Three questions decide the operation: which lobe, where is the facial nerve, and does the signal behave like a benign tumour or a malignant one.
Orient first
- The FACIAL NERVE is the surgical issue. It is not directly visible on routine sequences, so its plane is inferred from the retromandibular vein, which runs just deep to it — a mass deep to the vein is deep-lobe.
- Superficial versus deep lobe determines whether a superficial parotidectomy suffices, so stating it is the report's primary job.
- LOW T2 signal in a parotid mass is a warning sign. Most benign lesions — pleomorphic adenoma classically — are markedly T2-BRIGHT, so a solid mass that is T2-dark raises malignancy or a highly cellular tumour.
- Warthin tumour is often multiple and bilateral, and is strongly associated with smoking — bilaterality is itself a useful discriminator.
- PERINEURAL SPREAD along the facial nerve and the auriculotemporal nerve is what MRI adds over every other modality, and it changes the surgical field entirely.
Acquire the study
- High-resolution T1 and T2 in axial and coronal planes, with fat-suppressed T2 or STIR.
- Post-gadolinium fat-suppressed T1 in at least two planes, extended to the skull base to assess perineural spread.
- DWI with ADC; low ADC supports a cellular, potentially malignant lesion.
- Non-fat-suppressed T1 is essential — normal fat planes are bright and their loss is the sign of infiltration.
The manoeuvre
- Confirm which sequence you are on before judging any signal — see the MRI sequence primer.
- Locate the mass relative to the RETROMANDIBULAR VEIN and state superficial or deep lobe.
- Describe T1 and T2 signal, specifically noting whether a solid component is T2-dark.
- Assess the MARGIN: well-defined and encapsulated versus infiltrative — the strongest morphological discriminator.
- Review DWI and the ADC map.
- Assess post-contrast enhancement pattern and homogeneity.
- Follow the facial nerve course and the skull base foramina for PERINEURAL enhancement or thickening.
- Assess for extraparotid extension, skin involvement, and cervical nodes.
- Note whether the lesion is single or multiple, and whether the other parotid is involved.
What confirms it
- A well-defined, markedly T2-bright, encapsulated mass in the superficial lobe is characteristic of a pleomorphic adenoma — though tissue remains the arbiter.
- An infiltrative margin, low T2 signal, low ADC, perineural spread or nodal disease together indicate malignancy.
What licenses you to exclude it
- ⚠️ MRI STRATIFIES; IT DOES NOT EXCLUDE MALIGNANCY. A benign-appearing parotid mass still needs cytology or excision — the report should say so rather than reassuring.
- Absence of visible perineural spread does not exclude microscopic spread.
The classic misread
- Not stating the lobe, which is the one thing the surgeon needs.
- Reassuring on a T2-bright appearance without noting that tissue diagnosis is still required.
- Missing perineural spread by not imaging to the skull base.
- Judging fat-plane loss on fat-suppressed sequences, where normal fat is already dark.