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－ Case Reports － Clinical Utility of Fine Needle Aspiration Cytology for Adenoid Cystic Carcinoma of the Trachea with Thyroid Invasion: A Case Report

after the surgery. Conclusions: ACCT with thyroid invasion is an extremely rare malignant neoplasm. FNAC was useful for differentiating ACCT from other diagnoses and enabled appropriate surgical treatment.


Introduction
Adenoid cystic carcinoma (ACC) is a rare cancer with an annual incidence of less than 6 per 100,000 population 1 . ACC was first described as cylindroma by Billroth in 1853, with its current name proposed by Spies in 1930 2 . ACC is categorized into three subtypes. It typically presents with a cribriform pattern. A tubular form shows good prognosis, whereas the third subtype is solid and is characterized by poor outcomes. ACC of the trachea (ACCT) is rare, with an overall annual incidence of less than 0.2 per million 3 .
ACCT with thyroid invasion is extremely rare. The predominant clinical symptoms of ACCT are dyspnea and hoarseness, and the tumor is slow-growing malignancy.
Anaplastic thyroid carcinoma (ATC) is the most aggressive type of thyroid cancer, and indeed one of the fastest-growing and most aggressive of all cancers. ATC is rare, being found in less than 2% of patients with thyroid carcinomas. Some patients with ATC present with acute respiratory symptoms because of the tracheal invasion.
Fine needle aspiration cytology (FNAC) is an important diagnostic tool because of its simplicity, safety, and cost-effectiveness. It is becoming a popular procedure for diagnosing thyroid diseases.
In this case, we initially suspected ATC. The original site of the tumor could not be identified through paraclinical investigation. Emergency tracheotomy was required 6 because of acute inspiratory dyspnea. After this procedure, we conducted FNAC and diagnosed ACC. The tracheal origin of the tumor was confirmed only after pathological examination and diagnosis of the operative specimen. In the present paper, we described the case of tracheal adenoid cystic carcinoma extending into the thyroid gland, which apparently looked like thyroid carcinoma in the radiological examination but was successfully diagnosed by FNAC.

Case report
A 77-year-old Japanese woman with a history of duodenal ulcer, ganglion cyst of the knee, and iodinated contrast dye allergy presented to the thyroid hospital with acute inspiratory dyspnea that required emergency tracheotomy. She had suffered from hoarseness for 4 months.
Physical examination revealed right anterior neck swelling with a hard and unmovable mass. Laboratory tests showed that blood levels of thyroid function tumor extending to the right thyroid lobe and peritracheal tissue, as well as severe stenosis of the lumen between the first and third tracheal rings (Fig. 1). Imaging showed extension of the tumor obstructing the trachea, but we could not determine the original tumor site and it was difficult to distinguish the cervical esophagus from the mass.
We then performed FNAC of the upper right lobe of the thyroid with a 22-gauge needle under US guidance. The specimens were stained using the Papanicolaou method.
At medium power, aspiration cytology revealed loosely cohesive sheets and threedimensional clusters of tumor cells against a clear background ( Fig. 2A). Under high power, aggregates of small round cells surrounding light green homogeneous material 8 were observed (Fig. 2B). These cells had limited cytoplasm, indistinct cytoplasmic borders, and evenly distributed chromatin. Pale green globules near the tumor cells were noted (Fig. 2C). These cytological features are suggestive of ACC. No other characteristics indicative of ATC or other thyroid carcinomas were observed. The medullary carcinoma was also ruled out by the blood data. On the basis of the clinical data, invasion of tracheal ACC into the thyroid gland was strongly suspected rather than tracheal invasion by thyroid carcinoma.
Since the lesion had spread to the trachea, thyroid gland, and cervical esophagus, it was thought to require pharyngo-laryngo-esophagectomy, and the patient was referred to a hospital specializing in head and neck cancer. The patient was transferred and underwent total pharyngo-laryngo-esophagectomy, and thyroidectomy with bilateral selective neck dissection (level II-IV). Macroscopic observations confirmed the tracheal location of the tumor (Fig. 3). The tumor was located in the right posterior wall of the trachea, between the cricoid cartilage and the third tracheal ring with extension to the right thyroid gland. The tumor was 5.3 × 3.2 × 2.8 cm in size. Pathological examination showed that the tumor originating from the trachea had directly infiltrated the adjacent thyroid gland (Fig. 4A), and that the surrounding soft tissue in contact with the wall of the esophagus was involved (Fig. 4B). The tumor cells were arranged in tubular and 9 cribriform patterns that suggested ACC. Immunohistochemical expression of fatty acid binding protein 7 (FABP7) was apparent (Fig. 4C). Overall, the tumor exhibited morphological features consistent with ACCT. It has been suggested that FABP7, a Notch signaling-related protein, could be a prognostic marker for ACCT. TNM staging was performed using the system proposed by Bhattacharyya 4 for staging primary ACCs of the trachea. The tumor was classified as pT4N1 (T4: spread to adjacent organs or structures, N1: clinical or histological evidence of regional nodal disease) because it had infiltrated the thyroid gland and adjacent soft tissue, and invaded the perineural and muscle tissues.
There were metastases to bilateral regional neck lymph nodes. Histopathology provided a definitive diagnosis of ACCT. Three years after surgery, lung metastases were observed. the thyroid. Am J Clin Pathol. 2004;121(4):551-556.