclusions

The HT cytomorphologic template includes polymorphous lymphocytes, plasma cells, robust Hurthle cells, and follicular cells that may occasional have intranuclear invaginations and grooves. In this case, FNA cytopathology conveyed diagnoses of lymphocytic (Hashimoto) thyroiditis for the left, right and isthmus nodules sampled based on the characteristic cytomorphology noted in the smears. The isthmus nodule diagnosis also emphasized suspected coexistence of well-differentiated PTC mainly based on the scattered groups of atypical follicular cells with abnormal nuclear shapes and sizes, chromatin features, and pseudo-papillary 3D architecture with depth of focus. We favored a conservative diagnosis for PTC bearing in mind the following considerations: the possible inflammatory effects of florid HT upon epithelial cells; the possibility of diffuse nodular follicular hyperplasia; and the rarity of intranuclear invaginations and grooves observed. The overall cytomorphologic findings in the smears from the isthmus nodule closely resembled the histologic patterns of well-defined PTC and HT separated by connective tissue. Multi-focal follicular hyperplasia was also identified in the left, right and isthmus thyroid nodules in this case. The lesions were coexisting but physically isolated, and the ultrasonographic detection of heterogeneous echo-texture may reflect this phenomenon. This case emphasizes the importance of adequate FNA technique to ensure the various aspects of thyroid nodules are sampled and proportionally represented through FNA processing and, particularly, for nodules with heterogeneity upon imaging. Also, screening, interpretive and cytopreparatory expertise with optimal fixation and staining are equally critical. HT is also termed chronic lymphocytic or autoimmune thyroiditis, first described by Hakaru Hashimoto. HT is believed to result from a combination of genetic susceptibilities and environmental factors. It is estimated that HT occurs 10–15 times more frequently in women compared to men, with a global incidence of approximately 0.3–1.5 cases per 1,000 individuals. HT is associated with circulating antibodies to thyroid antigens and hypothyroidism due to follicular cell depletion secondary to the effects of chronic inflammation. The possible association between HT and well-differentiated PTC has been described since 1955. Women with HT and any solitary ‘cold’ thyroid nodule upon radio-nuclear scanning should receive ultrasound-guided FNA due to the increased risk of coexisting thyroid cancer. Meta-analyses demonstrate a near three fold risk for patients with HT to also harbor PTC relative to patients without HT. Epidemiologic studies suggest that the detection of PTC in patients with histologically confirmed HT may reach 39%, and that in the presence of HT, the outcome and prognosis of PTC is more favorable relative to patients with PTC only. These data have been used to suggest a ‘protective’ phenomenon resulting from autoimmune targeting of follicular epithelial cells. However the increased risk of tumor suggests that the proliferative changes of the thyroid epithelium are a risk for tumor development, although this may have a better prognosis, again possibly due to local growth factors in the regenerating thyroid. This also suggests HT is a promotor of tumors rather than being protective, though the tumors that develop are less aggressive. An alternative hypothesis is that the developing tumor promotes or initiates an inflammatory response. Tumor infiltrating lymphocytes and immunity are very topical with numerous recent reviews in a wide range of tumors, but in this case it is curious that the tumor showed considerably fewer lymphocytes than the background thyroid as if the tumor expressed fewer immune targets to the lymphocytes and showing some immune avoidance. The role of the immune system and thyroid cancer is complex. The prevalence of coexisting HT and PTC varies globally and this is thought to reflect ethnic, geographic and cytopathologic reporting differences. However, the sensitivity of FNA to detect PTC in patients with HT exceeds 90%. FNA of thyroid in the pediatric population may prove challenging depending on the nature of the lesions sampled, the likelihood of excessive hemorrhage and the possible need for patient sedation. Thyroid nodules in childhood and adolescence are relatively rare: prevalence varies between 0.2–1.44%, and are 5–10 times less common than in adults. However, the mean malignancy risk in pediatric patients with thyroid nodules exceeds 26% with over 90% of cancers being the PTC type. Therefore any thyroid nodule discovered in this age group ought to be investigated with a high degree of suspicion and an aggressive FNA approach. The prevalence of HT in childhood is estimated to be 1.3–9.6%; whereas the prevalence of HT with PTC ranges between 1–30% reflecting geographic and ethnic diversity. As also noted for the adult population, coexisting PTC with HT in childhood is associated with favorable prognoses arguably due to the ‘protective’ immune phenomenon controlling the proliferation of malignant cells. Patient management meta-analytical studies demonstrate favorable outcomes and prognoses in patients with coexisting PTC and HT. For such patients at presentation, the typical clinical parameters include: a female gender prevalence, multifocal nodularity, no extrathyroidal extension, no lymph node metastases and longer recurrence-free survival rates. Nevertheless, the biological coexistence of HT and PTC remains controversial. Some researchers have suggested that HT induces PTC, but conversely, that lymphocytic infiltration in HT may result from an autoimmune reaction against tumor-specific antigens from pre-existing PTC. Recent work reports a higher prevalence of activating point mutations in BRAF V600E in cases of PTC with an associated poor prognosis. Relevant studies on Korean patients demonstrate the presence of BRAF V600E mutation to be linked with a higher likelihood of lymph node metastases and a lower frequency of HT. Therefore, these findings support the hypothesis that HT may pose a ‘protective’ immune response in patients with concomitant PTC.