Paraph Imaging

8/7/2019 Paraph Imaging

http://slidepdf.com/reader/full/paraph-imaging 1/20

Role of imaging in the diagnosis of parapharyngeal space and adjacent space

lesions

Dr T Balasubramanian

Drtbalu's otolaryngology online

http://www.drtbalu.co.in/




Introduction:

Parapharyngeal space is a suprahyoid neck space. It is surrounded by other importantfacial spaces. Old text books divided this space into prestyloid and post stymoid

compartments. The prestyloid compartment lying infront of the styloid process and

the post styloid one lying behind it. Current literature designates post styloid

compartment as carotid space and the prestyloid compartment is considered to be the

true parapharyngeal space. The parapharyngeal space contains fat. This is clearly

visible in imaging and displacement of fat indirectly helps the radiologist to identify

and quantify the extent of lesions involving parapharyngeal space. Parapharyngeal

space is a hidden area that cannot be easily examined. Lesions of this space present

rather late and in advanced stage. A surgeon will have to resort to imaging in order tovisualize this area.

Anatomy:

Anatomically parapharyngeal space could be considered as a cone shaped space

extending from the skull base above and hyoid bone below on either side of pharynx.






Anatomically the carotid space (poststyloid space) is separated from the

parapharyngeal space proper (prestyloid space) by the tensor-vascular-styloid fasciawhich overlies the tensor veli palatini muscle. Benign tumors involving this space is

likely to remain confined to the space.

Boundaries of parapharyngeal space:

Superior:

Portion of the temporal bone lateral to the attachment of pharyngobasilar fascia and

medial to the foramen ovale and foramen spinosum. None of the foramina of the

skull base are involved in the formation of superior boundary of parapharyngealspace.

Inferior:

Greater cornu of hyoid bone

Posterior belly of digastric muscle

At this level the parapharyngeal space blends with the posterior part of

submandibular space

Medial:

Buccopharyngeal fascia

Pharyngobasilar fascia

Pharyngeal constrictors

Lateral:

Fascia covering the pterygoid muscles and sphenomandibular ligament.

Parotid space communicates with parapharyngeal space laterally through thestylomandibular tunnel. The stylomandibular tunnel is surrounded / enclosed by the

stylomandibular ligament. The stylomandibular ligament extends from the styloid

process to the angle of the mandible.

Anterior:

The pterygomandibular raphe. This raphe extends from the hamulus of the medial

pterygoid plate to the posterior aspect of the mylohyoid line on the lingual surface of

the mandible






Posterior:

The tensor vascular styloid fascia which overlies the tensor veli palatini muscle. This

fascia extends from the medial pterygoid plate to the styloid process.

The anatomical location of the parapharyngeal space is rather unique. It is locatedcentrally in relation to the surrounding neck spaces. The fat content of this space

gives a unique appearance on CT / MRI. Primary lesions involving the

parapharyngeal space is very rare but the displacement pattern of the fat in this space

due to lesions involving other neck spaces could be an excellent indicator for the

origin of the lesion.

Diagramatic representation of parapharyngeal space and its relations






Axial T1 weighted MR image showing normal radiological anatomy of

parapharyngeal space.

Asterix – Fat planePMS – Pharyngeal mucosal space

MS – Masticator space

PS – Parotid space

ICA – Internal carotid artery

IJV – Internal jugular vein






Illustration showing tumor involving the pharyngeal mucosal space displacing the

parapharyngeal space pad of fat inferiorly. This displacement can be clearly seen inCT / MRI imaging.






Axial CT contrast showing pharyngeal mass pushing the parapharyngeal space

postero laterally with obliteration of the normal fat plane seen in the parapharyngeal

space.






Diagram showing

tumors/lesions of

masseteric space causing

compression of the

parapharyngeal space

pushing in posteromedially.






CT scan axial cut showing masseteric mass pushing the parapharyngeal space

posteromedially

Figure showing parotid tumor growing inwards and pushes the parapharyngeal space

anteromedially. It usually displaces the tonsil / lateral pharyngeal wall medially.






Parotid mass seen pushing the parapharyngeal space medially. Note the pad of fat is

also obliterated. This is a contrast axial CT showing the great vessels (2,3).

Diagram showing carotid space tumor pushing the parapharyngeal space

anterolaterally.






Axial contrast CT showing enhancing mass involving the carotid space pushing the

parapharyngeal space anteromedially. Note the obliteration of fat plane.

Pharyngeal mucosal space:

This space include the nasopharyngeal and oropharyngeal mucosal lining. This space

is lined on the outside by the pharyngeal constrictors and lined on the inside by

squamous epithelium. This space contains minor salivary glands and lymphoid tissue

of the waldayer's ring.

Pharyngeal mucosal space lesions include:

1. Squamous cell carcinoma

2. Tumors involving minor salivary glands

3. Lymphoma4. Sarcoma

Masticator space:

This space extends from the skull base to the inferior border of the mandible. This

space is enclosed between the split layers of the superficial layer of the deep cervical

fascia.

Contents of this space include:






1. Ascending ramus of mandible

2. Posterior body of mandible

3. Muscles of mastication (masseter, medial and lateral pterygoids and

temporalis)

4. Motor and sensory branches of mandibular division of trigeminal nerve

5. Inferior alveolar artery and vein

The Masseteric space extends superolaterally along the lateral surface of the

temporalis muscle. This portion of the masseteric space is divided into superior and

inferior portions by the presence of zygoma. Anteriorly this space continues with

that of the buccal space. There is ofcourse no facial boundary between these two

spaces and infections can freely traverse between these spaces. The parapharyngeal

space is located postero medial to the masseteric space, hence lesions involving this

space tends to displace the parapharyngeal pad of fat posteromedially.






Axial CT neck showing masseteric abscess (1) pushing the parapharyngeal pad of fat

posteromedially (**)

Malignant tumors involving the mucosal lining of adjoining spaces (oral cavity,

oropharynx and maxillary sinus) frequently invade this space causing trismus due to

involvement of muscles of mastication. This is true for all malignant lesions except

lymphoma. Lymphoma doesn't cause trismus even when masseter muscle is

infiltrated by the tumor cells. Imaging can also help to pinpoint involvement of this

space even before development of trismus. Trismus is infact a late stage of malignant

infiltration of this space. Involvement of this space by malignant tumors puts

mandibular division of trigeminal nerve at risk. Adenocystic carcinoma involving

this space may spread along this nerve. Imaging doesn't clearly reveal perineuralspread of tumors involving mandibular division of trigeminal nerve. Indirect signs of

nerve involvement like thickening of the nerve / enlargement of foramen ovale can be

sought. Enlargement of foramen ovale can be seen only in the bone window cuts of

CT scan. Primary tumors involving this space is rather rare. But tumors involving

this space in paediatric age group should prompt a diagnosis of rhabdomyosarcoma

unless proved otherwise.






Axial CT showing foramen ovale (green arrow) and foramen rotundum (red arrow)

Axial CT (Bone window) showing normal and enlarged foramen ovale






Axial CT scan showing soft tissue mass in the masseteric space.

(Rhabdomyosarcoma)

Common lesions involving the masseteric space:

Inflammatory / infective lesions – odontogenic infections, cellulitis, abscess and

myositis

Congenital – Hemangioma, lymphoid malformation.

Neoplastic – Benign tumors involving muscle / bone

Malignant tumors – Rhabdomyosarcoma, osteosarcoma, osteosarcoma, metastatictumors.

Parotid space:

This space lies posterolateral to parapharyngeal space. In this space the superficial

layer of deep cervical fascia splits to enclose this space. The most important content

of this space is the parotid gland. The facial nerve divides the gland into superficial

and deep lobes. The parotid gland becomes encapsulated very late in its development

and this is the reason for the presence of intraparotid lymph nodes.

Most common lesions involving this space are lesions involving the superficial lobe

of parotid gland. Deep lobe of the parotid gland are involved very rarely. The

position of the facial nerve in the parotid gland can be studied by looking for the

retromandibular vein in the CT image of parotid gland. The facial nerve lies lateral to

this vein.






Contrast Axial CT showing malignant tumor involving the right masseteric space.

Axial CT showing mass involving the superficial lobe of parotid gland






Axial CT scan showing mass involving the deep lobe of parotid gland

Common lesions involving the deep lobe of parotid gland are mostly benign.

Pleomorphic adenoma is the commonest. Tumors involving the deep lobe of parotid

gland displaces the parapharyngeal space postero medially. Pleomorphic adenomas

involving the parotid gland lights up bright in T2 weighted MRI images. The

intensity of these lesions in T2 weighted images matches that of CSF fluid. This is

the reason why MRI is the preferred imaging modality in ruling out recurrent tumors

after successful excision of pleomorphic adenomas involving parotid gland. Other

tumors that light up bright in T2 weighted MRI are lymphangioma, hemangioma and

mucoepidermoid carcinomas.

Lesions involving the parotid space include:

Neoplasms:

Pleomorphic adenoma

Warthin tumor

Lipoma

Mucoepidermoid carcinoma

Adenoid cystic carcinoma

Squamous cell carcinoma

Hodgkin's lymphoma






Inflammatory lesions:

Parotitis / abscess

Reactive lymphadenopathy

Lymphoepithelial cysts

Congenital:

Hemangioma

Venous malformation

Lymphatic malformationCysts involving first branchial cleft

Carotid space:

This contains the carotid sheath. All three layers of deep cervical fascia contributes

to its formation. This space spans the entire neck from the skull base to the arch of

the aorta. The carotid space lies posterior to the parapharyngeal space.

Contents of this space include:

Carotid artery

Internal jugular vein

Cranial nerves 9,10,11 and 12. The vagus nerve lies posterior and lateral to the

carotid artery.

Sympathetic chain lies posterior and lateral to the carotid artery.

The precise anatomical relationships of the structures of carotid sheath really helps in

discerning the precise anatomical origin of lesion in the carotid sheath. Vascular and

neurogenic tumors are the most common lesions involving this space. Normal

variations involving the internal jugular vein (dominant) or tortuous internal carotid

artery can be mistaken for lesions if contiguous imaging sections involving this areahas not been examined.

Tumors involving the suprahyoid portion of carotid sheath pushes the parapharyngeal

pad of fat anteriorly, the internal carotid artery gets displaced anteriorly and the

internal jugular vein gets displaced laterally.

Most common benign soft tissue tumors involving this space are paragangliomas and

nerve sheath tumors. These tumors are usually asymtomatic and are incidental

discoveries during imaging made for unrelated problems. Imaging helps in discering






paragangliomas from nerve sheath tumors. Paragangliomas are very vascular tumors

and are known to arise:

1. At the bifurcation of common carotid artery (carotid body tumors)

2. At the perineurium of vagus nerve (glomus vagale)

3. From the jugular bulb (glomus jugulare)

4. In the middle ear cavity (glomus jugulare)

Among these four lesions only glomus jugulare and glomus vagale are intimately

related to the parapharyngeal space. These lesions enhance on contrast CT / MRI and

also demonstrate flow voids. Flow voids in MRI are virtually diagnostic of

paraganglioma but it would be apparant only if the tumor is more than 2 cm in

diameter.

Classically carotid body tumor is located at the bifurcation of the carotid artery in the

infrahyoid portion of neck. It splays the internal and external carotid arteries. Thiscan be clearly visualised in contrast imaging modalities.

Common lesions involving carotid space include:

Neoplastic:

Paraganglioma

Schwannoma

Meningioma

Direct extension of cervical node metastasis

Vascular:

Internal jugular vein thrombosis

Carotid artery thrombosis

Carotid artery aneurysm, pseudoaneurysm

Inflammatory:

Abscesses

Radiological distinction between schwannomas and neurofibromas:

This is not easy. Heterogenous lesions commonly present in schwannomas. This is

due to cystic change / haemorrhage which are commonly seen in schwannomas.

Schwannomas are well encapsulated tumors arising from the schwann cells of the

peripheral nerve sheath. The vagus nerve and the sympathetic chain are the common

sites of origin. Schwannomas don't demonstrate flow voids in MRI even when the

lesions are large. Schwannomas when present close to the skull base can cause

regressive remodelling of bone, this type of remodelling is not seen in






paragangliomas.

Axial contrast CT neck showing carotid body tumor.

Spread of malignant secondary deposits from cervical nodes to the carotid sheath iscommon. Infiltration of the carotid artery by the tumor means unresectability. This

can be studied by contrast imaging which clearly demonstrates invasion of the carotid

arterial wall by the tumor.




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Paraph Imaging