INTRODUCTION
The pyramidal lobe of the thyroid gland is present in 15-75% of the population. [1] On the other hand, papillary thyroid carcinoma (PTC) of the pyramidal lobe, defined as a single pyramidal lobe cancer or multifocal cancer in which pyramidal lobe tumor is the largest, is extremely rare. [2,3] Because of this, the clinical and pathological characteristics of these PTCs are not well understood. [3]
The authors describe a case of PTC of the pyramidal lobe and its clinical implications according to a revision of the current scientific literature.
CASE PRESENTATION
A 77-year-old female patient was referred to the Head and Neck Surgery department of the Portuguese Institute of Oncology of Lisbon, because of a midline neck mass, present at least for ten years, but with progressive growth in the previous nine months [Figure 1] . The remaining head and neck and general physical examination was unremarkable. She had a personal history of obesity (BMI 38.16 Kg/m2), asthma, obstructive sleep apnea, hypertension, dyslipidemia and depressive disorder, and a family history of unspecified breast cancer (sister). She denied smoking, high alcohol intake or other family history of cancer or endocrine disease.
The patient was accompanied with a neck CT scan and ultrasound that had identified two thyroid nodules – the largest one with 25mm located in the pyramidal lobe [Figure 2] and another with 21mm located in the right lobe [Figure 3] , both were TI-RADS 5 and suggestive of papillary thyroid cancer (PTC) after fine needle aspiration cytology (FNAC). General and endocrine blood tests, including TSH, T4 hormone and calcitonin, were within normal values range.
In our hospital, the review of the cytology samples confirmed the diagnosis and after the decision of the treatment by the multidisciplinary team (MDT), the patient underwent a total thyroidectomy en bloc with the pyramidal lobe and hyoid bone.[Figure 4,5,6] In addition, intraoperatively, the presence of suspicious lymph nodes in the central compartment of the neck led to a lymph node dissection at this level. It was not possible to preserve the right recurrent laryngeal nerve because of direct invasion of the cancer. Finally, due to the close proximity of the main malignant nodule to the trachea, tracheal shaving was also performed.
The immediate postoperative period was complicated by dyspnea and the need for tracheostomy, which the patient maintained at the time of hospital discharge. The laryngoscopy, performed during hospitalization, identified bilateral paralysis of the vocal cords. There were no other inward complications, including hypocalcemia.
The histologic result reported a multifocal papillary thyroid cancer, with the largest node at the pyramidal lobe (maximal dimension of 25mm), with extrathyroidal extension and lymphovascular invasion, as well as metastasis in two central compartment lymph nodes. [Figure 7,8] The TNM staging was pT3bpN1a. This time, the MDT decided for adjunctive treatment with radioiodine therapy.
Currently, at six months of follow-up, the patient was finally able to remove the tracheostomy after verified mobility of the left vocal cord and permeable glottis on laryngoscopy. No other incidents were reported during follow-up. Also, body scintigraphy and neck CT scan confirmed absence of local or regional disease.
DISCUSSION
The widespread availability of imaging modalities, such as high resolution ultrasound and ultrasound guided FNAC have contributed to the higher detection of thyroid carcinoma. [4] The most frequent histologic type of thyroid carcinoma is papillary carcinoma, accounting for approx. 80% of differentiated thyroid carcinomas. [5] Although PTCs are generally associated with an indolent clinical course and favorable prognosis – 10 year relative survival rate of 93% – recurrence is significant at 5-20%. [6] This is specially associated with advanced age, male gender, tumour size, multifocality, extrathyroidal extension, extranodal spread and lymph node ratio. [7] The pyramidal lobe of the thyroid gland, usually connected to its isthmus, is located in the inferior portion of the thyroglossal duct, a remnant of the embryological development of the thyroid. [1] It is reported to be present in 15-75% of the population. [1] On the other hand, papillary thyroid carcinoma (PTC) of the pyramidal lobe is extremely rare, thus, the clinical and pathological characteristics of these PTCs are not well understood. [1,2] In comparison with papillary thyroid carcinoma of other locations, pyramidal lobe PTC was found to have a more advanced patient age at diagnosis (mean of 58 vs 43 years old), smaller nodule dimension, but more frequent extrathyroidal extension, lymphatic invasion, advanced AJCC staging and multifocal location. [3] These associations are supported in the present case: our patient exhibited all but one (smaller nodule dimension) of the previous reported adverse features, which correlated with a more aggressive disease, specifically the close relation of the cancer lesion with the trachea and direct invasion of right recurrent laryngeal nerve during thyroidectomy and long period of tracheostomy dependency. Even though, these features also put the patient at increased risk of recurrence [7], there were no signs or symptoms of recurrence at the latest follow-up of 6 months after surgery. Zizic M et al. identified a high diagnostic heterogenity in the scientific literature concerning not only pyramidal lobe papillary carcinoma, but also Delphian node metastasis and thyroglossal duct cysts (TGDC) carcinoma, that may explain the controversy in managing these patients. In order to address the issue, a new terminology to group these entities was created – Upper neck papillary thyroid cancer (UPTC). [Table 1] [8] The clinical distinction between these entities has important implications for the patient’s treatment, namely decision for orthotopic thyroid resection, which is generally recommended in the presence of PTC in the pyramidal lobe, metastasis to the Delphian node and indetermined origin, but not in TGDC papillary carcinoma. [8] The reported presence of residual thyroid tissue in patients submitted to radioiodine treatment after total thyroidectomy is approx. 50%, and the rate of occult PTCs in the same location is around 4%. [3,9] These reports highlight the oncological importance of the complete resection of the pyramidal lobe during thyroidectomy in papillary thyroid carcinoma, namely the possibility to improve radioiodine treatment efficacy or facilitating postoperative follow-up surveillance with scintigraphy or blood thyroxine values. [9,10] The characteristic multifocality of PTC and the activation of the residual pyramidal lobe when it is not removed during thyroidectomy, also make the pyramidal lobe a potential place for recurrent PTC. [7] In conclusion, papillary carcinoma of the pyramidal lobe is a rare diagnosis, but associated with adverse prognostic features. A new classification of Upper Neck Papillary Carcinoma (UPTC) further distinguishes papillary pyramidal lobe carcinomas from PTCs of other thyroid locations. This pathological entity was proposed to facilitate the analysis of the literature, the diagnostic investigation and the decision for the treatment. Complete excision of the pyramidal lobe during total thyroidectomy for papillary carcinoma may have important implications for the effectiveness of adjuvant radioiodine therapy as well as for patient’s follow-up surveillance and risk of recurrence. Future studies are needed to better understand the usefulness of the reported new terminology, as well as the clinical behavior and implications of the pyramidal lobe in the surgical and adjuvant treatment of these rare thyroid carcinomas.
REFERENCES
  1. Braun EM, Windisch G, Wolf G, Hausleitner L, Anderhuber F. The pyramidal lobe: clinical anatomy and its importance in thyroid surgery. Surg Radiol Anat 2007;29:21-7.
  2. Santrac N, Besic N, Buta M, Oruci M, Djurisic I, Pupic G, et al. Lymphatic drainage, regional metastases and surgical management of papillary thyroid carcinoma arising in pyramidal lobe – a single institution experience. Endocr J 2014;61: 55-9.
  3. Yoon SG, Yi JW, Seong CY, Kim JK, Kim SJ, Chai YJ, Choi JY, Lee KE. Clinical characteristics of papillary thyroid carcinoma arising from the pyramidal lobe. Ann Surg Treat Res. 2017 Mar;92(3):123-128.
  4. Van Den Heede K, Tolley NS, Di Marco AN, Palazzo FF. Differentiated Thyroid Cancer: A Health Economic Review. Cancers (Basel). 2021 May 7;13(9):2253.
  5. Grant CS. Recurrence of papillary thyroid cancer after optimized surgery. Gland Surg 2015;4:52–62.
  6. Liu FH, Kuo SF, Hsueh C, et al. Postoperative recurrence of papillary thyroid carcinoma with lymph node metastasis. J Surg Oncol 2015;112:149–54.
  7. Wang M, Zou X, Li Z, Zhu J. Recurrence of papillary thyroid carcinoma from the residual pyramidal lobe: a case report and literature review. Medicine (Baltimore). 2019 Apr;98(15):e15210.
  8. Zizic M, Faquin W, Stephen AE, Kamani D, Nehme R, Slough CM, Randolph GW. Upper neck papillary thyroid cancer (UPTC): A new proposed term for the composite of thyroglossal duct cyst-associated papillary thyroid cancer, pyramidal lobe papillary thyroid cancer, and Delphian node papillary thyroid cancer metastasis. Laryngoscope. 2016 Jul;126(7):1709-14.
  9. Zeuren R, Biagini A, Grewal RK, Ran- dolph GW, Kamani D, Sabra MM, et al. RAI thyroid bed uptake after total thy- roidectomy: A novel SPECT-CT anatomic classification system. Laryngoscope 2015; 125:2417-24.
  10. Sinos G, Sakorafas GH. Pyramidal lobe of the thyroid: anatomical considerations of importance in thyroid cancer surgery. Oncol Res Treat. 2015;38(6):309-10.