An approach to evaluating the post treatment imaging appearances of head and neck cancers
Dr A Madhavan, Dr K Bhatia, Dr S Mathur
Department of Neuroradiology, Lancashire Teaching Hospitals NHS Foundation Trust
Head and neck cancers affect approximately half a million patients a year worldwide1. Treatment is dependent on stage of disease at diagnosis and includes surgery and chemoradiotherapy, often used in combination. Surveillance imaging is initially commenced 3 months post treatment. Aims of imaging surveillance are:
to evaluate treatment response
to assess residual or recurrent disease and complications.
Imaging is challenging to evaluate due to distorted anatomy post surgery and radiotherapy2. Differentiating expected post treatment changes from disease recurrence and complications is crucial as it can alter patient management.
Purpose : Provide a CT/MR imaging overview of treatment response, expected post treatment changes and illustrate some complications that can occur.
TYPES OF NECK DISSECTION
Radical (RND) : removal of all ipsilateral cervical lymph node groups I to V from inferior border of mandible to clavicle & non-lymphatic structures
Sternocleidomastoid, Internal jugular vein (IJV) , Spinal accessory nerve (SAN)
Modified Radical (MND)
-Spares 1 or more of above non-lymphatic structures
-Spares all above
Extended neck: Radical + removal of additional nodes (level VI and VII) +/- vagus nerve, hypoglossal nerve etc
Selective neck dissection
-Marked decrease in deep cervical fat is common.
-Posterior & medial displacement and distortion of SCM. Atrophy maybe seen.
-Submandibular gland absent if Level 1 nodes resected
Flap reconstruction performed to close surgical defect during curative resection either pedicle or free flap used. Flaps are composed of muscular and fatty components. MR images below demonstrate appearances post flap reconstruction.
Assessment of treatment response
Key MR imaging sequences:
-Primary site – Axial T2, DWI
-Nodes – Axial T2 and DWI
-Post-contrast fat suppressed T1
Assessment of treatment response
Treatment response post chemoradiotherapy can be assessed early as 6 weeks on MR: T2 signal change of residual can be correlated with likelihood of tumour3. Three groups:
- hypointense T2 signal and volume loss (low, good local control)
- mixed features (indeterminate)
- intermediate T2 signal same as initial tumour with no volume loss (high, local failure)
DWI is a very useful tool to assess tumour response & recurrence. High signal intensity with low ADC values is highly suspicious for tumour. Right tonsillar mass on axial T2 demonstrating marked volume reduction and T2 hypointense signal change post radiotherapy in keeping with tumour response. Also note resolution of high signal intensity on DWI.
Can be at primary site/adjacent to flap or nodal recurrence; typically 2 years post treatment. Enhancement of recurrence typically ill-defined (vs striated enhancement of flap) as shown on MR image on left. Contrast CT images demonstrate recurrence deep to fatty flap and necrotic nodal recurrence.
Post radiation changes
Effect of radiotherapy on soft tissues and salivary gland can range from reticulation of subcutaneous tissue, mucosal/retropharyngeal oedema in early stages to salivary gland atrophy in the late stages.
Below are few examples of complications more specific to post head and neck cancer treatment:
-Post neck dissection chylous fistula: Due to thoracic duct injury, typically when level IV nodes are dissected.
-Cranial nerve denervation: trigeminal, spinal accessory and hypoglossal nerves are especially at risk.
-Osteonecrosis: Adjacent irradiated bone becomes weakened/undergoes destruction. Occurs 1- 3 years post radiotherapy.
-Radiation necrosis of adjacent brain parenchyma
Interpretation of post treatment head and neck imaging involves a thorough understanding of post-operative anatomy, patterns of tumour recurrence and expected post-radiotherapy changes. Awareness of the more specific complications relating to head and neck cancer treatment is also crucial. There is an increasing use of a multimodality approach to problem solving in these cases with PET-CT and ultrasound being important adjuncts to CT and MR imaging.