Isolated Papillary Thyroid Carcinoma of the Pyramidal Lobe: A Case Report and Review of Literature

Abstract

The pyramidal lobe (PL) represents an embryological remnant of the thyroglossal duct. A solitary focus of papillary thyroid carcinoma (PTC) of the PL of thyroid gland is a rare entity. We present a case of a 33-year-old woman with PTC of the PL with lymph nodal involvement and further discuss the lines of surgical management for primary PTC arising from the PL of thyroid gland.

Introduction

The pyramidal lobe (PL) represents an embryological remnant of the thyroglossal duct. It is considered a normal component of the thyroid gland with an incidence of 15–75% in the general population, as per various studies [1]. Lately, PL is receiving more surgical attention, especially in thyroid malignancies. Preservation of PL in thyroid malignancy surgeries may result in recurrences, render postoperative radioactive iodine ablation ineffective, and decrease the sensitivity of serum thyroglobulin in postoperative surveillance [2].

Papillary thyroid carcinoma (PTC) is the most common histological variant, accounting for 80% of all differentiated thyroid malignancies [3]. Up to half of the PTCs exhibit multifocality, which may also involve a PL if present. Isolated PTC in the PL with otherwise normal thyroid glands is extremely rare, with one large study reporting its incidence to be as low as 0.4% of all PTCs [2]. Surgical management of isolated PTC of PL remains debatable. Few authors advocate total thyroidectomy with neck dissection as the primary management [2, 4], while others recommended a more conservative approach with isthmusectomy and close surveillance [5]. Here, we report a case of an isolated PTC of the PL and discuss the management strategies for this rare entity.

Case Report

A 33-year-old female presented to us with a history of midline neck swelling for 20 years. She noticed that this swelling had been gradually increasing in size in the last 10 years but had not sought medical attention as she was devoid of any symptoms. She had no other associated symptoms and her family and medical history were unremarkable.

On examination of the neck, there was a firm, non-tender swelling of approximately 3 × 2 cm, slightly left of the midline in the anterior portion of the neck, extending from the level of the thyroid notch to the cricoid ring. The patient had a normal thyroid profile with a TSH of 2.30 µIU/mL. The neck ultrasonography described a large mixed solid-cystic nodule of size 3.3 cm (T) x 2.1 cm (AP) x 2.7 cm (CC) at the junction of the left lobe and isthmus, with multiple micro and macro calcifications and was classified as TIRADS- 3 lesion (according to the American College of Radiology scoring system). Another small nodule of size 1.3 cm x 0.8 cm was observed adjacent to the aforementioned nodule, with peripheral hypoechoic halo, and was classified as TIRADS-4 lesion.

Fine needle aspiration of the nodule revealed clusters and monolayer sheets of follicular cells, which had regular round to oval nuclei and evenly distributed chromatin. Many pigment-laden cyst macrophages were seen in a background of abundant colloid. The lesion was reported as Atypia of Undetermined Significance (AUS), or Bethesda III, according to the Bethesda system of reporting thyroid cytopathology.

A left hemithyroidectomy was performed wherein, intraoperatively, there was a spherical swelling of approximately 3 × 3 cm surface that surrounded the thyroid cartilage with nodularity to its right. The swelling appeared to arise from the isthmus, but had fibrous attachments to the left thyroid lobe, which appeared normal (Fig. 1). The histopathology of the specimen revealed papillary carcinoma of the thyroid (classical type) of the PL. Two peri-thyroid lymph nodes were also identified, the largest demonstrating tumor deposits, conferring the lesion the pathological stage - pT2N1. (Fig. 2)

Fig. 1.

(a) Intraoperative photo depicting a normal left lobe thyroid (blue arrowhead) and a large globular swelling (black arrow) superior to it; (b) Excised specimen

Fig. 2.

(a) Left hemithyroidectomy with a cut surface of the pyramidal lobe showing solid gray-white growth (red asterisk) and enlarged perithyroid lymph node (green asterisk); (b) tumor comprising arborising papillae with thin fibrovascular core along with colloid-filled areas (H&E stain, 40×) ; (c) higher magnification showing tumor cells with PTC-like nuclear features consisting of nuclear clearing, grooving, and occasional pseudo-inclusions (H&E stain, 400×); (d) Perithyroid lymph node displaying complete involvement by metastatic deposits of PTC (H&E stain, 40×)

Subsequently, completion thyroidectomy was performed considering the histopathological picture. During the second look surgery, the right lobe of thyroid appeared normal, and the level-VI lymph nodes were removed for further examination. The histopathology of the specimen showed no residual tumour and level- VI lymph nodes were also found to be free of tumour.

The postoperative period was uneventful and further radioactive iodine scans have been planned for the patient in due time.

Discussion

The PL is an anatomical variant of the thyroid gland believed to arise from the inferior portion of the thyroglossal duct, an embryological remnant that normally involutes by adulthood. Given the high incidence of the PL in the general population (up to 75%), accurate knowledge about the anatomy and its clinical implications is warranted. The PL predominantly arises from the left side of the isthmus with an average length of around 2 cm [6]. Failure to identify and remove PL can lead to recurrences in the future, as the remnant PL may potentially harbor tumour foci [7, 8]. Additionally, if the PL is preserved, it can absorb radioactive material during adjuvant radioiodine therapy, affecting its efficacy [2].

The importance of PL in malignant thyroid gland disease has recently been highlighted by few studies. Zizic et al. have proposed a new term Upper Neck PTC (UPTC) comprising thyroglossal duct cyst (TGDC)-associated PTC, PL PTC, and Delphian node PTC metastases. They observed that there can be substantial variability in pathological findings in such entities, which may create a diagnostic challenge. Many cases in their cohort were initially labeled as cancer associated with TGDC, but upon further detailed examination by the same authors, they were reclassified as PL PTC and Delphian node PTC [9].

The National Comprehensive Cancer Network (NCCN) guidelines have broadly defined the surgical management of PTC, but little is conveyed about the extent of surgery for rarer presentations such as PL PTC. Yoon et al. [10] has the largest study yet, of 49 cases of PTC arising from PL out of which 10 were assigned ‘Pyramidal lobe dominant PTC’. Of these 10 cases, 5 had a primary focus on PTC of PL. Their study highlighted that pyramidal lobe dominant PTC in general had poorer prognostic characteristics, including a higher stage of AJCC at presentation, cervical lymph nodal metastasis (50%) and BRAF mutations (70%). The authors advocated orthotopic thyroid surgery in all cases of PL-associated PTC due to the high rates of concurrent thyroid gland cancer. In our case, a complete thyroidectomy was performed and the residual right lobe of thyroid, and the level six lymph nodal sample was reported to be free of tumour.

Isolated primary PL PTC have been described in the past by Santrac et al. (3 cases) and Kim et al. (1 case). The former performed total thyroidectomy with adjunctive central neck dissection (CND) and the latter, bilateral modified radical neck dissection (MRND). Tumour foci in Delphian nodes positively predict the presence of metastases in the central group of lymph nodes (LN), and positive central LNs, in turn, predict the likelihood of metastases in lateral cervical LNs. US helps to detect lateral LN metastases preoperatively. The sentinel LN biopsy proved fruitful in the decision-making process for lateral neck dissection for Santrac et al. [2, 4].

Skillbeck et al. proposed a more conservative approach of ‘thyroid isthmusectomy’ for solitary lesions of the thyroid isthmus or PL less than 3 cm with cytological reports of nondiagnostic appearance, follicular cells, or suspicion of malignancy. According to the authors, leaving a cuff of normal thyroid tissue on both sides along the tracheo-esophageal grooves prevents complications such as recurrent laryngeal nerve injury or parathyroid glands in the event of secondary thyroid surgery in malignant pathology [5].

Existing knowledge cites that PTC of PL presents with poor prognostic characteristics and surgical management should include a total thyroidectomy with no less than a CND. Long-term follow-up is mandatory due to uncertainty in the course of the disease due to the paucity of literature.

Key Points

1. PTC may involve the PL as a part of multifocal disease or more rarely may arise from a single focus in the PL.

2. PTC of PL presents with poor prognostic features and warrants orthotopic thyroid surgery in all cases.

3. Prophylactic CND must be offered in all cases of PL PTC. Lateral nodal dissection (levels II to V) may be offered in nodal involvement detected on preoperative imaging and cytology or intraoperative sentinel LN biopsy.

4. Postoperative radioactive iodine scan must be performed in all cases and patients must maintain long-term follow-up.

Funding

No funding to declare.

Declarations

Informed Consent Obtained for Publication of a Case Report

Written informed consent was obtained from the patient for the publication of this case report.

Ethical Approval

Our institution does not require ethical approval for reporting individual cases or case series.