Keywords:
Endoscopy, Contrast agent-other, MR, CT, Head and neck, Metastases
Authors:
J. Cui1, S. Bhuta2; 1GOLD COAST/AU, 2SOUTHPORT/AU
DOI:
10.1594/ranzcr2014/R-0171
Methods and materials
Imaging Modalities
CT and MRI are the modalities of choice in assessing the morphology of the primary lesions and their association with adjacent structures.
Nodal involvement can also be evaluated particularly with the use of MRI.
PET imaging are also used frequently to depict nodal status and distant metastasis,
therefore has a crucial role in treatment planning when used in conjunction with other modalities.
SCC is the most common histopathological type of malignancy affecting the oropharynx and it can spread in three possible ways: 1.
local extension of the tumour over mucosal surfaces,
muscles and bones.
2.
Spread via lymphatic drainage.
3.
Invasion of the neurovascular bundle.
Evaluation of these three spread patterns is essential for accurate staging.
On CT with contrast,
large tumours are easily identifiable and often display heterogeneity due to areas of necrosis.
However,
small mucosal primaries are not well characterised and extent of infiltration is difficult to identify especially in the presence of dental artefacts,
rendering CT suboptimal in these settings.
CT still retains its value in demonstrating bone involvement and erosion,
they are displayed on bone windows as an interruption or an erosion of the hyperattenuating rim[8].
High resolution MR,
3.0T MRI scores over CT in depicting accurate localisation of primary,
infiltration and spread across the midline.
On T1 weighted MRI,
most tumours appear hypointense whereas they appear hyperintense on T2 weighted images.
With gadolinium contrast,
solid tumours will enhance and necrotic appear hypointense.
T1W images are useful in assessing the extent of the primary tumours and the spread as a result of natural contrast provided by the fat which has high signal additionally T1 W images also help in detecting neurovascular and bone marrow involvement.
One drawback of MR imaging is the possible production of suboptimal images due to motion and breathing artefacts,
tumour size can also sometimes be over-estimated in the presence of haemorrhage and inflammatory changes[1].
Higher spatial resolution offered by MRI is useful in assessment of the bone marrow involvement,
neurovascular bundle encasement,
prevertebral space involvement and perineural spread.