malignant parotid tumours

8/12/2019 Malignant Parotid Tumours

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Introduction and Anatomy

The parotid glands are the largest salivary glands in humans and are frequentlyinvolved in disease processes. Approximately 25% of parotid masses arenonneoplastic; the remaining 75% are neoplastic.

Nonneoplastic causes of parotid enlargement include cysts,parotitis,lymphoepithelial lesions associated with AIDS, collagen vascular diseases, andbenign hypertrophy. Benign hypertrophy is encountered in patientswithbulimia,sarcoidosis,sialosis,actinomycosis infections,andmycobacterialinfections.The vast majority (approximately 80%) of parotid neoplasms arebenign; these are discussed in detail in the Medscape Reference articleBenignParotid Tumors.

The paired parotid glands are formed as epithelial invaginations into theembryological mesoderm and first appear at approximately 6 weeks gestation.The glands are roughly pyramidal in shape, with the main body overlying the

masseter muscle.

The glands extend to the zygomatic process and mastoid tip of the temporalbone and curve around the angle of the mandible to extend to theretromandibular and parapharyngeal spaces. The parotid duct exits the glandmedially, crosses the superficial border of the masseter, pierces the buccinator,and enters the oral cavity through the buccal mucosa opposite the secondmaxillary molar.

The gland is divided into a superficial and deep portion by the facial nerve, whichpasses through the gland. While not truly anatomically discrete, these "lobes" areimportant surgically, as neoplasms involving the deep lobe require sometimessignificant manipulation of the facial nerve to allow excision. The superficial lobeis the larger of the two and thereby the location of the majority of parotid tumors.

The facial nerve exits the cranium via the stylomastoid foramen and coursesthrough the substance of the parotid gland. The superficial lobe of the parotid liessuperficial or lateral to the facial nerve, whereas the deep lobe is deep or medialto the facial nerve. The facial nerve branches within the substance of the parotidgland, and the branching pattern can be highly variable. The main trunk typicallybifurcates in to the zygomaticotemporal branch and the cervicofacial branch atthe pes anserinus, also known as the gooses foot (see images below), andthereafter into the temporal, zygomatic, buccal, marginal, and cervical branches.

Pes is about 1.3 cm from the stylomastoid foramen. Extensive anastomoses areusually present between branches of the zygomatic and buccal branches of thenerve.
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The (Z) zygomaticotemporal branch and the (C)cervicofacial branch of the facial nerve are dissected out during resection of a parotid tumor.

The pes (goose's foot) is visible in this photograph. Thesurgical anatomy and landmarks of the facial nerve.Numerous lymph nodes also are present within the parotid gland itself,subsequently draining to preauricular, infra-auricular, and deep upper jugularnodes.

Diagnosis

Evaluation of a patient with a suspected parotid gland malignancy must beginwith a thorough medical history and physical examination.

The most common presentation is a painless, asymptomatic mass; >80% ofpatients present because of a mass in the posterior cheek region. Approximately30% of patients describe pain associated with the mass, though most parotidmalignancies are painless. Pain most likely indicates perineural invasion, whichgreatly increases the likelihood of malignancy in a patient with a parotid mass.

Of patients with malignant parotid tumors, 7-20% present with facial nerveweakness or paralysis, which almost never accompanies benign lesions andindicates a poor prognosis. Approximately 80% of patients with facial nerveparalysis have nodal metastasis at the time of diagnosis. These patients have an

average survival of 2.7 years and a 10-year survival of 14-26%.

Other important aspects of the history include length of time the mass has beenpresent and history of prior cutaneous lesion or parotid lesion excision. Slow-growing masses of long-standing duration tend to be benign. A history ofpriorsquamous cell carcinoma,malignant melanoma,ormalignant fibroushistiocytomasuggests intraglandular metastasis or metastasis to parotid lymph
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nodes. Prior parotid tumor most likely indicates a recurrence because ofinadequate initial resection.

Trismus often indicates advanced disease with extension into the masticatorymuscles or, less commonly, invasion of the temporomandibular

joint.Dysphagiaor a sensation of a foreign body in the oropharynx indicates atumor of the deep lobe of the gland. A report of ear pain may indicate extensionof the tumor into the auditory canal. The presence of numbness in the distributionof the second or third divisions of the trigeminal nerve often indicates neuralinvasion.

Physical examination of the head and neck must be thorough and complete. Theentire head and neck must be examined for cutaneous lesions, which mayrepresent malignancies that could metastasize to the parotid gland or parotidnodes.

Palpation of the mass should determine the degree of firmness. Even benign

tumors are usually firm, but a rock-hard mass generally denotes malignancy. Skin fixation, skin ulceration, or fixation to adjacent structures also indicates

malignancy. The external auditory canal must be visualized for tumor extension. All regional nodes must be carefully palpated to detect nodal metastasis.

Examination of the oral cavity and oropharynx also may yield further evidenceof metastasis or malignant nature of the lesion.

Blood or pus from the Stenson duct is a sign of malignancy but is infrequentlyencountered. More often, one may see bulging of the lateral pharyngeal wall orsoft palate, indicating tumor in the deep lobe of the gland.

Bimanual palpation with one finger against the lateral pharyngeal wall and theother against the external neck may confirm extent into the tonsillar fossa and

soft palate.Once a thorough history and physical examination are complete, performdiagnostic procedures to confirm the diagnosis and extent of the disease process.

Fine needle aspiration

Fine needle aspiration of the mass or an enlarged lymph node may be performedto obtain a tissue diagnosis.[1] Most surgeons recommend excision of a parotidmass whether it is benign or malignant unless a patient's comorbidity precludessafe surgery. As such, many surgeons do not routinely perform cytology beforeproceeding with surgery.

The sensitivity of this procedure is greater than 95% in experienced hands.However, only a positive diagnosis should be accepted; negative results indicatethe need for further attempts at obtaining a histologic diagnosis, including repeatfine needle aspiration.

The results of the fine needle aspiration provide a histologic diagnosis and assistin preoperative planning and patient counseling. It may not distinguish benignfrom malignant epithelial lesions because malignancy of parotid epithelial cells isrelated to the behavior of the tumor cells in relation to tissue planes andsurrounding structures rather than cellular architecture, which may be rather
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normal even in malignancy. Therefore, nonepithelial lesions may be diagnosedwith accuracy, but epithelial lesions may require further investigation.

If fine needle aspiration is unsuccessful in obtaining a diagnosis, an incisionalbiopsy should not be performed. This procedure has a high rate of localrecurrence and places the facial nerve at risk for injury from inadequate

visualization. Some authors advocate large core needle biopsies, but this procedure is less

popular because of potential facial nerve injury and the possibility of seeding theneedle tract with tumor cells.

If a core biopsy is performed, the needle should be inserted so that the tract maybe excised during the definitive operation. When all attempts at obtaining ahistologic diagnosis have failed, operative exploration should proceed afterappropriate imaging studies have been obtained.

Intraoperatively, a frozen section of the specimen should be submitted fordiagnosis. The use of frozen sections has demonstrated greater than 93%accuracy in the diagnosis of parotid malignancy.

Imaging studies Imaging studies may be helpful in staging and for surgical planning. Sialography may help differentiate inflammatory versus neoplastic processes, but

this test is infrequently performed and is of limited value in the evaluation ofparotid masses. It is mentioned herein for historic interest only.

Sonography may be very useful. Benign lesions are of lower density and havesmaller caliber blood vessels. However, determination of a cystic componentmay be misleading, because cystic degeneration may occur as a result ofnecrosis at the avascular center of a malignancy.

CT scan and MRI[2] can be valuable for evaluation of parotid malignancies. CTscanning provides better detail of the surrounding tissues, whereas MRI

demonstrates the mass in greater contrast than a CT scan. These imaging studies may identify regional lymph node involvement or

extension of the tumor into the deep lobe or parapharyngeal space. CT scancriteria for lymph node metastasis include any lymph node larger than 1-1.5 cmin greatest diameter, multiple enlarged nodes, and nodes displaying centralnecrosis.

Lymph nodes harboring metastasis also may appear round rather than thenormal kidney bean shape, and evidence of extracapsular extension may beidentified.

For more information on imaging studies for malignant parotid tumors, seeMedscape Reference Radiology articleMalignant Parotid Tumor Imaging.

PathologyMany types of parotid malignancies exist, most arising from the epithelialelements of the gland.[3, 4, 5, 6, 7] Classification of these tumors can be quiteconfusing. In addition, malignancy may develop in the secretory element of thegland or malignancy arising elsewhere may first be noticed as a metastasis to thegland.
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Acinic cell carcinoma

Acinic cell carcinoma is an intermediate-grade malignancy with low malignantpotential. This tumor may be bilateral or multicentric and is usually solid, rarelycystic.

Although this tumor rarely metastasizes, occasional late distant metastases havebeen observed. This tumor also may spread along perineural planes. Overall 5-year survival is 82%, and 10-year survival is 68%.

Adenocarcinoma

Adenocarcinoma of the parotid develops from the secretory element of the gland.This is an aggressive lesion with potential for both local lymphatic and distantmetastases.

Approximately 33% of patients have nodal or distant metastasis present at thetime of initial diagnosis. Overall 5-year survival is 19-75%, as it is highly variableand related to grade and stage at presentation.Primary squamous cell carcinoma

Primary squamous cell carcinoma of the parotid is rare, and metastasis fromother sites must be excluded.

Overall 5-year survival is 21-55%, and 10-year survival is 10-15%.

Sebaceous carcinoma

Sebaceous carcinomais a rare parotid malignancy that often presents as apainful mass.

It commonly involves the overlying skin.

Salivary duct carcinoma

Salivary duct carcinoma is a rare and highly aggressive tumor.

Small cell carcinoma exists as 2 types. The ductal cell origin type is mostlybenign and rarely metastasizes. The neuroendocrine origin type is oftenaggressive and has higher metastatic potential.

Lymphoma

The parotid gland also may be the site of occurrence of lymphoma, mostcommonly in elderly males. This is also observed in approximately 5-10% ofpatients with Warthin tumor of the parotid gland, a benign neoplasm.[12]

The entire parotid is typically enlarged with a rubbery consistency on palpation.Often, regional nodes also are enlarged. Biopsy of enlarged regional nodesavoids unnecessary parotid surgery, as the definitive treatment consists ofchemotherapy or radiation therapy.

Malignant fibrohistiocytoma

Malignant fibrohistiocytoma is very rare in the parotid gland. It presents as a slowgrowing and painless mass.

Fine needle aspiration and imaging could confuse them with other kinds ofparotid tumors; therefore, definite diagnosis should be based onimmunohistochemical analysis of the resected tumor.

The tumor should be completely resected.[13]
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Parotid metastasis from other sites

The parotid also may be the site of metastasis from cutaneous, renal, lung,breast, prostate, or GI tract malignancies.

Operative Management

Generally, therapy for parotid malignancy is complete surgical resection followed,when indicated, by radiation therapy.[14] Conservative excisions are plagued by ahigh rate of local recurrence. The extent of resection is based on tumor histology,tumor size and location, invasion of local structures, and the status of regionalnodal basins.

Most tumors of the parotid (approximately 90%) originate in the superficial lobe.Superficial parotid lobectomy is the minimum operation performed in thissituation. This procedure is appropriate for malignancies confined to thesuperficial lobe, those that are low grade, those less than 4 cm in greatestdiameter, tumors without local invasion, and those without evidence of regional

node involvement.

Surgical resection procedure

The most important initial step is identification of the facial nerve and its coursethrough the substance of the parotid gland. In order to preserve the facial nerve,it is important to try to determine the proximity of the nerve to the capsule of thetumor prior to surgery. Results of a retrospective review showed that malignanttumors were likely to have a positive facial nerve margin.[15] Virtually all surgeonsavoid using paralytic agents, and, to assist finding the nerve, many surgeons usea nerve stimulator. Increasingly, surgeons are using intraoperative continuousfacial nerve monitoring any time a parotidectomy is performed. This is not usually

necessary in the primary setting, but recurrent resections may be very difficultand probably should be performed using this device.

Ideally, the dissection of the facial nerve should be performed withoutdisturbing or violating the tumor. The facial nerve may be found exiting thestylomastoid foramen by reflecting the parotid gland anteriorly and thesternocleidomastoid muscle posteriorly. Landmarks include the digastric ridgeand the tympanomastoid suture. Knowledge of the relationships among thesestructures allows more efficient and reproducible identification of the nerve.

The cartilaginous external auditory canal lies approximately 5 mm superior tothe facial nerve in this region. The facial nerve is also anterior to the posterior

belly of the digastric muscle and external to the styloid process. A second technique for locating the facial nerve is to identify a distal branch of

the nerve and to dissect retrograde toward the main trunk. This technique maybe more difficult depending on the ease of identifying the branching pattern. Toperform this maneuver, the buccal branch may be found just superior to theparotid duct, or the marginal mandibular branch may be found crossing over(superficial to) the facial vessels. These may then be traced back to the originsof the main facial nerve trunks.


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A final way of identifying the nerve in particularly difficult situations is to drill themastoid and to locate the nerve within the temporal bone. It may then befollowed through the stylomastoid foramen antegrade towards the parotid.

Once these have been identified, the superficial lobe of the parotid gland maybe removed en bloc and sent to the pathology laboratory.

If the immediate intraoperative pathologic examination reveals that the tumor isactually high-grade or >4 cm in greatest diameter, or lymph node metastasis isidentified within the specimen, a complete total parotidectomy should beperformed.

If the facial nerve or its branches are adherent to or directly involved by thetumor, they must be sacrificed. However, a pathologic diagnosis of malignancymust be confirmed intraoperatively prior to sacrificing facial nerve branches.

All involved local structures should be resected in continuity with the tumor.This may include skin, masseter, mandible, temporalis, zygomatic arch, ortemporal bone.

Tumors of the deep lobe are treated by total parotidectomy. Identification of the

facial nerves and branches is the first and most crucial step. Total parotidectomy is then performed en bloc, and the fate of the facial nerve

and surrounding local structures must be decided similar to superficial lobetumors. The specimen should be sent to the pathology laboratory for immediateexamination.

Neck dissection should be performed when malignancy is detected in thelymph nodes pre- or intraoperatively.

Other indications for functional neck dissection include tumors >4 cm ingreatest diameter, tumors that are high-grade, tumors that have invaded localstructures, recurrent tumors when no neck dissection was performed initially,and deep lobe tumors.

These recommendations are based on the higher likelihood of occult, clinicallyundetectable nodal disease present at the time of operation in patients whosetumors display the above characteristics.

Reconstruction

Following resection of the tumor specimen, most wounds can be closed primarily.However, the presence of extension of the tumor to the overlying skin orsurrounding structures may require reconstructive procedures. The overall goalfollowing tumor excision is to restore function and achieve the best possibleaesthetic result.

Options for wound closure in the presence of a skin or soft tissue deficit include

skin grafting, cervicofacial flap, trapezius flap, pectoralis flap, deltopectoral flap,and microvascular free flap. For information on various flap procedures, seetheFlapssection of the Medscape ReferencePlastic Surgeryjournal.

Sacrifice of the facial nerve or one of its branches also must be managedappropriately. If inadvertently severed during the operation, the facial nerveshould be immediately repaired under the operating microscope. If intentionally
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resected with the tumor specimen, several options for reconstruction areavailable to the surgeon.

The ipsilateral or contralateral great auricular nerve may be used as aninterposition graft, although this sacrifices sensation to the area normallysupplied by this nerve.

Another option is to anastomose the facial nerve to the ipsilateral hypoglossalnerve. This anastomosis may be performed end-to-side to avoid interfering withnormal hypoglossal nerve function.

During the period of waiting for facial nerve recovery, maintain cornealprotection if the innervation to the orbicularis oculi has been interrupted.

Measures include taping the eye closed at night over ophthalmic ointment andfrequent use of wetting drops during the day. Some authors recommend amoisture chamber.

If facial nerve recovery is not achieved, certain measures may be taken toimprove form and function.

A gold weight (0.8-1.2 g) may be inserted in the upper eyelid to assist withclosure. Dynamic slings of temporalis muscle to the upper and lower lids andcorner of the mouth or masseter sling to the mouth have proven verysuccessful in the reconstruction of these patients. Static slings also have beenused and include fascia lata, tendon, and Mitek anchors.

Following parotidectomy, some patients develop gustatory sweating or Freysyndrome.[16] This denotes an aberrant connection of regeneratingparasympathetic salivary fibers to the sweat glands in the overlying skin flap.Treatment of this condition has included irradiation, atropinelike creams,division of the auriculotemporal nerve (sensory), division of theglossopharyngeal nerve (parasympathetic), insertion of synthetic materials

(AlloDerm), fascial grafts, or vascularized tissue flaps between the parotid bedand overlying skin flap. Intracutaneous injections ofbotulinum toxin Ais also anattractive option which has showed some promise.

Finally, neurovascular free tissue transfer has been described for facialreanimation for treatment of established facial paralysis following ablative parotidsurgery.[17]

Vascularized nerve grafts, such as sural nerve graft, have been described toreestablish facial nerve continuity.

Functional free muscle transfer with gracilis, pectoralis minor, or latissimusdorsi muscles are further options for reconstruction. The ipsilateral facial nerve

stump may be used as the recipient nerve. Alternatively, cross facial nerve grafting can be performed. This is typically

performed as a 2-stage surgery, with anastomosis to a nerve graft as the firststage and free tissue transfer as the second stage.

For more information on facial nerve reconstruction and the treatment of facialnerve paralysis, see Medscape Reference articlesFacial NerveParalysis,Dynamic Reconstruction for Facial Nerve Paralysis,andStaticReconstruction for Facial Nerve Paralysis.
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Adjunctive Therapy

Because of the many histologic subtypes of parotid malignancies, a generalstatement regarding the usefulness of adjunctive therapy cannot be made.

If resectable, surgery is the primary modality of treatment for most malignant

tumors of the parotid gland. General indications for postsurgical radiation therapyinclude tumors >4 cm in greatest diameter, tumors of high grade, tumor invasionof local structures, lymphatic invasion, neural invasion, vascular invasion, tumorpresent very close to a nerve that was spared, tumors originating in or extendingto the deep lobe, recurrent tumors following re-resection, positive margins onfinal pathology, and regional lymph node involvement. Postoperative radiation is,thus, usually indicated for all parotid malignancies with the exception of smalllow-grade tumors with no evidence of local invasion or nodal/distant spread.Radiation therapy is considered the cornerstone of adjunctive therapy.

No chemotherapy has been proven effective as single modality therapy. For

certain histologic subtypes, some clinicians recommend combined modalitychemotherapy and radiation. Presently, immunotherapy is in the clinical trialphase.

A recent study demonstrated that epidermal growth factor receptor (EGFR) isexpressed strongly in the cell membranes of parotid mucoepidermoid carcinomasand of the lymph node metastases.[18] EGFR-targeting agents have potential to beused for therapy.

Prognosis

The major determinants of survival are histology and clinical stage. Poor

prognostic factors include high grade, neural involvement, locally advanceddisease, advanced age, associated pain, regional lymph node metastases,distant metastasis, and accumulation of p53 or c-erbB2 oncoproteins.[19, 20, 21, 22]

Although statements regarding survival are difficult to make because of the largevariety of histologic types, 20% of all patients will develop distantmetastases.[23]The presence of distant metastases heralds a poor prognosis, witha median survival of 4.3-7.3 months.

Overall 5-year survival for all stages and histologic types is approximately 62%.The overall 5-year survival for recurrent disease is approximately 37%. Because

of the risk of recurrence, all patients who have had a histologically provenmalignant salivary gland tumor should have lifelong follow-up.

Surveillance

Surveillance must continue indefinitely, as local recurrence or distant metastasesmay become apparent many years after the initial treatment.


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malignant parotid tumours

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