Depth of invasion (DOI) now sets the T-stage for oral tongue and floor of mouth, alongside mandibular invasion, extrinsic muscle and neurovascular involvement — and the nodes, where extranodal extension changes N-stage.
Orient first
- Oral cavity SCC is common in India (tobacco, betel quid); gingivobuccal cancers involve the mandible early.
- DOI thresholds (5 and 10 mm) define the early T-stages in AJCC 8th (verify the current edition).
- Mandibular cortical erosion by gingival cancer changes surgery (marginal vs segmental mandibulectomy).
Acquire the study
- Axial and coronal T1, T2, DWI, post-gadolinium fat-saturated T1, 3 mm.
The manoeuvre
- Coronal post-contrast T1 or T2: tumour thickness and DOI in mm from the mucosal line.
- Floor of mouth, midline (lingual septum) crossing, sublingual space.
- T1: marrow signal loss in the mandible (medullary invasion).
- Perineural spread along the inferior alveolar and lingual nerves.
- Nodes: levels I–III; necrosis and extranodal extension.
What confirms it
- Biopsy-proven SCC with imaging T and N stage stated by edition.
What licenses you to exclude it
- An intact mandibular cortex on CT and normal marrow on MRI exclude bone invasion on imaging.
The classic misread
- Overestimating DOI from peritumoural oedema on T2.