Primary Synovial Sarcoma of the Thyroid Gland: A Case Report and Review of Literature

Abstract

Synovial cell sarcoma (SS) is a rare soft tissue sarcoma which can occur at any site in the body. SS arise from pluripotent mesenchymal cells and can occur in the head and neck region. We present a case of primary SS of the thyroid gland in a 47- year- old male and discuss the diagnostic and management challenge. A literature review of this rare entity was done.

Introduction

Synovial cell sarcoma (SS) is a rare soft tissue sarcoma which can occur at any site in the body. Most SS arise in the extremities, near the large joints, with a predilection to the lower extremities. SS arise from pluripotent mesenchymal cells, not from synovial tissues, [1] however the name given for their appearance and not their origin [2]. Therefore, they can also occur in any other anatomical location, including the head and neck [3]. Sarcomas of the head and neck account for approximately 1% of all head and neck malignancies. SS represents less than 10% of all primary sarcomas of the head and neck [4].

SS is classified into 2 main subtypes: biphasic and monophasic. Monophasic SS is the more common subtype and is formed of only spindle cells. Biphasic SS consist of both spindle and epithelial components. SS is characterized by a specific t(X; 18) (p11.2; q11.2) translocation leading to generation of SYT-SSX fusion gene transcripts [4]. The median age of diagnosis of SS is in the late thirties. The thyroid is an exceptionally rare site, and to our knowledge there have only been 12 reported cases of SS of the thyroid gland in the literature [[5]]. We present a case of SS of the thyroid gland in a 47 year-old male. This study was approved by The Hospital ethics' committee.

Case report

A 47-year-old male presented with progressively enlarging lower neck mass. Clinical manifestations included mild dyspnea, progressive dysphagia but without weight loss. Neck Ultrasound showed a diffuse heterogeneous echo pattern with micro-calcific foci and areas of vascularity. Fine needle aspiration Cytology (FNCA) revealed oncocytic neoplasm with atypical cells (Bethesda IV). Indirect laryngoscopy demonstrated bilateral freely mobile vocal cords and no palpable lymph node. CT with contrast (Fig. 1) showed lower neck and superior mediastinal mass encroaching upon the trachea. After discussion by tumour board, decision was done to do total thyroidectomy. Informed consent was obtained from the patient. Histopathological examination revealed a 5.5 cm lobulated mass with nodular surface. Microscopic examination revealed an invasive tumorous growth with biphasic epithelial and mesenchymal elements. Immunohistochemical testing (IHC) was negative for CD117, TTF-1, and SMA and positive for Bcl2, CD99 and TLE-1 antibody. (Figs. 2, 3) Fluorescence in situ hybridization (FISH)) technique demonstrated the characteristic t(X; 18) (p11; q11) translocation. Thus, the definitive diagnosis as primary SS of the thyroid gland was made. The patient received postoperative CRT and he is currently disease free for 12 months.

Fig. 1.

C.T neck with contrast in the coronal plane demonstrating the extent of the mass

Fig. 2.

Positive immunostaining for Bcl2. (× 200, Anti Bcl2)

Fig. 3.

Positive immunostaining for CD99. (× 200, Anti CD99)

Discussion

SS of the thyroid gland is an extremely rare, with only few published studies (Table 1). SS of the thyroid gland typically presents with a rapidly enlarging neck mass, which may be associated with compression symptoms. Unfortunately, these clinical features are not pathognomonic and present in other types of thyroid cancer. Histologically, SS can be monophasic or biphasic type [5] and in our case, the tumour was biphasic in nature.

Table 1.

Review of literature

Study	Number of cases	Age/sex	Clinical presentation	Management
Roth [6]	1	15/M	Excessive salivation/otalgia	Total thyroidectomy and cobalt therapy
Kikuchi [7]	1	60/M	Hoarseness/palpable mass	Total thyroidectomy + neck dissection + partial resection of thyroid and cricoid cartilages
Jang [8]	1	15/M	Palpable mass	Total thyroidectomy + left Neck dissection
Ryu [9]	1	72/F	Dysphagia/hoarseness/palpable mass	Total thyroidectomy + tracheal fenestration
Ghafouri [10]	1	44/F	Rapidly growing mass	Incomplete excision
Boudin [11]	1	55/M	Rapidly growing mass	Thyroidectomy with Incomplete excision, CRT + complete excision
Bansal [12]	1	28/F	Rapidly growing mass/ dysphagia/weight loss	Total thyroidectomy + resection of retrosternal tumour + RT
Murro [13]	1	41/M	Dysphonia/ left neck mass	Total thyroidectomy + subsequent total laryngopharyngoesophagectomy
Shi [14]	1	31/M	Asymptomatic mass	Total Thyroidectomy with Incomplete excision/ Chemotherapy and neck dissection at relapse
Owen [[5]]	5	37/M	Not recorded	Total Thyroidectomy with RT
		47/M	Left thyroid nodule	Total thyroidectomy + bilateral lymph node dissection
		42/M	Recurrent neck mass	Local excision
		36/M	Neck mass	Irresectable/ chemotherapy then RT and ATR inhibitor
		30/F	Right thyroid mass	Local excision

The initial work up for any patient presenting with thyroid mass is ultrasound-guided FNAC [3]. Primary SS of thyroid gland should be differentiated from other spindle cell neoplasms as well as from other common thyroid neoplasms. Thyroid carcinomas are more common and have their characteristic immunoprofile (such as thyroglobulin or calcitonin) that is not present in SS. Other spindle cell neoplasms such as Ewing sarcoma rarely occur in the thyroid gland [13,5].

SS can be easily differentiated from the other more common thyroid neoplasms. Papillary carcinomas are characterized by their oval nuclei, with nuclear grooves, intranuclear cytoplasmic inclusions and fine chromatin. Papillary carcinomas often demonstrate true papillary formations. Medullary carcinoma consists of spindle cells with neuroendocrine chromatin and variable cytoplasm; lympho/plasmacytoid cells and atypical cells. Anaplastic carcinoma demonstrate necrotic and hemorrhagic background, giant or fusiform cells, pleomorphic nuclei, prominent nucleoli, frequent and atypical mitotic figures [13].

The main differential diagnosis of Thyroid SS is Spindle epithelioid tumor with thymus like differentiation (SETTLE). SETTLE constitutes the greatest challenge for both the head and neck surgeon and the pathologist. Both entities share similar cytomorphologic features. The aspirates are usually highly cellular and show spindle cells with scanty cytoplasm, uniform oval nuclei and indistinct nucleoli. Moreover, both SETTLE and SS share similar immunohistochemical (IHC) profile. Both conditions revealed immunoreactivity to pan-CK, CD99, Bcl-2, and EMA. Positive staining for TLE-1 antibody favors SS, since SETTLE is rarely reactive for this marker [13,5].

In our case, IHC testing was negative for CD117, TTF-1, and SMA and positive for Bcl2, CD99 and TLE-1 antibody. SS was differentiated from SETTLE based on the negative staining for SMA and positive staining for TLE-1 antibody. In addition, Fluorescence in situ hybridization (FISH)) technique demonstrated the characteristic t(X; 18) (p11; q11) translocation. Thus, the definitive diagnosis as primary SS of the thyroid gland was made.

No management consensus exists for primary thyroid SS. Generally, the treatment entails wide local excision with safety margins. The role of postoperative adjuvant chemotherapy and radiotherapy (CRT) is controversial. The patients received postoperative CRT in some studies but data related to recurrence or survival advantage was not reported. Other studies reported no survival or control benefit [11,12]. In our case, total thyroidectomy was sufficient to completely excise the tumour and postoperative CRT was given. Radical surgery in the form of total thyroidectomy with partial resection of thyroid and cricoid cartilages was necessary in some reports [7].

Overall, the prognosis of thyroid SS is very unfavorable possibly due to the rare location, rapid growth, and difficult complete excision. As the published studies are limited, data related to prognosis cannot be made. Studies reported loco regional recurrence and metastatic relapse after surgery and survival was limited 3 or 36 months. Our patient did not suffer any local or distant recurrence for 12 months after surgery [7,9]. The need for follow-up surveillance for any local or distant recurrence is important [5].

Conclusion

SS is a rare clinical entity that should be always considered when dealing with thyroid mass. Identification of the t(X; 18) (p11; q11) translocation by fluorescence in situ hybridization and/or RT-PCR is essential to establish the definitive diagnosis. Generally, the treatment entails wide local excision with safety margins. The role of postoperative adjuvant chemotherapy and radiotherapy (CRT) is controversial.

Author contributions

MZ: Corresponding author; design of the study, data collection and interpretation, final approval of the manuscript; AH: data interpretation, manuscript revision and approval; SA: drafting the manuscript and data collection; AY: data collection and interpretation, final approval of the manuscript.