Indian Journal of Radiology and Imaging Indian Journal of Radiology and Imaging

HEAD AND NECK
Year
: 2005  |  Volume : 15  |  Issue : 1  |  Page : 41--46

Pictorial assay - parapharyngeal space lession


S Biswas, S Saha, A Sadhu 
 Department Of Ent. Department Of Ct & Mri Medical College, Kolkata, 88, College Street, Kolkata- 700073., India

Correspondence Address:
S Saha
Sundaram Apartment, 91, Sarat Chatterjee Road Borat, Lake Town Kolkata-700089.
India




How to cite this article:
Biswas S, Saha S, Sadhu A. Pictorial assay - parapharyngeal space lession.Indian J Radiol Imaging 2005;15:41-46


How to cite this URL:
Biswas S, Saha S, Sadhu A. Pictorial assay - parapharyngeal space lession. Indian J Radiol Imaging [serial online] 2005 [cited 2019 Oct 20 ];15:41-46
Available from: http://www.ijri.org/text.asp?2005/15/1/41/28742


Full Text

Parapharyngeal space is a fascial space that extends from skull base to hyoid bone, and forms the neurovascular conduit to head. Tumors may arise from the individual components of the space or may invade from the surrounding structures. In the era of antibiotics, infection and abscess formation in the space has significantly come down.

 EPIDEMIOLOGY



-- World literature suggests that parapharyngeal space lesion accounts for around 0.5% of all head & neck tumors [1]. Of these pleomorphic adenoma is the commonest pathology [2]. For carotid body tumors there is slight female predominance. Parapharyngeal space infection is now a less common entity. With advent of modern antibiotics it now accounts for only 30% of deep neck infections [3].

 ANATOMY



The parapharyngeal space is divided in three main compartments, being prestyloid ,post styloid (comprising carotid space) and retropharyngeal space. Deep lobe of parotid gland comes in lateral relation of the space and frequently its tumor may invade the space [Figure 1]. Carotid space is comprised of carotid artery, IXth, Xth & XIIth nerves, cervical sympathetic chain. Retropharyngeal space contains lymph node that is present mainly during childhood. Within carotid space, carotid body measuring 3-6mm, ovoid in shape and located on to posteromedial aspect of common carotid artery near bifurcation, is seat to a type of paragangliomas called carotid body tumor [Figure 2].

 PATHOLOGY



Commonest type of tumor in parapharyngeal space is pleomorphic adenoma that may rise either from minor salivary gland or from deep lobe of parotid. Next is the neurogenic tumors accounting for 17% to 25% of parapharyngeal tumors [2]. Where as neurofibroma may disturb nerve function, by pressing on it, schwanomas are usually free of neurogenic effect. Paragangliomas are spindle shaped well capsulated ,brownish tumor that may arise from vagus, hypoglossal and carotid body and occupies the space [Figure 3]. Occasionally they may extend up through skull base, and have intracranial extension [Figure 4] [2]. Aneurysm from carotid vessel is also possible. Metastatic tumor [Figure 5] and lymphomas are other possible malignant lesions of the region.

 HISTOLOGY



Paragangliomas may contain cluster cells of epithelial cells of Zellballen in highly vascular stroma. They may secrete catecholamine. In schwanoma, nerve coverings undergo neoplastic transformation. Antoni type A arrangements of nuclei and Verucay bodies are found here. In case of infection of this region, polymicrobial infection, usually the oropharyngeal flora is commonly found. Only in cases of immunocompromised patients, unusual organisms are discovered [4]

 CLINICAL PRESENTATION



Patients with parapharyngeal space infection present with fever, trismus, perimandibular edema. Tumors of the region are mostly slow growing, presenting with cervical swelling and muffled voice. Parotid swellings were present in cases of parotid pathology. Tonsil bulge is commonly found on patient examination.

 TREATMENT



Treatment is mostly surgical. In cases of malignancy, after resection of primary tumor, combined therapy is used to treat residual disease. Parapharyngeal space infection is treated conservatively and abscess drained by external submandibular approach. Retropharyngeal abscess may be drained in Rose position transorally, or, if respiratory obstruction or significant inferior extension present, then by anterior cervical approach as described by Dean, is preferred [5].

 RADIOGRAPHIC FEATURES



Parapharyngeal pathologies are less identified by conventional radiology. Though before advent of CT Scanning and MR images, conventional radiography and angiography were primary tools in diagnosis.

 RETROPHARYNGEAL ABSCESS



Collection in retropharyngeal space could easily be identified by conventional radiography and forms basis before drainage. Wholey and colleagues have demonstrated Retropharyngeal space exceeding 7mm in both adults and children or increase in retrotracheal space to more than 22mm in adults and 14 mm in children [6] as also loss of cervical lordosis is virtually diagnostic for retropharyngeal abscess [Figure 6]. Occasionally a horizontal fluid level is identified, suggesting of presence of pus and gas in the enclosed space. Source of gas may be due to esophageal rupture due to iatrogenic trauma or foreign body, but also may be due to gas forming organism, or both. When pus that has accumulated between buccopharyngeal fascia and alar fascia ruptures into prevertebral space (named dangerous space by Grodinsky), it may easily pass down onto posterior mediastinum causing mediastinitis. CT Scan is equally efficient to identify these lesions [Figure 7]. Fortunately with development of antibiotics these infection have come down.

 PARAPHARYNGEAL SPACE INFECTION



Abscess of parapharyngeal space may result from lateral spread of an advanced tonsillar infection or from medial extension of an odontogenic infection arising in masticator space. Though conventional radiography may not identify the involvement, CT with contrast may evaluate the extent of pathology [Figure 8]. Carotid space forms main conduit for spread of infection to and from mediastinum, and has been named " Mosher-- Lincoln Highway of the neck [7]."

 MASSES OF PARAPHARYNGEAL SPACE & CT EVALUATION:-



PRESTYLOID COMPARTMENT

Localizing a mass to the parapharnygeal space may be difficult. Primary parapharyngeal prestyloid mass usually displace deep lobe of parotid gland laterally, and does not extend into deep lobe of parotid gland. These masses are unifocal where as parotid masses may be multifocal [8]. These masses may also be difficult to separate from deep extension of primary masticator space lesion. They are seperated from their relation to medial pterygoid muscle, with parapharyngeal mass lying medial to it. Primary prestyloid parapharyngeal masses may be - Minor salivary gland tumor, atypical type II first branchial cleft anomaly and lipoma. Secondary masses may be, deep spread of malignant tumor from adjacent spaces [Figure 9], squamous cell carcinoma from visceral spaces. Sarcoma from masticator and extension of tumor from parotid space. Most common lesions results from secondary extension of pathologic process arising from adjacent spaces. Of these most common is deep extension of squamous cell carcinoma arising in tonsillar region [Figure 10]. Spread into parapharyngeal space is important to surgeons as it contraindicates resection of tonsillar carcinoma with wide local extension, through an intraoral approach.

 CAROTID SPACE



It is poststyloid compartment of parapharyngeal space. It contains internal carotid artery, internal jugular vein, sympathetic chain, cranial nerves IX to XII and lymph nodes. It extends from jugular foramen to aortic arch Lesions that could be expected in this region are as follows--

CAROTID ARTERY -- Ectasia, Aneurysm, Dissection, Encasement by direct squamous cell carcinoma.

JUGULAR VEIN- Asymmetric enlargement, Thrombosis, Thrombophlebitis, Meningioma (from jugular foramen)

CRANIAL NERVES AND SYMPATHETIC CHAIN -- Neurogenic Tumor, Neuroblastoma, Paraganglioma

LYMPH NODE-- Metastatic cervical adenopathy, Lymphoma.

Majority of masses that involve the carotid sheath are lesions that originate primarily within this space. Masses involving carotid artery or jugular vein are easily identified by contrast enhanced CT scan. Paragangliomas and neurogenic tumors may arise in similar location. Presence of internal tumors may arise in similar location. Presence of internal flow voids on MR Imaging in a mass that is greater than 2 cm is suggestive of paraganglioma, rather than Schwanoma. Flow voids are not helpful in distinguishing between these two lesions when their mean diameter is less than 2 cm. Enlarged lymph nodes are most common pathology of carotid sheath. Enlarged nodes with areas of decreased central attenuation may be either due to neoplastic or inflammatory cause. Enlarged lymph node that appear very vascular or cystic are suggestive of metastasis from thyroid carcinoma [Figure 11].

For suspected carotid body and vagal paraganglioma, thin section CT scanning [Figure 2][Figure 3] is performed, with the use of contrast material from skull base to thoracic inlet at 2.5 - 3 mm intervals in the axial plane. Coronal scan may be obtained indirectly with reformation of axial data. Bone or soft tissue algorithms may be reconstructed from the original data. CT Scanning is useful to demonstrate the integrity of associated soft tissue and the detection of multiple lesions [9]. Splaying of Internal and External carotids and Lyre's sign suggests the diagnosis of carotid body tumor. [10]

 MAGNETIC RESONANCE IMAGING



The role of MR Imagining [Figure 12] in the diagnosis and preoperative assessment of paragangliomas has been established. [11],[12] MRI allows evaluation of these lesions and adjacent soft tissue and vascular structure without use of ionizing radiation. Imaging characteristics of all paragangliomas are similar. A well-defined hypointense mass with areas of signal void is seen on T1 weighed images. Long TR/TE images also demonstrate a well-defined mass, which is heterogeneously hyperintense. Punctate flow voids are seen and are believed to represent hypervascular nature of the tumor. Oslen et al described chronic appearance of paraganglioma, that is, a salt pepper appearance in all lesions larger than 2 cm in diameter [13]. Pattern more commonly is seen in T2WI, and the dark and bright appearances in the lesion represents the high vascularity in the mass with associated areas of haemorrhage, slow flowing blood and tumor cells. A drop out sign has been described by Vogl et al [14] for skull base paragangliomas. This effect was seen after a large bolus of IV Contrast was infused, where by susceptibility effects from the contrast led to an abrupt drop off in signal intensity on gradient echo MRI 24 - 42 seconds after the bolus, independent of location, size, or classification of glomus tumor. With time susceptibility effect diminishes and increased signal intensity could be seen.

 ULTRASOUND AND CAROTID BODY TUMOR



This modality is useful in the evaluation and follow up of carotid body tumors. Vagal paraganglioma if palpated in lower neck could be imaged with ultrasound. Gray scale ultrasound is used for delineation of tumor margins [Figure 13], size and location. Color Doppler flow imaging is useful to show hypervascular nature [Figure 14]. USG may also differentiate Carotid body tumor from vascular anomalies and pseudoaneurysm [15]. USG can differentiate vagal paragangliomas from other lesions of neck, such as lymph nodes, metastasis and vascular abnormality.

 RADIONUCLIDE TECHNIQUE



Radiolabelled compounds that bind to receptors in tumors form the basis of receptor imaging [Figure 15]. Pentetreotide is an octreotide that, when used for imaging gives information about number and distribution of paragangliomas.

 ANGIOGRAPHY



Non-invasive imaging CT Angiogram and MR Angiogram [Figure 16] have almost completely replaced angiography as primary radiographic tool in the diagnosis of paraganglioma. [16,17] Accurate assessment and safe embolisation of these lesions require an extensive knowledge of normal vascular anatomy, collateral circulation, congenital variations and vascular physiology.

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