Introduction:

Adenoid cystic carcinoma (ACC)is a rare malignancy of salivary gland which accounts for 1-2% of all head and neck malignancies. ACC of head and neck is characterised by slow growth rate, multiple recurrences and late distant metastasis. Neck metastasis is rare and the lung is the most common site of distant me( back of the oral tongue). ACC usually arises from subepithelial layers of minor salivary glands and presentsas submucosal mass that explains why the tumours are diagnosed late, when they become large and advanced. These cancer is NOT associated to with tobacco and alcohol usage.

In ACC of base of tongue (BOT), where surgery is the primary modality of treatment with adequate margins. Conventional surgery entails cutting the lower jaw bone to access the lesion which produces moderate to severe swallowing and speech impairment. Trans oral robotic surgery (TORS) has been used for the removal of early cancers(squamous cell carcinoma) of tonsil and base of tongue which happens due to consumption of  tobacco and alcohol. As  TORS have several benefits like limited surgical morbidity, good functional outcome, shorter hospital stay and improved cosmetic outcome as compared to traditional open surgeries.We report two such cases of rare ACC of BOT which were removed by TORS.

Case no 1:

A 55yrs male hypertensive patient presented with foreign body sensation in throat for 1month. On endoscopic examination (DL scopy), there was tumor (exophytic mass) 3x4cm involving left BOT. On CECT neck, there was enhancing thickening measuring 35x38x37mm at left BOT, left tonsil and. There was no focal lung lesion on CT scan of chest. Biopsy was reported adenoid cystic carcinoma. TORS resection of left base of tongue and left tonsil with both side neck dissection was performed . The defect was closed by pectoralis major myofascial flap (PMMF).

Case no 2:

A 27yrs male patient  presentedwith dysphagia for 3weeks.On examination (fig1), there was exophytic lesion sized 3x2cm in left BOTextending laterally to GT-sulcus, medially just crossed midline, anteriorly till circumvallate and posteriorly vallecula was not involved. On CEMRI (fig 2), lobulated enhancing mass was noted in left base of tongue sized 3.7×3.5×2.9cm crossing midline.. No cervical lymphadenopathy was noted. Incisional biopsy done under GA was reported adenoid cystic carcinoma. TORS resection of left BOT with left posterior partial glossectomy,left FOM excision and both sides neck dissections(procedure to remove neck lymph node)was done .The defect was closed by microvascular anterolateral thighmyocutaneous free flap(plastic reconstruction technique to reconstruct the tongue).

Surgical procedure:

The patient was intubated with nasotracheal tube(procedure of anesthesia).FK retractor was used for exposure of oropharynx. A tongue stich with silk was used to keep the tongue protruded. da Vinci si robot was used with upward facing 8mm 300 camera better visualization. Robotic arms were docked in the mouth. The wide area around the tumor with 1cm margin was mapped. The tumor was excised using robotic instruments, monopolar cautery spatula and Maryland bipolar forceps. In both the cases, the defect crossed midline and extended till FOM. The defects were repaired with locoregional or free flaps. The tumor specimen was sent for frozen section and accordingly margins revised to get adequate negative margin of at least 5mm. Neck dissections were performed before primary excision and left facial and lingual arteries were ligated to better hemostasis during primary excision.Temporary tracheostomy was done in both the cases because of more than 50% of base of tongue was resected.

Post-operative course:

The post-operative courses were uneventful. Tracheostomy was removed on POD5 and orally liquid diet started from POD4 which gradually changed to soft diet from POD10.Speech and swallowing assessment were performed and were found near normal without signs of aspiration. The histopathology of the tumor specimens were reported as grade II ACC pT2N0M0 with clear margin without LVI/PNI (case 1) and grade I pT3N1M0 with clear margin with PNI+(case 2). Both the patients had received adjuvant Radiation therapy with dose of 60Gy in 30 fractions. The patient continued on oral diet during and after Radiation. After one year of post-op follow up, their speech, swallowing and tongue movements are excellent with no evidence of disease.

Conclusion:

As surgery is the primary modality of treatment in adenoid cystic carcinoma, TORS should be used in resectingthese tumorsof base of tongue to achieve adequate margin and good functional outcome instead of morbid conventional surgery.