Background and purpose: Adenoid cystic carcinoma (ACC) is a rare malignant tumor arising from salivary glands. This study aimed to evaluate the value of magnetic resonance imaging (MRI) in diagnosing ACC of the head and neck. Methods: The clinical and MRI data of 26 patients treated in Shanghai Proton and Heavy Ion Center from May 2015 to September 2017 with ACC of the head and neck (primary 19 cases

recurrent 7 cases) confirmed by histopathology were analyzed retrospectively. Results: Tumors were located in the nasopharynx (8 cases)

the palate (6 cases)

nasal cavity (4 cases)

maxillary sinus (3 cases)

submandibular gland (2 cases)

the tongue (2 cases) and the larynx (1 cases). Twenty-three lesions were irregular in shape and ill defined

and 3 lesions were oval and well defined. Compared with muscle signal intensity on MRI

all tumors demonstrated isointensity on T1WI

high or slightly high intensity on T2WI

and avid enhancement after contrast administration. We found perineural spread in 17 cases (pterygopalatine fossa involved in 16 cases

cavernous sinus in 10 cases

foramen ovale in 8 cases

foramen rotundum in 4 cases

superior orbital fissure in 2 cases

optic canal in 2 cases

hypoglossal canal in 2 cases

pterygoid canal in 1 case)

bone abnormality in 21 cases

and intracranial extension in 11 cases. Conclusion: MRI could display the extent and perineural spread of ACC in the head and neck

providing more information for treatment plan.