“Deep extrinsic Muscle Involvement” is a Fallacy in the American Joint Committee on Cancer 7th Edition Tumor staging of the oral cavity cancers

Publication date: Available online 10 June 2017
Source:Journal of Oral and Maxillofacial Surgery
Author(s): Samskruthi P. Murthy, Krishnakumar Thankappan, Sandya Chirukandath Jayasankaran, Karippaliyil Milind, Chaya Prasad, Deepak Balasubramanian, Subramania Iyer
PurposeThe T staging in the 7^th edition, American Joint Committee on Cancer (AJCC) includes extrinsic muscle involvement to define T4a tongue carcinomas. The anatomical location of the extrinsic muscles predisposes them for early involvement even in superficial tumours. The purpose of this paper was to bring out a fallacy in this staging system, with regards to the extrinsic muscle involvement.Materials and methodsProspective cohort study of 87 oral tongue squamous cell carcinoma patients. MRI parameters, namely, 1) distance of the extrinsic muscles from the surface measured on the normal side in mm (range, mean and standard deviation). 2) maximum transverse, cranio-caudal and antero-posterior tumour dimensions (range, mean and standard deviation).3) tumor involvement of the muscles recorded on the involved side, in terms of number and percentage of each muscle involved. Histopathological depth of invasion was also recorded.Results67 patients were male and 20 patients were female. Age of the patients ranged between 18-74 years with mean age of cohort being 51 years. The mean distance of the most superficial part of muscle to the normal surface on MRI for genioglossus (antero-ventral), hyoglossus, styloglossus was 3.98, 2.13 and 0.66, respectively. The pattern of involvement of extrinsic muscle involvement showed hyoglossus, styloglossus and genioglossus involvement in 79 (90.8%), 58 (66.76%) and 31 (35.6%), respectively. In patients with pathological depth of invasion less than 10mm, involvement of hyoglossus, styloglossus and genioglossus was seen in 80, 35, and 15 %, respectively.ConclusionThe extrinsic muscles of the tongue are not deep. Even superficial thin tumors can involve the muscles. AJCC 8^th edition which has considered the tumor thickness into the staging system is in the process of being implemented. This present study would be one that will justify the removal of the extrinsic muscle involvement in defining the T4 stage of oral cavity.



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