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Parotid gland

The document discusses the anatomy, development, disorders, and tumors of the parotid gland. It begins by describing the location and structures of the parotid gland. It then discusses various inflammatory and infectious disorders that can affect the gland such as mumps, bacterial infections, and HIV-associated sialadenitis. Obstructive disorders from stones, strictures, or papillary obstruction are also reviewed. The majority of the document focuses on tumors of the parotid gland, describing the classification and most common tumor types as well as their presentation, investigations, and surgical management.

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MOSTAFA HEGAZY
THE PAROTID GLAND Anatomy  The parotid gland lies in a recess bounded by the ramus of the mandible, the base of the skull and the mastoid process.  It lies on the carotid sheath and CNs XI and XII and extends forward over the masseter muscle.  The gland is enclosed in a sheath of dense deep cervical fascia.  Its upper pole extends just below the zygoma and its lower pole (tail) into the neck.
THE PAROTID GLAND Anatomy Several important structures run through the parotid gland. These include: ● Facial nerve trunk that divides into its major five branches; ● Terminal branch of the external carotid artery that divides into the maxillary artery and the superficial temporal artery; ● Retromandibular vein; ● Intraparotid lymph nodes.
THE PAROTID GLAND Anatomy  The gland is arbitrarily divided into deep and superficial lobes, separated by the facial nerve.  Eighty per cent of the parotid gland lies superficial and 20% deep to the nerve.  An accessory lobe is occasionally present lying anterior to the superficial lobe on the masseter muscle.
Developmental disorders  Developmental disorders such as agenesis, duct atresia and congenital fistula are extremely rare
Inflammatory disorders Viral infections  Mumps is the most common cause of acute painful parotid swelling and predominantly affects children.  It is spread via airborne droplets of infected saliva.  The disease starts with a prodromal period of 1–2 days, during which the patient experiences fever, nausea and headache.  This is followed by pain and swelling in one or both parotid glands.
Inflammatory disorders Viral infections  Parotid pain can be very severe and exacerbated by eating and drinking.  Symptoms resolve within 5–10 days.  The diagnosis is based on history and clinical examination; recent contact with an infected patient with a painful parotid swelling is often sufficient to lead to a diagnosis.
Inflammatory disorders Viral infections  Atypical viral parotitis does occur and may present with predominantly unilateral swelling or even submandibular involvement.  A single episode of infection confers lifelong immunity.
Inflammatory disorders Viral infections  Treatment of mumps is symptomatic with regular paracetamol and adequate oral fluid intake.  Complications of orchitis, oophoritis, pancreatitis, sensorineural deafness and meningoencephalitis are rare, but are more likely to occur in adults.  Other viral agents that produce parotitis include Coxsackie A and B, parainfluenza 1 and 3, Echo and lymphocytic choriomeningitis.
Inflammatory disorders Bacterial infections  Acute ascending bacterial sialadenitis is historically described in dehydrated elderly patients following major surgery.  Reduced salivary flow secondary to dehydration results in ascending infection via the parotid duct into the parotid parenchyma.  The more common picture today is an acute bacterial parotitis associated with a salivary calculus.
Inflammatory disorders Bacterial infections  The patient presents with a tender, painful parotid swelling that arises over several hours .  There is generalized malaise, pyrexia and occasional cervical lymphadenopathy.  The pain is exacerbated by eating or drinking.  The parotid swelling may be diffuse, but often localizes to the lower pole of the gland.  Intraoral examination may reveal pus exuding from the parotid gland papilla
Inflammatory disorders Bacterial infections  The infecting organism is usually Staphylococcus aureus or Streptococcus viridans, and treatment is with appropriate intravenous antibiotics.  If the gland becomes fluctuant, ultrasound may identify abscess formation within the gland that may require aspiration with a large-bore needle or formal drainage under general anesthesia.
Inflammatory disorders Bacterial infections  In the latter procedure, the skin incision should be made low to avoid damage to the lower branch of the facial nerve.  Blunt dissection using sinus forceps is preferred, and the cavity is opened to facilitate drainage.
Inflammatory disorders Bacterial infections  A drain is inserted and left in situ for 24–72 hours.  Sialography is contraindicated during acute infection.  Chronic bacterial sialadenitis is rare in the parotid gland.
Recurrent parotitis of childhood  Recurrent parotitis of childhood is a distinct clinical entity of unknown etiology and variable prognosis.  It is characterized by rapid swelling of one or both parotid glands, in which the symptoms are made worse by chewing and eating.  Systemic upset with fever and malaise is variable.
Recurrent parotitis of childhood  The symptoms usually last from 3 to 7 days, and are then followed by a quiescent period of weeks to several months.  Children usually present between the ages of 3 and 6 years, although symptoms have been reported in infants as young as 4 months.
Recurrent parotitis of childhood  The diagnosis is based on the characteristic history and can be confirmed by Sialography.  This shows a characteristic punctate sialectasis likened to a ‘snowstorm’ .  The condition is difficult to manage if it becomes established and so the initial treatment is important.
Characteristic ‘snowstorm’ appearance of recurrent parotitis of childhood (circled)
Recurrent parotitis of childhood  The condition responds to regular endoscopic washouts and long courses of antibiotics.  The suspicion is that in some cases the condition is caused by an incompetent punctum that leads to soiling of the parotid ducts with contaminated oral fluids.
Human immunodeficiency virus-associated sialadenitis  Chronic parotitis in children may signify human immunodeficiency virus (HIV) infection.  The presentation of HIV-associated sialadenitis is very similar to classical Sjögren’s syndrome in adulthood  Although HIV-associated sialadenitis and Sjögren’s syndrome are histologically similar, the former condition is usually associated with a negative autoantibody screen.
Human immunodeficiency virus-associated sialadenitis  Other presentations of salivary gland disease in HIV- positive patients include multiple parotid cysts, which  cause gross parotid swelling and facial disfigurement.  CT and MRI demonstrate the characteristic ‘Swiss cheese’ appearance of multiple large cystic lesions.  The swollen glands are usually painless and may regress on the institution of antiviral therapy.  Cysts can be aspirated
Obstructive parotitis  There are several causes of obstructive parotitis, which produces intermittent painful swelling of the parotid gland, particularly at mealtimes;  Stone formation and strictures  Papillary obstruction
Obstructive parotitis Stone formation and strictures  Sialolithiasis is less common in the parotid gland (20%) than in the submandibular gland (80%).  Parotid duct stones are usually radiolucent and rarely visible on plain radiography.  They are frequently located at the confluence of the collecting ducts, at the point the duct courses over the masseter muscle or in the distal aspect of the parotid duct adjacent to the parotid papilla.
Obstructive parotitis Stone formation and strictures  The stones are easily demonstrated on ultrasound.  The same rules for treatment apply to parotid stones as to submandibular duct stones. Small stones (~4 mm) can be retrieved by baskets, slightly larger stones up to 8 mm can be broken with lithotripsy and stones over 8 mm diameter should be removed by endoscopic assisted surgery while preserving the gland.
Obstructive parotitis Stone formation and strictures  The stones are easily demonstrated on ultrasound.  The same rules for treatment apply to parotid stones as to submandibular duct stones. Small stones (~4 mm) can be retrieved by baskets, slightly larger stones up to 8 mm can be broken with lithotripsy and stones over 8 mm diameter should be removed by endoscopic assisted surgery while preserving the gland.
Obstructive parotitis Stone formation and strictures  Strictures are common in the parotid gland and are  responsible for about 20% of obstructive cases.  The symptom complex is a little different as the obstruction is due to mucus plugs.  These form after periods of stagnation.  Classically, the patient complains of a meal-time syndrome starting at breakfast and the saliva cannot seep past the mucus plug so the swelling persists.
Obstructive parotitis Stone formation and strictures  Massage eventually releases the plug with a gush of salty saliva.  Infection is uncommon unless there is stone formation.  Strictures respond to dilatation and endoscopic washouts with steroid solutions.
Papillary obstruction  Obstructive parotitis, can be caused by trauma to the parotid papilla.  The subsequent inflammation and edema obstructs salivary flow, particularly at mealtimes.  This is a rare but real entity.
Papillary obstruction  The partial obstruction over a protracted period leads to dilation of the duct and an entity called ‘mega-duct’.  A large dilated duct is visible coursing over the patient’s cheek.  Drainage has to be re-established.
Papillary obstruction  This can be done by progressive dilatation of the punctum and the insertion of a stent that is kept in position for many weeks.  Surgical attempts to refashion the punctum are unlikely to be successful.
Papillary obstruction  Papillotomy should not be performed as this often leads to stricture formation and a life time of problems.  This is not the case with the submandibular gland.
Tumors of the parotid gland The parotid gland is the most common site for salivary tumors. Most tumors arise in the superficial lobe and present as slow-growing, painless swellings below the ear in front of the ear or in the upper aspect of the neck.
Tumors of the parotid gland Less commonly, tumors may arise from the accessory lobe and present as persistent swellings within the cheek. Rarely , tumors may arise from the deep lobe of the gland and present as a parapharyngeal mass.
Benign tumour of the left parotid gland producing characteristic deflection of the ear lobe.
Pleomorphic adenoma arising from the upper pole of the left parotid gland producing a preauricular swelling
Deep lobe tumour of the right parotid presenting with a swelling of the right soft palate.
Magnetic resonance imaging scan revealing a large deep lobe tumour (arrow) of the right parotid gland, occupying the parapharyngeal space.
Tumors of the parotid gland  Symptoms include difficulty in swallowing and snoring.  Clinical examination reveals a diffuse firm swelling in the soft palate and tonsil.  Some 80–90% of tumours of the parotid gland are benign, the most common being pleomorphic adenoma.
Tumors of the parotid gland Malignant salivary gland tumors are divided into two distinct sub-groups:
Tumors of the parotid gland 1 Low-grade malignant tumors (e.g. acinic cell carcinoma) are indistinguishable on clinical examination from benign neoplasms.
Tumors of the parotid gland 2 High-grade malignant tumors usually present as rapidly growing, often painless swellings in and around the parotid gland.
Tumors of the parotid gland The tumour presents as either a discrete mass with infiltration into the overlying skin or  a diffuse but hard swelling of the gland with no discrete mass.
Tumors of the parotid gland Presentation with advanced disease is common, and cervical lymph node metastases may be present.
Tumors of the parotid gland Among primary parotid malignant tumors, mucoepidermoid carcinoma is the most common, followed by adenocystic carcinoma. The latter is notorious for its proclivity for perineural invasion and metastatic potential so surgery is normally supported by adjuvant radiotherapy to gain local control of the disease.
Classification of salivary gland tumours (simplified). I Adenoma  Pleomorphic : Pleomorphic adenoma  Monomorphic : Adenolymphoma (Warthin’s tumour)
Classification of salivary gland tumours (simplified). II Carcinoma Low grade  Acinic cell carcinoma  Adenoid cystic carcinoma  Low-grade mucoepidermoid carcinoma High grade  Adenocarcinoma  Squamous cell carcinoma  High-grade mucoepidermoid carcinoma
Classification of salivary gland tumours (simplified). III Non-epithelial tumors  Haemangioma, lymphangioma IV Lymphomas Primary lymphomas  Secondary lymphomas  Non-Hodgkin’s lymphomas  Lymphomas in Sjögren’s syndrome V Secondary tumors  Local : Tumors of the head and neck especially  Distant: Skin and bronchus
Classification of salivary gland tumours (simplified). VI Unclassified tumors VII Tumour-like lesions Solid lesions  Benign lymphoepithelial lesion  Adenomatoid hyperplasia Cystic lesions  Salivary gland cysts
Malignant tumour of the left parotid gland with invasion of the overlying skin.
Investigations  The initial imaging modality of choice is ultrasound as it demonstrates if the lump is intrinsic to the parotid or not.  It also facilitates accurate sampling of the lesion by FNAC or True-Cut biopsy.  Subsequently, CT and MRI are the most useful imaging techniques .
Investigations  Open surgical biopsy is contraindicated unless evidence of gross malignancy is present, and preoperative histological diagnosis is required as a prelude to radical parotidectomy.
Parotidectomy
Parotidectomy  The aim of superficial parotidectomy is to remove the tumour with a cuff of normal surrounding tissue.  The most important structure traversing the parotid gland is the facial nerve.  Parotid tumour excision techniques are classified based on the approach onto the facial nerve.
Parotidectomy  Essentially the traditional parotidectomy is in reality a dissection of the facial nerve. A parotidectomy is  conservative when the nerve is spared ,  radical when the nerve is excised en bloc with the tumour.
Parotidectomy  A superficial parotidectomy is when the part of the gland superficial to the facial nerve is removed.  A deep lobe parotidectomy is when the part of the gland beneath the nerve is removed and  Total parotidectomy is when both are dissected and removed.
Parotidectomy  Superficial parotidectomy can be partial in relatively small tumors that are removed with a cuff of clinically normal parenchyma without removal of the entire superficial portion of the gland.  An alternative surgical approach is to focus on the tumour itself as the principal procedure and not facial nerve dissection.
Parotidectomy  Extracapsular dissection is now an established alternative to parotidectomy.  It does not require formal facial nerve dissection and is a less invasive technique with reduced morbidity.  Temporary facial nerve injury rates are 7% compared with 25% for superficial parotidectomy.
Superficial parotidectomy  Superficial parotidectomy is the most common procedure for parotid gland pathology.  Surgery is performed under endotracheal general anesthesia, which may or may not be accompanied by hypotensive anesthesia to facilitate dissection, improve the visual surgical field and reduce blood loss.  The operation has several distinct phases.
INCISION AND DEVELOPMENT OF A SKIN FLAP  The most commonly used incision is the ‘lazy S’ pre- auricular–mastoid–cervical.  The incision is marked out and three points identified along its length to facilitate closure.  Infiltration with local anesthetic and adrenaline is optional, but does aid in the development of the skin flap, improves visibility and reduces blood loss in the initial phase.
(a) Landmarks and cervical–mastoid preauricular incision for superficial parotidectomy.
INCISION AND DEVELOPMENT OF A SKIN FLAP  The skin flap is developed in an anterior direction by either scalpel or scissors dissection.  The plane of dissection is well below the hair follicles, just above the parotid fascia.  The skin flap is developed forwards to the anterior border of the gland.  Posterior undermining of the incision in the cervical region facilitates access to the anterior border of the sternomastoid muscle.
MOBILISATION OF THE GLAND  This phase of the dissection aims to free the posterior margin of the gland, allowing identification of the facial nerve.  Clips are applied along the fascia overlying the sternomastoid muscle, with the assistant applying traction anteriorly.  By sharp dissection along the anterior border of the sternomastoid, an avascular plane is developed, which requires elective transection of the great auricular nerve.
(b) Development of the avascular plane along the anterior border of the sternomastoid prior to sacrifice of the great auricular nerve.
MOBILISATION OF THE GLAND  At the lower end of the dissection, the external jugular vein is often encountered and ligated.  The gland is gradually mobilized by sharp dissection up to and on to the anterior aspect of the mastoid process, identifying the posterior belly of the digastric muscle.  A second avascular plane is developed along the anterior border of the cartilaginous and bony external auditory meatus immediately anterior to the tragus.
MOBILISATION OF THE GLAND  The two avascular planes are then connected by blunt and sharp dissection.  By developing two broad avascular planes, identification of the facial nerve trunk is facilitated.  It is best achieved by scissors dissection in the line of the facial nerve trunk.  Intraoperative use of a facial nerve stimulator is recommended.
c) Identification of the trunk of the facial nerve (arrow).
LOCATION OF THE FACIAL NERVE TRUNK  The main methods of facial nerve trunk localization can be divided into antegrade and retrograde.  The former utilizes anatomical landmarks to identify the nerve trunk after its exit from the stylomastoid foramen, which is then traced distally.
LOCATION OF THE FACIAL NERVE TRUNK Landmarks commonly used are:  1 the inferior portion of the cartilaginous canal.  This is termed Conley’s pointer (tragal pointer) and indicates the position of the facial nerve, which lies 1 cm deep and inferior to its tip;  2 the upper border of the posterior belly of the digastric muscle.
LOCATION OF THE FACIAL NERVE TRUNK  Identification of this muscle not only helps to mobilize the parotid gland, but also exposes an area immediately superior, in which the facial nerve is usually located;  3 the squamotympanic fissure;  4 the styloid process (the nerve is superficial to it);  5 the mastoid process can be drilled and the nerve identified more proximally.
LOCATION OF THE FACIAL NERVE TRUNK  Retrograde techniques rely on the identification of one of the nerve main branches (buccal in relation to the parotid duct, marginal mandibular in relation to the facial vessels, temporal branch), which is then traced proximally until the main trunk is identified.  These techniques can be useful in revision cases where the anatomy is altered or postradiotherapy when significant fibrosis distorts the planes of dissection.  Once the facial nerve trunk has been identified, gentle traction anteriorly facilitates further mobilization.
LOCATION OF THE FACIAL NERVE TRUNK  Control of hemorrhage at this stage is vital as bleeding, no matter how minor, significantly impedes visibility for the surgeon.  Hemostasis can be achieved with bipolar diathermy, although caution is necessary, particularly as the facial nerve is approached.
LOCATION OF THE FACIAL NERVE TRUNK  Damage to the stylomastoid artery, which lies immediately lateral to the nerve, can result in troublesome bleeding immediately prior to identification.  Pledget swabs soaked in adrenaline are sometimes helpful in reducing the ooze associated with this phase of the dissection.
DISSECTION OF THE GLAND OFF THE FACIAL NERVE  Once the facial nerve trunk is identified, further exposure of the branch of the facial nerve can be achieved by scissors dissection in the perineural plane immediately above the nerve.  The tunnel thus created is then laid open, and divisions and branches of the facial nerve are followed to the periphery in a sequential manner, usually beginning with the upper division.
DISSECTION OF THE GLAND OFF THE FACIAL NERVE  The upper division divides into a temporal and a zygomatic branch, and  the lower division into mandibular and cervical branches.  In this way, the superficial lobe and its associated tumour are mobilized in a superior to inferior direction.
DISSECTION OF THE GLAND OFF THE FACIAL NERVE  The upper division of the nerve is frequently tortuous in its course and it can be damaged unless great care is taken during perineural dissection.  It is often not necessary to dissect all branches of the facial nerve completely, as adequate tumour clearance can be achieved with a more conservative resection of the superficial lobe.
DISSECTION OF THE GLAND OFF THE FACIAL NERVE  When a branch of the facial nerve is adherent to the tumour or running through the tumour, it may require elective division.  With the exception of the buccal branch, the transected nerve should be repaired immediately with a cable graft, harvested from the great auricular nerve.
(e) Branches of the facial nerve and retromandibular vein following delivery of the tumour.
CLOSURE  The patient is placed into a Trendelenburg position to identify any residual bleeding vessels.  A suction drain is applied for a period of 24–48 hours and the wound closed in layers. (f) Wound closure with a vacuum drain.
Extracapsular dissection  Extracapsular dissection is an oncologically sound technique for benign parotid gland tumors.  The recurrent rates of pleomorphic adenomas excision with extracapsular dissection compare favorably with traditional superficial parotidectomies (extracapsular dissection 1.3–1.5% vs superficial parotidectomy 2– 2.4%) and complication rates are less (temporary facial nerve palsy 7% vs 25%: Frey’s syndrome 0 vs 60%)
Extracapsular dissection  A preauricular incision is made, the length and position of which is adapted to the size and site of the tumour.  The dissection proceeds in the plane just immediately above the ‘shining’ parotid fascia (the SMAS or superficial muscular aponeurotic system layer) and continues in continuity with the platysma muscle.
Extracapsular dissection. (a) Left parotid pleomorphic adenoma: skin marking above tumour.
Extracapsular dissection  The skin flap should extend past the lump for at least 1 cm .  The circumference of the tumour is marked with ink and a cruciate incision marked over the surface.  The legs of the cruciate incision should extend 1 cm past the edge of the tumour.  This is an essential part of the technique.
(b) Development of skin flap and exposure of parotid fascia.
Extracapsular dissection  Four small artery clips are then placed where the two lines bisect.  The artery clips are used to tent up the parotid fascia, which is then divided along the cruciate lines.  Small rounded end scissors are then used to commence a dissection through the parotid gland.  The dissection advances in a blunt fashion and only when the scissors blades are visible through the fascia may the tissue bridge be divided.
(c) Cruciate incision through parotid fascia. The leaves of parotid fascia (arrows) have been raised exposing the underlying glandular parenchyma that contains the tumour.
Extracapsular dissection  As the dissection proceeds around the tumour, the presence of a facial nerve is easy to discern.  It is prudent to use continuous facial monitoring during the operation, which helps alert the surgeon to the presence of a facial nerve.  It is not difficult to recognise a branch of the nerve as long as the basic principle is adhered to that no parotid parenchyma is diathermised or cut unless one can see through the tissues. 
(d) Exposure of tumour. The arrow depicts a branch of the facial nerve.
(e) Gradual mobilization of the tumour.
Extracapsular dissection  The key to the extracapsular dissection technique is to place traction on the artery clips, which pulls the parotid tissue away from the lump and normally reveals a plane through which the surgeon can work 2– 3 mm away from the tumour.  When a branch of the facial nerve is observed, it is not necessarily dissected unless in close vicinity to the tumour capsule.
Extracapsular dissection  Retractors can be used on the normal parotid gland to improve exposure of the tumour, but direct pressure on the tumour should be avoided to minimise the risk of rupture.  The tumour is removed ,leaving a parted but essentially intact parotid gland .  Depending on the depth of the tumour, a suction drain can be used at the surgeon’s discretion.
(f) The tumour is mobilized with preservation of the facial nerve branch (arrows).
(g) Excision of the tumour. The picture shows the remaining parotid bed with the facial nerve branch intact (arrows).
Extracapsular dissection  The cruciate incision is re-approximated and the skin incision closed.  It is advised that a mastoid-type pressure dressing is always applied at the end of the procedure otherwise sialoceles can occur.  The pressure dressing is kept for about 48 hours.
(h) The parotid fascia leaves are replaced and sutured together in a watertight fashion. This restores the parotid capsule integrity and prevents development of Frey’s syndrome.
Radical parotidectomy  Radical parotidectomy is performed for patients in whom there is clear histological evidence of a high- grade malignant tumour (e.g. squamous cell carcinoma) with invasion of facial nerve.  Low-grade and low stage malignant tumors can usually be managed by standard superficial parotidectomy.  Radical parotidectomy involves removal of all parotid gland tissue and elective division of the facial nerve, usually through themain trunk .
(a) High-grade malignant tumour in the left parotid gland.
(b) Magnetic resonance imaging scan demonstrating a diffuse infiltrative malignant tumour of the left parotid gland (arrow).
(c) Skin incision outlined for radical neck dissection and left radical parotidectomy including the removal of overlying skin.
(d) Skin flap developed.