Imaging of nasopharyngeal carcinoma ATTIA M, KOUKI S, LANDOULSI M,BOUGUERRA S,AROUSY, BOUJEMAA H, BEN ABDALLAH N. HEAD AND NECK : HN 21

INTRODUCTION  Nasopharyngeal carcinoma is a non-lymphomatous, squamous-cell carcinoma that occurs in the epithelial lining of the nasopharynx.  This neoplasm shows varying degrees of differentiation and is frequently seen at the pharyngeal recess (Rosenmüller’s fossa) posteromedial to the medial crura of the eustachian tube opening in the nasopharynx.  Many histological entities exist from Squamous Cell Carcinoma (SCC) to the more frequent Undifferentiated Carcinoma of the Nasopharyngeal Type (UCNT), and these entities share endemic areas throughout the world

 the disease occurs with much greater frequency in southern China, northern Africa, and Alaska.  While NPC may occur at any age, it has a bimodal distribution with the first peak of occurrence in the 15–25 years age range and the second peak in the fourth to fifth decade.  EBV infection is clearly associated with NPC.

 The symptomatology is variable and misleading.  The diagnosis is based on endoscopy + biopsy.  The imaging has an interest in: - The diagnosis (fossa of Rosenmüller + + +) - The staging of the tumor. - The post therapeutic surveillance.  The aims of our study are to : -Remind the normal radioanatomy. - Know the main routes of extension. - State the purpose of imaging during the post treatment monitoring.

Normal anatomy  The nasopharynx is a mucosal lined, tubular-shaped midline structure which constitutes the superior extendt of the airway.  Its cranial border is limited by the skull base(sphenoid sinus and clivus)  The posterior margin of the nasopharynx extends to the prevertebral muscles and soft tissues.  Anteriorly, the nasopharynx freely communicates with the nasal cavity through the posterior choane.  Laterally it abuts the pyramidal- shaped parapharyngeal spaces.

Normal anatomy  The rigid and tough pharyngobasilar fascia provides structural support for the nasopharynx.  The fascia forms a three-sided curtain which opens anteriorly toward the nasal cavity.  Superiorly, the fascia is fixed to the skull base from the pterygoid plates to the carotid canal.  Lateraly it is adherent to the cartilaginous portion of the eustachian tube.  It forms a closed and resistant barrier  The sinus of Morgagni is the only defect through which the eustachian tube and the levator veli palatini muscle pass.

 As a result of the close proximity of the foramen lacerum and foramen ovale to the sinus of Morgagni and eustachian tube there exists a potential pathway for the spread of disease to cranial cavity. the foramen lacerum the foramen ovale

Radioanatomy

nasopharynx T2 weighted imageT1 weighted image Rosenmuller’s fossa

Radioanatomy nasopharynx T2 weighted imageCT image

Extension pathways.  The nasopharyngeal tumor may extend straight up to the base of the skull, down to the oropharynx and to the nasal cavities forward.

Extension pathways  Lateral to the pharyngobasilar fascia, the nasopharynx is bounded by four spaces which are divided by three layers of deep cervical fascia.  These include the masticator (infratemporal fossa), the parapharyngeal, the carotid and the parotid spaces.  Lateral deviation and or infiltration of the parapharyngeal fat are sensitive indicators of the spread of nasopharyngeal disease. Dark : pharyngobasilar fascia. Blue : parapharyngeal space. Green : the masticator space. Red : the carotid space.

Imaging techniques

Computed tomography  Performing exam  Extending from the skull base to the thoracic inlet ( cervical adenopathy)  Thin slices ( 1-3mm)  intravenous contrast enhancement ( 2cc/Kg)  Advantages: Detecting bone erosion and cervical lymph node.  Limits: Analysing the peripharyngeal spaces and perinervous extension.

MRI  Technique Exploration in the three plans of the space in T1, T2 and T1 gadolinium + / - FatSat.  Advantages: - Extension to the skull base. Extension to the deep face spaces. - Perinervous and perivascular extension.  limits: Claustrophobia. Metallic components

TNM classification  T1: Tumor confined to the nasopharynx.  T2: Extension to: T2a: nasal cavity and / or oropharynx, T2b: parapharyngeal space.  T3: Extension bone and / or sinuses.  T4: intracranial extension, cranial nerves, the hypopharynx, with infratemporal fossa and / or the orbit.

TNM classification  N0: No regional metastatic ADP. N1: metastatic (s) unilateral (s) ADP (s), 6 cm, N3b: at the supraclavicular fossa.  M: M0: no metastases, M1: metastases. Distant metastases: bones, liver, lung, pleura

Results  5 patients were evaluated with MRI before and after contrast material.  10 patients with advanced stages had CT tomgrpahy with intravenous contrast enhancement.  MRI is most efficient for local staging especially in stage 1 and 2 (TNM classification) which correspond to 5 patients in our study.  Computed tomography is performing to determinate bone extension and metastatic locations (liver, lung…) in 10 patients with advanced stage tumors.

T1 tumor Blunning of left fossa of Rosenmuller and enlargement of levator palatini muscle

T2a tumor nasopharyngeal tumor with oropharyngeal extension

T2b tumor nasopharyngeal tumor with parapharyngeal extension throuugh pharyngobasilar fascia

T4 tumor nasopharyngeal tumor with infratemporal fossa extension

T4 tumor Coronal computed tomography showing bony involvement of the sphenoid sinus and intracranial extension

DISCUSSION  Computed tomography and MRI have respective specific advantages and disadvantages.  MR seems to provide a more accurate evaluation of the extent of the primary tumor; in fact, MR is able to identify as retropharyngeal nodes findings previously misdiagnosed on CT as oropharyngeal or parapharyngeal invasion.  Moreover, it provides new pieces of information such as the infiltration of long muscles of the neck and pterygoid muscles that, in most cases, cannot be clearly imaged with CT; according to some authors, MR can also detect cavernous sinus and early perineural invasion.

DISCUSSION  The advantages of CT over MR in imaging bone details, especially when the bone contains little or no fat marrow, are well known.  This suggests that CT should continue to be part of the pretherapeutic workup whenever the base of skull involvement is suspected or possible, but not clearly detected with MR. In fact, upstaging leads to a substantial change of treatment volume and may hint that a locally aggressive treatment should be delivered.  As far as follow-up is concerned, the basic clinical question of differentiating between postradiation changes and recurring tumor seems to be less often uncertain with MR than with CT.  Therefore, MR, even if not a panacea, may be the preferred modality. However, the cases with subtle bone erosions or cortical defects on staging CT are probably best followed up with this modality.

DISCUSSION  FOLOW UP MRI + +: once a year during 5 years and then every 5 years  Goals: - evaluate tumor response to treatment - Tracking early recurrence (T4: 60% recurrence at 10 years) -Guiding biopsies

Conclusion  The imaging constitutes a key element in the diagnostic and therapeutic care of the nasopharyngeal carcinoma.  It aims at determining exactly the point of departure and the extension of the tumor in order to establish the classification: tumor-nodes-metastases and to specify the fields of the irradiation.

References  Staging and follow-up of nasopharyngeal carcinoma: magnetic resonance imaging versus computerized tomography. Patrizia Olmi and al. Int. J. Radiation Oncology Biol. Phys., Vol. 32, No. 3, pp ,  Bilan d’extension d’une tumeur du nasopharynx. F Dubrulle. Journées françaises de radiologie  Cancer du nasopharynx. F Cohen, O Monnet, F Casalonga, A Jacquier, V Vidal, JM Bartoli et G Moulin. J Radiol 2008;89:  Current understanding and management of nasopharyngeal carcinoma. Tomokazu Yoshizaki and al. Auris Nasus Larynx 39 (2012) 137–144