1-Contains fat, arteries, veins and nerves.
2-Start from the inferior border of the mandible and till reaching the skull base(axial scan).
3-Three to five mm.thickness of slice.
4-Anatomic relations
-Antero-lateral.
Where you find maxillary antrum and muscles(medial and lateral pterygoid muscles, temporalis and masseter muscle) in addition to the most important structure which is infra temporal fat present just posterior to maxillary sinus as surgeon make important interest about this area and if there is invasion to it or not as in case of maxillary sinus carcinoma. In addition to mandibular ramus and mandibular nerve branches.
-Postero-lateral.
Deep lobe of the parotid gland.
Distance between the mandible and the spine can be divided into two parts by styloid process, the distance between the mandible and styloid process is known as stylo-mandibular tunnel where the deep lobe of the parotid gland is present, while the space between the styloid process and vertebra is known as retro-styloid space where you can find internal carotid artery, internal jugular vein, cranial nerves 9-12 and sympathetic plexus in addition to lymph nodes.
Retro-mandibular vein.
Facial nerve.
External carotid artery.
And lymph nodes.
Contains carotid sheath and parotid gland.
-Medial.
Contains mucosa of the pharynx.
The pharyngeal mucosal space is separated from para pharyngeal space by the pharyngo-basilar fascia which is a tough membrane maintaining the air way patent but it could be crossed only by aggressive lesions.
Your responsibility as a radiologist is confined to know from where the lesion is coming in relation to the para-pharyngeal fat.
Is it coming from antero-lateral, postero-lateral or medial aspect.
-Medial aspect lesions:
Causing lateral displacement of the para-pharyngeal fat.
-98% of masses arising from this area are carcinomas.
80% are of squamous type.
Other are adenoid cystic and muco-epidermoid carcinomas.
-2 %Lymphoma, angiofibroma and sarcoma in children(if you find with the mass lymph nodes enlargement, this will suggest more lymphoma rather than sarcoma as the latter metastasizes through blood stream.
Nasopharygeal anatomy :
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| Contrast enhanced CT 1- Parapharyngeal space. 2- Masticator space. 3- Mucosal space. 4- Carotid space 4- Parotid space. 5 -Mucosal space. 6- Perivertebral space (anterior portion). 7- Retropharyngeal space (virtual at this level). |
The lateral wall of the nasopharynx is formed of an elevation known as torus tubarius with a posterior depression known as fossa of rusenmuller and another anterior one known as fossa of Eustachian tube.
The torus tubarius is composed of 2 muscles which are the tensor and levator villi palatine muscles, this two muscles are separated by a fat strip.This fat strip is the most earliest sign to be noted in nasopharyngeal carcinoma where it becomes destroyed, this could be only seen by MRI T1 imaging but not by CT.
Nasopharyngeal carcinoma early diagnosis:
-Should be done by MRI as the following
Obliteration of the fat strips between tensor and levator villi palatine muscles.
Obliteration of the fat space between nasopharynx and vertebrae.
Invading para pharyngeal space shifting para pharyngeal fat laterally.
Staging of nasopharyngeal carcinoma:
T1=Confined to the nasopharynx.
T2=Extension to the oropharynx(down) or nasal fossa(anterior extension).
T3=Invasion of bones or sinuses.
T4=Intra cranial, hypo pharynx or orbital extension.
Extension of the nasopharyngeal carcinoma:
Anterior: Nasal fossa, infra temporal fossa and maxillary sinus.
Posterior: Prevertebral muscles and carotid sheath.
Lateral:Prapharyngeal space and masticator space(space containing pterygoids, temporalis and masseter muscles).
Medial: to the opposite site.
Other areas of squamous cell carcinoma is oropharynx and tonsils.
Postero-lateral aspect:
Stylo-mandibular tunnel:
-Styloid process will move back with widening of stylo-mandibular tunnel.
-Most of the masses seen in the deep portion of the parotid gland are malignant.
-Para-pharyngeal fat will move medially.
Antero-lateral aspect:
-Mandibular pathology as
Adamentinoma
Chondrosarcoma which seen as a mass with calcification causing destruction of the mandible.
Mandibular osteosarcoma which characterize by sun ray speculation of peri0osteal reaction.
Mandibular metastases.
-Lesions arising from pterygoid muscle in a child could be lymphoma or rhabdomyosarcoma.
In a child, whenever is the place of the mass in nasopharynx, oropharynx or any other places you should diagnose non Hodgkin lymphoma or rhabdomyosarcoma until prove otherwise.
-Metastases.
Retro-styloid space:
-Glomus tumor(jugular) should be hyper vascular lesion giving appearance of salt and pepper appearance(here you should do selective angiography and CT angiography but do not do MRI angiography as it can not elicited it.
It cause destruction of jugular foramen.
-Lymph node enlargement---search for other lymph node enlarged in the neck.
-Neurofibroma(cystic component).
Styloid process moves anteriorly.
Benign lesions of the nasopharynx:
Tornwald's cyst:
-A mucous retention cyst occurs in the mid line nasopharynx.
-Low signal in T1 and high signal in T2WI.
Nasopharyngeal angiofibroma:
-Arises near spheno-palatine foramen.
-Almost exclusively in adolescent boys causing epistaxis.
-Very vascular lesion needs embolization before resection.
-Forward displacement of the posterior wall of the maxillary sinus, a sign known as Holman-Miller sign which is characteristic.
-Can extends within sphenoid sinus(one of character of this lesion).
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