(6.01) Papillary Thyroid Microcarcinoma Presenting as a Palpable Neck Mass

Papillary thyroid microcarcinoma (PTMC) is subgroup of papillary thyroid carcinoma (PTC) defined by tumors ≤ 10 mm in largest diameter.  PTMC now accounts for approximately half of all new diagnoses of PTC.  Though the majority of PTMC cases are low stage and amenable to disease-free state after thyroid surgery, PTMC may be complicated by lymph node metastases.  We present a case of PTMC diagnosed during evaluation of a visible neck mass.

Case(s) Description :

A 54-year-old male presented to his primary care provider for evaluation of a visible right anterior neck mass.  Ultrasonography revealed a 3.8 cm level IV lymph node with abnormal morphology, but no thyroid nodules were observed.  Fine-needle biopsy of the lymph node yielded cytology notable for a small number of atypical appearing thyroid follicular cells expressing thyroid transcription factor-1 (TTF-1), and thyroglobulin was easily detectable on needle washout.  The initial diagnosis of metastatic PTC was confirmed on fresh-frozen sections following lymph node resection, prompting thyroidectomy and dissection of right level III and IV lymph nodes. Postsurgical histopathology identified a 2 mm right thyroid lobe PMTC, and all other lymph nodes were free of metastatic thyroid cancer.  After recovery from surgery, the patient was treated with radioiodine (163 mCi).  In the seven years since surgery and treatment with radioiodine, there has been no radiologic, serologic, or clinical evidence of thyroid cancer persistence or recurrence.

Discussion : PMTC is a cancer considered to have an excellent prognosis, and approximately one-third of cases are diagnosed incidentally after thyroidectomy.  However, a surprising proportion of PMTC cases are complicated by lymph node metastases.  In a single institution series of 177 patients with PMTC at Wroclaw Medical University (Poland), lymph node metastases were present in 35% of cases, and the rate of lymph node metastases was 26% in a systematic review that included data from 60 articles.  Multifocal tumors, bilateral tumors, and tumor size ≥ 5 mm have been identified as independent predictors of increased risk for cervical metastases in cases of PMTC.  This case is unusual because the patient had none of these risk factors, though his tumor expressed TTF-1, a gene important in thyroid organogenesis and shown to be highly expressed in some cases of aggressive PTC.  PMTC has potential to metastasize outside the thyroid gland and is the presumptive primary tumor in patients with metastatic thyroid carcinoma but no radiographically detectable thyroid mass.