The forgotten lobe in focus: a rare case of isolated pyramidal lobe papillary thyroid carcinoma

Abstract

Introduction and importance:

Isolated papillary thyroid carcinoma (PTC) arising from the pyramidal lobe (PL) is an uncommon entity that may clinically present as a midline neck swelling, often mimicking a thyroglossal duct cyst and thyroglossal duct cyst carcinoma.

Case presentation:

A 46-year-old woman presented to the clinic with a solitary, midline neck swelling that was firm and mobile. The patient underwent relevant investigations, and the diagnosis was confirmed to be isolated PTC of the PL. The patient underwent total thyroidectomy and had an uneventful recovery without residual or metastatic disease.

Clinical discussion:

Isolated PL PTC poses a diagnostic challenge due to its clinical and radiological resemblance to thyroglossal duct cyst carcinoma and Delphian node metastasis. Failure to recognize this entity may lead to inadequate surgical management. Given its reported association with extrathyroidal extension, multifocality, vascular invasion, and a possibly aggressive molecular profile, comprehensive surgical evaluation, including total thyroidectomy, should be considered to reduce recurrence risk and facilitate postoperative surveillance.

Conclusion:

A high index of suspicion, detailed imaging of the midline neck structures, and awareness of embryological variants are essential to avoid misdiagnosis and ensure optimal oncological treatment in cases of PTC of the PL.

Introduction

The thyroid gland is the largest endocrine gland located in the anterior aspect of the neck. It consists of two lobes, right and left, connected by a narrow isthmus. The pyramidal lobe (PL) of the thyroid gland represents the vestigial remnant of the distal part of the embryonic thyroglossal duct. It is usually connected to the isthmus; however, it displays anatomical variations^[1,2^]. The PL is believed to be present in about 15% to 75% of the population ^[3,4^]. Papillary thyroid carcinoma (PTC) is the most common histologic type of differentiated thyroid cancer with a favorable prognosis^[5^]. PTC most commonly arises from the right lobe, followed by the left lobe, and less commonly from the isthmus^[6^]. PTC arising mainly from the PL is extremely rare^[7^]. This form of malignancy is rare, with only limited case reports and small case series described in the literature^[8–10^]. This case is peculiar for two reasons: first, being a very rare entity, and second, having clinical and radiological features similar to midline neck swelling, particularly thyroglossal duct cyst carcinoma (TGDC) and Delphian node metastasis. In this case, we reflect on our experience of successful management of a papillary carcinoma thyroid arising from the PL.

HIGHLIGHTS

• Isolated papillary carcinoma of the pyramidal lobe of the thyroid is a rarity and presents as a midline neck mass.

• It needs to be distinguished from other causes of midline neck masses, such as thyroglossal duct cyst, thyroglossal duct cyst carcinoma, and Delphian node metastasis.

• Total thyroidectomy is the treatment of choice to improve the prognosis.

This case report has been reported in line with the SCARE checklist^[11^].

Case report

Case history and examination

A 46-year-old non-alcoholic, non-smoker, hypertensive, and diabetic woman without any significant family history presented to our otorhinolaryngology clinic with a complaint of a single midline swelling in the anterior aspect of the neck for a month. The swelling initially appeared small and was painless but gradually increased in size over the course of a few months. There was no difficulty in swallowing, voice changes, pressure symptoms, restricted neck movements, or fever. There were no features of hypo- or hyperthyroidism.

On examination, a 2 × 2 cm firm, non-tender, mobile swelling was noted in the submental region, which moved on swallowing. No cervical lymphadenopathy was palpated. The thyroid gland was not enlarged on palpation, and no discrete nodules were appreciated in either lobe. The swelling did not move with tongue protrusion, thereby reducing suspicion of a thyroglossal duct cyst (Fig. 1). The remainder of the head and neck, along with the general physical examination, was unremarkable.

Figure 1.

Clinical photograph showing a 2 × 2 cm firm, non-tender, mobile swelling was noted in the submental region (black arrow).

Investigations and treatment

Ultrasonography revealed a well-defined hypoechoic lesion in the submental region, with a differential diagnosis of a thyroglossal duct cyst; the thyroid gland otherwise appeared unremarkable. Fine-needle aspiration cytology (FNAC) was reported as Bethesda V, suspicious for PTC. Given the high index of suspicion, a contrast-enhanced CT (CECT) scan of the neck was performed, which demonstrated an irregular, heterogeneously enhancing soft tissue lesion measuring 2.2 × 1.3 × 1.7 cm in the anterior superficial aspect of the right lobe/PL region (Fig. 2). No radiologically suspicious central (level VI) or lateral cervical lymph nodes were identified on ultrasonography or the CECT scan. Based on these findings, a diagnosis of PL PTC was suspected, and the patient was planned for total thyroidectomy following a complete preoperative workup. Intraoperatively, a 2 × 2 cm firm-to-hard swelling was identified in the PL, confirming the preoperative suspicion (Fig. 3). The remaining thyroid lobes and isthmus appeared normal, and a total thyroidectomy was performed.

Figure 2.

A contrast-enhanced computed tomography of the neck demonstrating an irregular, heterogeneously enhancing soft tissue lesion measuring 2.2 × 1.3 × 1.7 cm in the anterior superficial aspect of the right lobe/pyramidal lobe region (black and white arrow).

Figure 3.

A clinical image showing the final operative specimen of 2 × 2 cm firm-to-hard swelling in the pyramidal lobe (black arrow) with normal bilateral thyroid lobes.

Result and conclusion

Postoperatively, the patient had an uneventful recovery and was discharged on the second postoperative day. Histopathological examination demonstrated classical papillary architecture with fibrovascular cores and characteristic nuclear features, including ground-glass nuclei, nuclear grooves, and nuclear overlapping. Focal vascular invasion was identified. The final pathological staging was pT2Nx (Fig. 4). A radioactive iodine (RAI) scan performed 4 weeks later showed no residual or metastatic disease.

Figure 4.

Histopathological image showing features suggestive of papillary thyroid carcinoma, classic subtype, of an isolated pyramidal lobe.

Discussion

PTC of the PL is extremely rare. In contrast to earlier reports suggesting an occult PTC prevalence of approximately 0.4%, Wen et al demonstrated occult PTC in 4.72% of patients undergoing thyroidectomy, indicating that subclinical disease may be underrecognized^[6,12^]. PL PTC usually manifests as a smaller nodule but has a more sinister course in the form of extrathyroidal extension, lymphatic invasion, advanced staging, and multifocal location^[8–10^]. However, in our case, the patient reported none of these features except for one, i.e., a nodule measuring 2.5 × 1.5 × 1.3 cm with vascular invasion. FNAC, high-resolution ultrasonography of the neck, and CECT of the neck are the preoperative diagnostic approaches; however, intraoperative findings and histopathological considerations are also crucial for the diagnosis. The histopathological absence of thyroglossal duct epithelial lining and ectopic thyroid follicles excluded the diagnosis of TGDC^[13,14^]. Interestingly, PL-PTC appears to exhibit a higher prevalence of the BRAF V600E mutation compared to PTC arising from other thyroid regions, potentially suggesting a distinct molecular profile^[12^]. However, due to the unavailability of mutation analysis at our center, we could not perform this test. PTC of the PL has significant clinical and radiological similarities – presenting as a cystic midline mass with high diagnostic heterogeneity – with Delphian node metastasis and thyroglossal duct cyst (TGDC) carcinoma. Hence, this highlights the need to group these conditions under one umbrella term – upper neck papillary thyroid cancer^[10^]. Orthotopic thyroid resection has a role in cases of PTC of PL and Delphian node metastasis, whereas the Sistrunk operation is usually the treatment of choice for thyroglossal duct cyst and TGDC^[10,14^]. Even though surgery remains the mainstay of treatment for papillary thyroid cancers, there is no consensus regarding the extent of surgery and the management after surgery in cases of PTC arising from the PL due to the paucity of cases^[15^]. In our case, keeping in mind the high recurrence rate and characteristic multifocality of PTC of the PL, we performed total thyroidectomy^[16^]. Approximately 50% of patients who undergo radioiodine treatment following total thyroidectomy have residual thyroid tissue, with about 4% showing occult PTCs in the same area^[4^]. However, in our case, the RAI scan after 4 weeks revealed no residual or metastatic disease, thus highlighting the oncological importance of total thyroidectomy in PTC of the PL.

Conclusion

PTC of the PL is a rare but clinically significant entity that can mimic other midline neck pathologies. Accurate preoperative identification is essential to prevent undertreatment. Given its potential for vascular invasion, multifocality, and possible distinct molecular characteristics, total thyroidectomy may provide optimal oncologic control. Larger multicenter studies are required to establish evidence-based surgical and postoperative management guidelines.

Ethical approval

The study is exempt from ethical approval at our institution.

Consent

Written informed consent was obtained from the patient to publish this report in accordance with the journal’s patient consent policy.

Sources of funding

None.

Author contributions

Conceptualization, investigation, and methodology: K.M. and R.M. Writing - original draft: A.J., A.L., and S.Y. Writing–review and editing: K.M. and A.J.

Conflicts of interest disclosure

None.

Research registration unique identifying number (UIN)

The study does not have a trial registry number.

Guarantor

Kajal Mahto.

Provenance and peer review

Not applicable.

Data availability statement

Not applicable.