Rare location of head and neck adenoid cystic carcinoma

Adenoid Cystic Carcinoma of larynx is extremely rare location. We herein describe an unusual clinical and radiological presentation of ACCL and review recent literature. We report a case of a 38-year-old woman with history of asthma, presented to our department with acute inspiratory dyspnea that required an emergency tracheotomy. Physical examination revealed a large anterior cervical mass without any lymphadenopathy suspecting thyroid origin. Cervical Computed Scan showed a tumor process between the thyroid lobe, the left edge of the subglottic area and first tracheal rings filling all the lumen, discussing either a laryngo-tracheal or thyroid origin. The patient underwent a panendoscopy under general anesthesia that confirmed a subglottic extension of the tumor and multiples biopsies showed a malignant salivary origin of the mass. After multidisciplinary discussion, the patient underwent total laryngectomy and thyroidectomy with bilateral selective neck dissections (levels II- IV). Anatomopathological examination confirmed the laryngeal location of Adenoid Cystic Carcinoma classified pT4aN0R0. Adjuvant radiation therapy was indicated. In our knowledge, only 10 cases were reported in the literature with this unusual presentation. Moreover, the case we report is in the subglottic floor without invasion of neither vocal cords nor trachea. Total laryngectomy with neck dissection remains the recommended therapeutic procedure for locally advanced ACCL. Adverse features such as close or positive margins, T3-4, intermediate or high grade neural and perineural spread, lymphatic or vascular invasion or lymph node metastases should indicate adjuvant treatment to improve the outcome. The lack of randomized multicentric study, implies the management of ACCL by skilled multidisciplinary team, to suggest adequate personalized treatment.


Introduction
Adenoid Cystic Carcinoma is a common tumor of salivary glands. Due to the very low density of minor glands in the larynx (23 -47 glands/cm 2 ) versus oral cavity for example (600-1000 glands/cm 2 ), the incidence of adenoid cystic carcinoma of the larynx "ACCL" is extremely rare (<1% of all laryngeal cancer) [1]. Clinical symptomatology of ACCL is dominated by dyspnea and hoarseness.
Subglottic location is clearly the most common while distribution by gender remains controversial [2]. ACCL are reputed by the frequency of late distant metastasis and local recurrence, though they are slow growing malignant tumors. Adenoid cystic carcinoma is categorized in three subtypes: Cribriform witch is the most common, tubular form with good prognosis and finally Solid subtype characterized by poor outcome [2][3][4]. We report, a new case of ACCL with unusual clinical presentation as we suspect a thyroid mass despite paraclinical investigations the initial site of the tumor couldn't be specified, it's only after the pathological examination of the operative specimen that the laryngeal origin was confirmed.
The recent systematic review of Marchiano et al. reports that ACCL occurs in both sex with slightly predominance in men [5], the median and mean age reported is the fifties with clear predominance of white race [5,8]. We report a new case of Adenoid Cystic Carcinoma of Clinical and paraclinical investigation didn't identified clearly if the starting point was thyroidian or laryngotracheal. In our knowledge, only 10 cases were reported in the literature with this unusual presentation [9]. In our case, the tumor was subglottic without invasion of neither vocal cords nor trachea. These findings are rare as the majority of cases reported in the literature had trachea as primary site [10][11][12][13]. Treatment modalities of ACCL remains non-standardized due to their rarity. Surgery is the cornerstone of treatment [8]; however, the appropriate surgical resection is not standardized yet.
Indeed, some authors preferred radical surgery [1,3,14] even if wide local excision allowed to preserve laryngeal function. Their choice is argued by the relative radio resistance of this kind of tumor [15] as ACCL are radiosensitive but not radio curable [1,5]. However, British experience supports that combined treatment with preservative surgery and post-operative radiotherapy led to reduce loco-regional recurrences [16]. This objective was achieved in many studies with excellent loco-regional control thanks to addition of radiotherapy in various studies conducted in the MD Anderson Cancer Center [17,18].
In fact, some adverse features had significant influence on local Page number not for citation purposes 3 control such as margins, tumor size, perineural invasion [18,19]

Conclusion
Adenoid cystic carcinoma of the larynx is an extremely rare malignant neoplasm. Surgical resection with neck dissection is the main treatment of non-metastatic tumor, however combined modality treatments greatly improves loco-regional outcome.

Competing interests
The authors declare no competing interests.

Authors' contributions
All the authors have read and agreed to the final manuscript.