Type:
Educational Exhibit
Keywords:
Diagnostic procedure, MR, CT, Head and neck, Cancer
Authors:
I. Ben Amara1, S. Esseghaier2, R. Aouini3, M. Bouzrara4, N. REGAYA5, A. Zidi3; 1Tunis, tunis/TN, 2menzah 7/TN, 3Tunis/TN, 4Ariana/TN, 5megrine/TN
DOI:
10.1594/ecr2018/C-2292
Findings and procedure details
Detection of NPC :
In patients with high risk of NPC (elevated blood serology),
an endoscopic guided biopsy isperformed to sample the nasopharynx even when the endoscopy is normal.
MR is a valuable tool to detect small tumors that would aid in directing the site of biopsies and avoid to miss small mucosal lesions (6% of tumors not seen on endoscopy).
Staging of NPC :
It is important to understand the potential patterns of tumor spread in NPC to anticipate and detect subtle findings which may upstage a tumor and lead to change therapy.
The seventh edition of the AJCC2010,
brought important simplifications of the prior system.
T category :
Assess the relationship of the primary tumor to adjacent structures.
The spread of the tumor is more likely submucosal through the pharyngobasilar fascia into the deep spaces of the neck.The mucosal spread of the NPC is more likely superior to the skull base than inferior to the oropharynx.
- T1 : Tumor confined to the nasopharynx,
oropharynx,
or nasal fossa.
There is no spread to the parapharyngeal space.
NPC most often arises in the fossa of Rosenmuller Fig. 3 .Unilateral serous otitis or the observation of unilateral middle or mastoid fluid maybe the only manifestation requiring more investigations to diagnose small recessus tumors Fig. 4 .Tumors extending to the oropharynx or nasal cavity (previously staged as T2a) have not a worse prognosis than tumors confined to the nasopharynx staged now as T1.
-
T2:Tumor extends to parapharyngeal space with posterolaterally spread through the levatorpalatini muscle and pharyngobasilar fascia to the parapharyngeal fat Fig. 5 .The spread to the parapharyngeal space increases the risk of distant metastases and tumor recurrence,
it may involve the carotidien space, and lead to middle ear and mastoid effusion by compression of the eustachian tube.
In case of retropharyngeal spread the tumor is stillstaged T2,
although the invasion of this region containing lymphatics and venous plexus,
increases the risk of distant metastases Fig. 6
- T3 : Tumor invades bony structures of the skull base or paranasal sinuses Fig. 8 Fig. 9 .Bones most commonly invaded are: clivus Fig. 7 ,
body of the sphenoid Fig. 10 ,
pterygoid bones,
the petrous temporal bones .
The T1 weighted offer a good contrast to assess the extent of the tumor to skull base.
CT may be also a good tool to reveal permeative or erosive bone lesions of the skull base,
sclerosis of pterygoid bone, or spread along foraminal pathways. Radiologist should depict the invasion of skull base foramina : foramen oval Fig. 11, foramen lacerum Fig. 13 , foramen rotondum Fig. 14 vidian canal Fig. 15, pterygomaxillary and petroclival fissures. The extension to the pterygopalatine fissure provides a route of spread to : the orbit, the infratemporal fossa,
nasal cavity and middle cranial fossa. Invasion of the hypoglossal nerve canal and jugular foramen may be observed Fig. 16
-
T4 : Tumorwith :
- Intracranial extension : Direct invasion of the brain is rare Fig. 17 .
Meningeal invasion appears as nodular enhancement,
often posterior to the clivus or in the middle cranial fossa Fig. 18 .
The cavernous sinus may be involved with many ways :from the carotide canal ,
foramen ovale Fig. 19 ,
orbital fissures , or directly through the skull base Fig. 20 Fig. 21 .
- Involvement of cranial nerves : perineural tumor spread is an insidious and it may progress upward and backward to the cavernous sinus and middle cranial fossa through nerves foramina.
It invades cranial nerves from II to VI and IX ,XI and XII Fig. 16 and cervical sympathetic nerves.
Maxillary,
mandibular and hypogloss nerves are the most commonly involved.
MR findings in case of perineural spaces are not consistent seen on gadolinium-enhanced T1-weighted images : obliteration of the neural fat pads adjacent to the neurovascular foramina and enlargement or abnormalenhancement of the nerve.
- Masticator space invasion : Tumors extend laterally from the parapharyngeal space to the infratemporal fossa Fig. 22 .
It may progress through the pterygoid base,
or the pterygomaxillary fissure.
It invades medial and lateral pterygoid muscles and temporalis muscle.
- Orbit : Orbital invasion is rare,the orbit can be invaded directly or via the inferior orbital fissure and superior orbital fissure Fig. 24 .
The extension to the pterygopalatine fissure provides a route of spread to the orbit Fig. 25
- hypopharynx invasion : The hypopharynx is very rarely involved at diagnosis.
N category :
We were based on the shortest diameter to diagnose nodal metastases. A group of three or more nodes,
necrosis or extracapsular spread are prognostic factor (>5 mm in the lateral retropharyngeal region, >11 mm in the jugulodigastric region > 10 mm in other non retropharyngeal nodes of the neck)
N1 : Retropharyngeal lymphnode (unilateral or bilateral) .MRI is a good tool to separate the lateral retropharyngeal nodes from the primary tumor.Retropharyngeal nodes are the first echelon of metastatic spread Fig. 26
N2 : Unilateral metastasis in lymphnodes,
≤ 6 cm in greatest dimension,
above supraclavicular fossa
N3 : Bilateral metastasis in lymphnodes,
≤ 6 cm in greatest dimension,
above supraclavicular fossa .
N4 : Metastasis in lymphnodes> 6 cm in dimension or in the supraclavicular fossa.
M category
Distant metastases are common in NPC.
The most common sites of metastases are bone ,lung and liver.
M0 : No distant metastasis.
M1 : Distant metastasis.