eRadiograph Volume 7: Imaging of Oral Cavity | Page 166

drainage. The patient presents with serous otitis, unilateral mastoid fluid. Routes of
spread of NPC are - anteriorly may grow into choanae or inferiorly through lateral walls
of pharynx or posterior tonsillar pillars into oropharynx. Laterally may push through the
pharyngiobasilar fascia to invade the parapharyngeal space. Superiorly to the skull
base. This is seen as bone destruction on CT around the clivus, foramen magnum,
middle cranial fossa, sphenoid sinus, jugular foramen with associated soft tissue.
Posteriorly into the retropharyngeal space towards the prevertebral muscles. Once the
retropharyngeal space is entered there is a high risk of distant metastases due to
extensive lymphatics, venous plexus in the retropharyngeal space. From the
parapharyngeal space can extend anterolateraly towards masticator space. Perineurial
spread to skull base - can occur from retropharyngeal via multiple foramina. or
Involvement of 5th cranial nerve- nerve of ptyergoid canal. Because of the small and
infiltrative nature of these tumors, it is important to visualise any fat plane obliteration
or loss of muscular margins as these are useful indicators of soft tissue infiltration. Fat
planes between tensor/ levator palatine muscles denoting parapharyngeal extension
and between nasopharyngeal mucosa and longus coli complex to denote
retropharyngeal extension are important fat planes to observe.

Post Treatment Appearances
Since most patients are treated with radiation or a combination of chemoradiation – a
base line MRI is obtained 2 – 3 months after therapy to evaluate response as well as
serve as a baseline to detect future recurrences. The appearances of a post treatment
imaging study are important to recognise as post treatment changes and recurrent
neoplasm should not be confused and vice versa. The post treatment scan usually
demonstrates considerable regression in size of mass lesion. There may be residual soft
tissue due to granulation tissue or fibrosis. Effects of radiation may be seen on the
calvarium–the red marrow of the calvarium is converted to yellow marrow by
radiation. This appears as hyperintensity on T1W1. If there is neoplasm involving the
skull base, following radiation this region turns hypointense on T1W, hyperintense on
T2W1 and may enhance. Enhancing soft tissue can also represent scar tissue.
Recurrent neoplasm will be seen as bony destruction with associated soft tissue,
occasionally there may be confusion with osteoradionecrosis or radiation induced
muscle inflammation.
There is usually a demarcation of the margin of the radiation field. A complication seen
with traditional radiation methods is temporal lobe necrosis–this occurs 12 – 15
months after treatment but can occur upto 5 years later. Radiation necrosis needs to be
differentiated from neoplastic spread.  It appears as ill defined white matter
hyperintensity with enhancement. MR spectroscopy will not reveal a choline peak
confirming the diagnosis.

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Pharyngeal Mucosal Space

Nasopharyngeal carcinomas have a strong tendency for metastatic spread to bone,
lung, liver – 5 % of NPC at presentation have metastases.