Sternal metastatectomy in a case of papillary thyroid carcinoma

Abstract

Thyroid cancer is the most common among endocrine cancers. Over 90% of all thyroid malignancies are differentiated thyroid carcinomas (DTC). However, only 2%–13% of DTC present with bone metastasis. Radioactive iodine ablation (RAI) is the treatment of choice for metastatic DTC. However, RAI therapy is not as effective in bone metastasis as it is in lung and visceral metastases. Only few cases of surgical management of bone metastasis in DTC have been reported in the literature. Here, we report a case of follicular variant of papillary thyroid carcinoma with sternal and lung metastases, for which sternal metastatectomy was performed.

BACKGROUND

Thyroid cancer is the most common among endocrine cancers.¹ The incidence of thyroid cancer is showing an increasing trend with worldwide age-standardised incidence of 4 per 100 000.² These cancers are common in people aged less than 45 years.^{1 3} This increase in incidence may be attributed to better detection rate owing to improvement in diagnostic techniques.⁴ Only 2%–13% of differentiated thyroid carcinomas (DTC) present with bone metastasis.⁵ Radioactive iodine ablation (RAI) is the treatment of choice for metastatic DTC. However, RAI therapy is not as effective in bone metastasis as it is in lung and visceral metastases.⁶ Only few cases of surgical management of bone metastasis in DTC have been reported in the literature. Here we report a case of follicular variant of papillary thyroid carcinoma with sternal and lung metastases, for which sternal metastatectomy was performed.

Case presentation

An elderly woman presented with a progressive swelling in the neck since 5 years. She also presented with another swelling in the chest wall and occasional dyspnoea since 4 months. The patient was a known diabetic and hypertensive. On clinical examination, there was a swelling in the region of the thyroid gland bilaterally, approximately 5×4 cm in size, which moved on deglutition. There was no evidence of retrosternal extension. There was another swelling in the upper middle part of the chest, approximately 6×6 cm in size. On palpation, the swelling was hard in consistency. The skin over the swelling was normal and there were no palpable nodes in the neck.

Investigations

The patient initially underwent ultrasonography (USG) of the neck which showed a 2.5×2.1 cm heterogeneous nodule in the left lobe of the thyroid with microcalcifications, and multiple nodules in the right lobe, with the largest measuring 1.9×1.5 cm. CT of chest revealed metastatic nodules in both the lungs and a destructive lesion in the sternum. The patient had previously undergone fluorodeoxyglucose (FDG)-positron emission tomography which showed a large multinodular goitre with low-grade non-uniformly hypermetabolic heterogeneously attenuating nodular lesions with calcifications and areas of necrosis in both lobes of the thyroid. The most FDG-avid nodular lesion measuring 3.95×4.25×5.09 cm was seen in the right thyroid lobe. A few prominent lymph nodes in the right cervical level II and III demonstrated increased metabolic activity, suggestive of nodal metastasis. Both lungs showed multiple low-grade FDG-avid scattered nodules. A large destructive lytic lesion measuring 4.4×5.3×5.3 cm was noted in the manubrium sterni (figure 1). USG-guided fine needle aspiration cytology (FNAC) from the right lobe of the thyroid was reported as papillary thyroid carcinoma of follicular variant. USG-guided FNAC from sternal mass was reported as metastatic papillary thyroid carcinoma of the follicular type.

Figure 1.

Sagittal section of CT scan showing thyroid and sternal mass.

Treatment

The case was discussed in multidisciplinary tumour board and taken up for total thyroidectomy, right selective neck dissection (II–IV), resection of sternal metastasis and reconstruction. The surgery was performed by head and neck surgeons in association with a thoracic surgeon. Total thyroidectomy was performed with intraoperative nerve monitoring. Metastatectomy was then performed involving the upper part of the sternum (figure 2). The defect was reconstructed with a Dacron mesh, bone cement and pectoralis major muscle flap (figure 3). Postoperatively, the patient did not show any signs of hypocalcaemia. Histopathology was reported as follicular variant of papillary thyroid carcinoma. The maximum tumour dimension was 5 cm. Lymphovascular emboli was present. All 28 nodes that were removed did not show evidence of metastasis. The sternal lesion was reported as metastatic papillary carcinoma of follicular variant with focal micropapillary features. The patient was referred to the Department of Nuclear Medicine for RAI scan and RAI ablation. She received two doses of RAI therapy.

Figure 2.

Exposed sternal mass lesion before excision.

Figure 3.

Introperative image depicting post-excision status of sternal mass lesion and reconstruction with Dacron mesh.

Outcome and follow-up

At the 6-month follow-up, the patient was asymptomatic. Post-RAI therapy scan showed no uptake in the thyroid bed and few uptakes in both lung fields. The patient is now due for her next dose of RAI.

Discussion

Over 90% of all thyroid carcinomas are differentiated carcinomas. The 10-year survival rate of DTC range from 97% to 98%. Only 2%–13% of DTC present with bone metastasis.⁷ Presence of bone metastasis drastically reduces the 10-year survival rate to 14%–21%. Follicular carcinoma has higher incidence of bone metastasis compared with papillary carcinoma.⁵ Matta-Coelho et al have shown that, among all variants of papillary carcinoma, the follicular variant has a higher incidence of bone metastasis.⁷ Thorax (18%) is the third most common site of bone metastasis from DTC after spine (35%) and pelvis (25%).⁵ Presence of both lung and bone metastases together have poor prognosis compared with metastasis only to lung or bone.⁸ RAI is the treatment of choice for metastatic DTC. Bone metastasis from DTC is treated with either RAI therapy, surgery or external beam radiotherapy.

In cases of DTC presenting with multiple metastases with a single bone metastasis, surgical resection of the bone lesion prior to RAI has been shown to improve efficacy of RAI therapy. For multiple iodine-avid bone metastases, RAI is the preferred therapeutic option.⁹ Pak et al have reported a 5-year survival rate of 78.5% and a 10-year survival rate of 50.2% after distant metastatectomy in DTC.¹⁰ Also, Zettinig et al have shown that surgical removal of isolated bone metastasis in the absence of extraskeletal metastasis improves survival.¹¹ In order to improve the treatment efficacy of RAI, we opted for surgical resection of the sternal metastasis prior to RAI ablation.

Currently, there are no standard guidelines for reconstruction following sternal resection. Acrylic resin, stainless steel mesh, titanium mesh, polypropylene mesh and polytetrafluoroethylene are some of the materials reported in the literature for sternal reconstruction.¹² We used a Dacron mesh overlaid with bone cement to cover the sternal defect and the soft tissue cover was provided with pectoralis major muscle flap.

Learning points.

• Radioactive iodine ablation (RAI) is the treatment of choice for metastatic differentiated thyroid cancers (DTC).

• Bone metastasis from DTC can be treated with RAI therapy, surgery or external beam radiotherapy.

• In cases of DTC showing multiple metastases with a single bone metastasis, surgical resection of the bone lesion can improve the efficacy of RAI therapy.

• Resection of sternal metastasis can be safely performed in cases with poor prognosis for good palliation and to increase the efficacy of RAI ablation.