Lit. Review
Introduction:
The parotid gland is the largest salivary gland. It is located on each side of the face between the zygomatic arch and the angle of the mandible. It is divided into superficial lobe and deep lobe by the plane of the facial nerve and its branches which pass through it. Salivary gland neoplasms are rare and constitute approximately 3% to 6% of all tumors of the head and neck region(1). Of this, the parotid gland tumors constitute 60-75%. Pleomorphic adenoma is the most common parotid gland tumor(P.G.T) followed by Warthin’s tumor.
P.A.: Most benign tumors can be easily cured by wide local excision, but pleomorphic adenoma, which is the most common salivary gland tumor, has a propensity for local recurrence. Simple enucleation is discouraged.
Depending on the tumor size and location, the conventional superficial parotidectomy(SP) or the more recent techniques like partial superficial parotidectomy(PSP) or extracapsular dissection(ED) maybe performed for resection of benign parotid gland tumors located in the superficial lobe of the gland. The proximity of the tumor to the facial nerve is an important factor in determing the surgical approach. Damage to facial nerve should be avoided and also care should be taken to prevent other complications. The malignant and deep lobe tumors most often require a total parotidectomy(TP) with preservation of the facial nerve.
(28 ref.webpages)-[Minimising damage to the facial nerve is one of the primary objectives of parotid surgery and has encouraged the development of alternative surgical techniques including limited superficial parotidectomy, extra-capsular dissection and selective deep lobe parotidectomy. 18910 ]
Background:
The concept of surgical excision of a parotid tumor was given by Bertrandi in 1802. Initially this surgery involved an extensive approach, causing serious disfiguration and disability(2). In the first half of the twentieth century, the surgery performed was tumour enucleation and had a rapid shelling out of the lump with limited exposure and a high risk of tumor rupture and also there were other forms of subtotal removal.5–7 These approaches were practiced to reduce risk to the facial nerve, and also beacause of a lack of understanding of the biology of these mixed tumours. Recurrence was noted in 23–31 per cent of patients hence treated. (3:3)
In the next half of the twentieth century, the approach to parotid tumors changed. Patey and Thackray recommended superficial conservative parotidectomy to be the standard operation for parotid tumors lateral to the facial nerve. It was reported in the British Journal of Surgery that this standardisation of parotidectomy techniques had revolutionised the surgery of parotid glands (3:10). They were of the opinion that incomplete excision and implantation were the most important factors responsible for the recurrence of primary mixed tumours.(3) Codreanu was the one who performed the first total parotidectomy with preservation of the facial nerve. In 1958, Beahrs and Adson (2:6) described surgical technique of current parotid gland surgery with the relevant anatomy.
The decision to excise parotid lesions are made on multiple factors including obtaining a definitive histological diagnosis, suspicion of malignancy, growth of the lesion or associated discomfort as well as patient preference for removal.(3)
Even though superficial parotidectomy(SP) dramatically reduced the rates of recurrence to 1-4%(31:15), it almost invariably caused many complications like facial nerve paralysis which could be temporary or permanent, loss of parotid function and poor esthetics. The justification for superficial parotidectomy was the concept that the best way to protect the nerve was complete exposure and dissection. Complications like hematoma, sialocele, fistula, Frey’s syndrome, and greater auricular nerve injury, were more frequent after parotidectomy than after enucleation. (2:9,10)
More recently, in the cases of benign and low grade malignant superficial parotid tumors, more conservative approaches are being followed which have lesser aforementioned complications compared to SP or total parotidectomy(TP). These are: 1. Partial Superficial Parotidectomy(PSP) in which only the branches of facial nerve in association with the tumor are dissected and a generous cuff of normal tissue around it is excised, and 2. Extracapsular Dissection(ECD) in which only the tumor with the surrounding minimum small cuff of tissue just outside the capsule of the parotid tumor is excised(5) but in this there is no intentional dissection of the facial nerve. Depending on the loacation and size of the tumor and its proximity to the facial nerve, the preferable approach is opted.
Surgical time is less for PSP and ECD as compared with SP or TP. There is also a higher risk of facial nerve weakness in SP or TP as compared to PSP or ECD.
Parotid gland: surgical anatomy and Facial nerve
(4)-The parotid gland is the largest salivary gland. It is a totally serous gland. Each parotid gland is located in the parotid spaces which surround the posterior part of mandibular rami. Each gland is divided into a superficial lobe and a deep lobe by the plane of the facial nerve which passes through it. The retromandibular vein serves as a radiographic landmark between the two lobes as it is close to the location of facial nerve. There is a dense sheath derived from the submuscular aponeurotic system (SMAS) overlying the surface of parotid. The superficial lobe constitutes approximately 80% of the parotid gland,which is lateral to the facial nerve, antero-inferior to the external auditory canal, and extends down to the angle of the mandible. The remaining 20%, the deep lobe, extends through the stylomandibular tunnel which is formed anteriorly by mandiblular ramus and posteriorly by stylomandibular ligament. The location of a mass in the parotid gland should be defined as superficial, deep, or extraglandular to plan the best surgical approach which can lower the risk of damage to the facial nerve.(4)
The parotid duct or Stensen’s duct arises from the superficial lobe around the masseter muscle and it runs anterior to the buccal fat, where it pierces the buccinator muscle. It then exits the papilla at the buccal mucosa and opens opposite the second maxillary molar.
There is an accessory gland present in approximately 21% of parotid glands(4:3). The accessory gland is located just superior to the main parotid duct, superficial to the masseter muscle. The Stensen’s duct is joined by one excretory duct from the accessory parotid gland. The pathologies that affect the parotid gland can affect the accessory gland. There are several lymph nodes associated with the external surface of the parotid gland, and occasionally a lymph node can be found in the deep lobe as well.
There are 3 important nerves which are related to the parotid gland: the facial nerve, the greater auricular nerve, and the auriculotemporal nerve.(1)
1. Greater auricular nerve is present on the parotid tail. It divides into anterior and posterior branches. It innervates the skin of the face over the parotid gland, mastoid process and near the tragus and the earlobe. It also supplies the sensory innervation to the mass of the parotid gland.
2. The auriculotemporal nerve is a branch of the mandibular division of the trigeminal nerve. It gives the parasympathetic fibers by the otic ganglia to the parotid gland.
3. The facial nerve exits posterior to the styloid process from the stylomastoid foramen.
Facial nerve:
The facial nerve exits the skull at the stylomastoid foramen, posterior to the styloid process, and gives off three branches(48),
1. The posterior auricular nerve. This nerve innervates the auricularis muscle,
2. A branch to the posterior belly of the digastric muscle, and,
3. A branch to the stylohyoid muscle.
Then it penetrates the parotid fascia and enters the parotid gland where it divides into upper zygomatico-facial and lower cervico-facial branches, which in turn terminate into 5 branches:
• temporal branch
• zygomatic branch
• buccal branches which are superficial and deep
• Marginal mandibular branch, and
• cervical branch
Benign parotid tumors(BPT):
Parotid tumors are rare and account for approximately 1% to 3% of all head and neck tumors.(6:1) Of this, 75%–85% are benign.(6:1,2,3) The most common benign and malignant parotid tumors are Pleomorphic adenoma and Mucoepidermoid carcinoma respectively.(6) Neoplasms constitute 75% of all parotid masses, and the remaining are non-neoplastic infiltrative processes like cysts and inflammatory processes. Benign parotid tumors are more likely to occur in females than in males, except for Warthin tumor. Fifth to sixth decade is the predominant age of occurrence, and occurs commonly in Caucasians.
, and size, extent, location and features of the mass. It is very important to know whether the neoplasm is benign or malignant prior to surgery as well as some benign lesions like stones or cysts may not require surgery at times.
Clinical presentation:
Clinical evaluation begins with patient history. Differential diagnosis of a non-neoplastic disease is important. Redness, fever, swelling and elevated WBC count signify an infection(acute or chronic sialadenitis) or obstruction(sialolithiasis). Intraoral examination may identify purulence or calculi at the parotid duct. Benign lymphoepithelial lesions are non-neoplastic glandular swellings associated with autoimmune diseases, like Sjogren’s syndrome.
Benign neoplasms usually present as painless, slow-growing, well-circumscribed, mobile masses. They remain asymptomatic for months to years. Symptoms like pain, fixity, rapid growth, and facial nerve weakness suggest malignancy. Sometimes small, low-grade malignant tumors may present as asymptomatic benign lesion. Hence, fine-needle aspiration should be used when in doubt. It aids in distinguishing benign and malignat tumors.
Diagnostic aids:
WHO classification of benign salivary tumors(6,55):
• Benign epithelial tumors:
o Pleomorphic adenoma
o Myoepithelioma
o Basal cell adenoma
o Warthin tumour
o Oncocytoma
o Canalicular adenoma
o Sebaceous adenoma
o Lymphadenoma:
Sebaceous
Non-sebaceous
o Ductal papillomas:
Inverted ductal papilloma
Intraductal papilloma
Sialadenoma papilliferum
o Cystadenoma
• Soft tissue tumours:
o Haemangioma
o Vascular malformations
o Benign lymphoepithelial cysts
o Lipoma
o Lymph node
o Cystic hygroma
o Congenital anomalies
Ichihara et al(6:21) proposed classification of benign parotid tumors into superficial, deep, and lower pole(region inferior to marginal mandibular nerve) tumors. The lower pole tumors were sub-divided into superficial and deep tumors based on relation to marginal mandibular nerve. These had WT:PA ratio of 2.5:1, more males(ratio 1.6:1), and had on average older patients compared to superficial tumors(57.4 vs 52.2 years). They concluded that for lower pole tumors, identification and preservation of marginal mandibular nerve might be sufficient, without wide dissection. This is different from “true deep lobe” tumors. Hence preoperative localization is important which is possible using CT/MRI.
Pleomorphic adenoma(P.A.)
It is the most common tumor of the salivary glands and represents 45% to75% of all salivary gland tumors. It is also known as benign mixed tumor as it is believed to be derived from both epithelial and mesenchymal components in varying proportions.
They most commonly occur in the parotid gland. Approximately 90% of PA are found lateral to the facial nerve, which, sometimes, may extend to the deep lobe. Remaining 10% are found in the deep lobe. Clinically it presents as a unilateral, painless, mobile, well-demarcated, slow-growing mass. These are more often present in women and middle-aged individuals. Very rarely multiple and/or bilateral PA have been reported. Cut surface has a whitish gray rubbery surface and has a capsule of variable thickness.
(can shorten this)-Histology: PA consists of a mixture of epithelial and myoepithelial components. Epithelial: may be in the form of ducts, nests, cords, or solid sheets of cells. myoepithelial: cells that appear plasmacytoid or spindled in a fibrocollagenous, myxochondroid, or chondroid background. This is considered to be responsible for the characteristic myxoid or chondroid stroma.
Almost all pleomorphic adenomas have focally thin capsules, and 1/4th of them demonstrate satellite nodules or pseudopodia. These pseudopodia are believed to be one of the reasons for recurrence, another being tumor spillage. Hence a wider excision is preferred for PA. But recent studies have demonstrated limited parotidectomy to have similar recurrence rates to wider excision.
Recurrence, if occurs, is challenging to manage. It can occur 5-7 years after primary surgery. Malignant transformation can occur in 3% to 15% of PA and risk increases with observation, therefore surgical excision at the time of diagnosis is preferrable.
Myoepitheliomas
Myoepitheliomas are rare benign salivary tumors (1.5% of all salivary tumors and 0.8% to 3.4% of benign parotid tumors(6)). These are homogenous, white, well demarcated, with a smooth surface. Microscopically, represent one end of the spectrum of mixed tumor in which ductal structures are extremely rare to absent. They are composed of predominantly spindle cells, epithelioid and clear cells may also be present.
Clinical features are similar to pleomorphic adenomas. No gender predilection has been noted. The majority of these neoplasms behave in a benign manner, malignant transformation has been reported.
The treatment is surgical excision.
Basal Cell Adenomas
Basal cell adenomas constitute approximately 2.4% to 7.1% 2,3,36 (6)of benign parotid tumors. They occur more commonly in women and in 4th to 9th decades of life. They are 3rd most common tumors after PA and WT. They present as a slow-growing, asymptomatic mass similar to other benign neoplasms. Its a well-circumscribed, solid tumor with a gray-white to pink-brown cut surface. Parotid basal cell adenomas are encapsulated and histologically characterized by basaloid appearing epithelial cells. Four histologic subtypes have been identified: 1) solid, 2) trabecular, 3) tubular, and 4) membranous.
The treatment is surgical excision with a cuff of normal surrounding tissue.
Papillary Cystadenoma Lymphomatosum: Warthin Tumors or adenolymphoma
(doubtful abt edit, that is, plagiarism;find out this reference source)
It was first described by Aldred Warthin in 1929. Warthin tumor constitutes 25% to 32% of benign parotid tumors and is the second most common benign salivary gland neoplasm after pleomorphic adenoma. It is found almost exclusively in the parotid gland, more commonly in males(ratio 2:1) as it is associated with cigarette smoking and is more prevalent in Caucasians. Compared to other benign tumors, WT presents in older population (50-60years of age) and 5-12%% of the time it occurs bilaterally.(6)
Clinically, WT presents as an asymptomatic, slow-growing mass often in the tail of the parotid gland at the angle of the mandible. These are usually ovoid encapsulated masses and have a smooth or lobulated surface. On sectioning, its commonly cystic containing mucoid, brown fluid.
Microscopically, WTs contain lymphoid tissue and eosinophilic epithelial papillae that project into cystic spaces. The cystic lining is arranged in two layers of cells and the cystic lumen may contain thick secretions or cellular debris.
Technetium scans can aid in the preoperative diagnosis, as WTs concentrate this isotope and give the appearance of a “hot gland”. FNAB shows a mixture of mature lymphocytes and oncocytic-appearing epithelial cells. WT doesn’t show malignant potential.
Treatment is surgical excision but the extent is debated as there are reports of recurrence.
Oncocytoma (Oxyphilic Adenoma, Oncocytic Adenoma)
Oncocytoma constitutes less than 1% of all salivary gland tumors. This is a benign neoplasm of the oncocytes that arises most commonly in the parotid gland. Oncocytic cells can also be seen in other benign and malignant salivary pathologies.
Usually presents in the fifth to sixth decade of life at the time of diagnosis and gender distribution is almost equal. Oncocytomas are painless, slow growing tumors that are well circumscribed, lobulated and encapsulated and may have an orange or red hue. Histologically, the tumor has a granular appearance because of abundant hyperplastic mitochondria. It shows an increased uptake for pertechnetate and hence can be seen on radionuclide scans.
Treatment of is surgical excision. It has a good prognosis. Malignant transformation is rare.
Management of benign parotid gland neoplasms:
Tumors of the parotid gland should be removed completely. They are generally removed with an adequate cuff of surrounding normal tissue. The facial nerve is carefully dissected and preserved. The extent of facial nerve dissection and the amount of resection of parotid tissue depends on the location, size, and histology of the tumor. 98
Small tumors that are located in the parotid tail may require dissection of only the lower division of the facial nerve, saving the upper division from unnecessary dissection. The tumor is removed with the surrounding parotid tissue.
For larger tumors of the superficial lobe, a complete superficial parotidectomy is usually required. Deep-lobe tumors require excision of the deep lobe with careful preservation of the facial nerve. Parapharyngeal tumors are most commonly excised through a cervical-parotid approach. 99
Diagnostic aids:
Ultrasonography(USG):
USG is an effective tool to distinguish between cystic and solid tumors, and also for characterizing anatomy of superficial lobe tumors. Its disadvantage is that it cannot properly visualize deep lobe tumors or facial nerve. Benign neoplasms are usually hypoechoic with smooth margins. PA are distinguished from WT by poor no vascularization, whereas WT are hypervascular. PA have lobulated contour, acoustic enhancement posteriorly, and sometimes, internal calcification. WT usually conatin anechoic cystic areas internally.
CT and MRI:
Computed tomography(CT) and Magnetic resonance imaging(MRI) provide excellent anatomic information because of high fat content of the parotid gland. CT and MRI help in evaluating the relationship of the tumor to the gland or adjacent structures, including bone and soft tissues. CT aids in evaluating the location of stone in case of sialolithiasis, or the magnitude of infection and presence of abscess in case of infections, and also helps in distinguishing solid and cystic lesions.(56) The distinction between benign and malignant lesions is poor on CT.
MRI is more sensitive in distinguishing neoplasms and it best displays the spread to adjacent soft tissues or perineural spread.(cumming’s). One advantage of MRI scan is the ability to likely diagnose pleomorphic adenoma when a hyperintense and well localized mass is noted on T2-weighted image(52). In case of Warthin tumor, there is a heterogenous signal on T2-weighted image with bright signal in areas of cyst formation.
CT and MRI are effective in evaluating the size, extent and location of the tumor, but they are poor on their own in diagnosing individual histologies, and distinguishing between benign and malignant lesions.
Fine needle aspiration biopsy(FNAB):
FNAB is a very important diagnostic tool for differentiating benign and malignant tumors. It helps the surgeon in counselling the patient and planning for extensive dissection and cervical lymph node dissection, in cases of malignancies. Also, it saves the patient from unnecessary surgery by differentiating inflammatory and neoplastic conditions. The sensitivity and specificity of FNAB ranged from 84% to 74% and 98% to 88%, respectively(52:16.20,19).
Image-guided FNAB may be needed for clinically non-palpable tumors and tumors located deeper. In cases where FNAB was non-diagnostic, ultrasoung or CT-guided core needle biopsy(CNB) can be used as an alternative. According to recent studies(6:31), CNB is safer and more accurate than FNAB, especially in cases of malignant tumors.
Nuclear imaging:
Nuclear imaging is useful in confirming the diagnosis of Warthin tumors and Oncocytomas as these have increased uptake of pertechnetate. They appear as “hot nodules” in radionuclide scans. This is helpful in differentiating Pleomorphic adenoma from WT in patients with surgical contraindications.(cumming’s:6)
Sonoelastography:
This new technique is still under investigation. A mechanical force is applied(with a probe) after which ultrasound is used to measure the deformation of tissues. It can be used to differentiate between different histologies of parotid tumors.(6:32)
Hence, in cases of parotid tumors, a thorough patient history, clinical examination and preoperative diagnostics tests should be carried out before proceeding to the surgical management.
Surgical management:
The goal of a parotid tumor surgery is to completely remove the tumor so as to reduce the risk of recurrence, and to preserve the function of facial nerve and its branches. For a benign parotid tumor located in the superficial lobe of the parotid gland, the surgical trends that are in current practice are:
Superficial parotidectomy(SP):
SP is considered to be standard procedure in treatment of benign parotid tumors. In this, anterograde dissection of the entire course of the facial nerve(FN) is carried out, and the whole of the superficial lobe along with the tumor is removed “en bloc”.
The standard incision is an ‘S’ shaped curvilinear incision(modified Blair incision). It begins in the preauricular skin crease and curves around the ear lobe and mastoid process and extends to the cervical skin crease. Depending on the extent and location of the tumor, the incision maybe modified appropriately. The skin flap should be elevated in a plane superficial to the parotid capsule. The anterior flap is raised till the masseter muscle, and the posterior flap is elevated until the mastoid process and posterior portion of sternocleidomastoid is exposed. Injury to the peripheral branches of facial nerve can be avoided by staying close to the skin.
The greater auricular nerve is seen first running from posterior border of sternocleidomastoid(SCM) muscle to pinna, parallel to the external jugular vein and is divided or retracted. Dissection is continued, separating the posterior edge of the parotid gland from SCM, and superiorly from the external auditory canal. This sharp dissection is continued until the tragal pointer is identified. FN is located deep to this point. Blunt dissection is continued till the junction of posterior belly of digastric and SCM is identified. The main trunk of the FN is located approximately 4mm superior and parallel to this junction(52).
After identification of the main trunk of FN, careful dissection is carried out on its surface. Bifurcation of the FN is noted. Blunt dissection of the entire course of the facial nerve is done carefully, separating the entire superficial lobe along with the pseudocapsule, and excising it. The dissected facial nerve is entirely preserved with all its branches remaining intact. Absolute hemostasis must be achieved before closure of the wound begins. Suction drain is placed and the wound is closed in two layers. Sterile gauze dressing is placed.
Locoregional parotid reconstruction(58,59):
After total, superficial, or partial parotidectomy, patients are usually left with a cosmetic defect which causes disfigurement and decrease in the quality of life of the patient. The goal of reconstruction is to prevent Frey’s syndrome, correct any facial nerve abnormality, and improve esthetics by restoring the facial contour. The different types of flaps used in reconstruction are:
• SCM muscle flap, which can be superiorly or inferiorly based. It is the most commonly used flap. Can be used with or without acellular dermis.
• Superficial muscular aponeurotic system(SMAS) flap: used for small defects. Can also be used in conjunction with SCM flap.
• Temoroparietal fascial flap: based on superficial temporal artery. Used for defects larger than 3cm. can be used as interposition flap.
• For larger defects, supraclavicular artery island(SAI) flap, and Anterolateral thigh(ALT) free flap can be used.
• Cervicofacial advancement flaps are used where tumor involves the overlying skin
Identification of facial nerve:
Surgical landmarks of the facial nerve include: (21)
1. The tympanomastoid suture line, it is a palpable hard ridge which is deep to the cartilaginous part of the external ausitory canal. The facial nerve lies 2-6mm deep to it
2. The tragal pointer, it is considered as the most important landmark. Facial nerve lies approximately 1cm deep and inferior to it. As the tragal cartilage is dissected free from the parotid fascia, its medial aspect acts like a blunt “pointer”. The disadvantage is that it is mobile, assymetrical and blunt.
3. Posterior belly of the digastric muscle. It is deep to the sternomastoid. Lateral retraction of sternocleidomastoid muscle exposes the posterior belly of digastric. Facial nerve is located approximately 1cm above the digastric near its insertion at the mastoid tip
Facial nerve can also be identified by retrograde dissection of one or more peripheral branches of the nerve or by using a facial nerve monitor.
PSP:
In this technique, parotid tumor with the associated part of the gland is removed and facial nerve only in the vicinity of the tumor is dissected. There are two approaches of dissecting the FN for this technique: anterograde and retrograde.
For anterograde dissection of the FN, same steps are followed as SP, till the main trunk of the facial nerve is identified and then the dissection of the branches is continued depending on the location of the tumor. Only those branches in relation to the tumor are dissected, the remaining branches are protected.
For retrograde dissection, a standard ‘S’ shaped preauricular incision is made according to the size and extent of the tumor. The skin flap is raised to the superior, anterior and inferior borders of the gland. The peripheral branch or branches of the facial nerve are identified first and then retrograde dissection of the nerve is done, the extent of which depends on the size and extent of the tumor. The remaining branches are protected and the main trunk of the facial nerve doesn’t have to be intentionally identified.
For both of these, the tumor is removed along with the corresponding healthy part of the gland, usually a rim of 1-2cm. Hemostasis is achieved, layered suturing is done, and a suction or pen-rose drain is placed.
Anatomic landmarks for branches of the facial nerve (11):
Buccal branch: runs parallel to the Stensen duct and divides into two branches, running upward and downward along the duct.
Marginal mandibular branch: it extends anteriorly and inferiorly within the parotid gland. It crosses superficial to the retromandibular vein and it may have 3 branches.
Zygomaticotemporal branch: it crosses the zygomatic arch 8 to 35mm anterior to the anterior concavity of the bony external auditory canal, and superficial to the superficial fascia of the temporal fascia.(11)
In a study of 363 PSP’s conducted by O’Brien(52:24), the incidence of temporary and permanent facial nerve weakness was found to be 24% and 2.5% respectively. Recurrence was reported in 0.8% of the patients. He concluded that for tumors located in the superficial lobe, the treatment of choice is PSP. He also indicated that PSP can be performed for excision of most superficial lobe malignant tumors. Lim et al(52:25) reviewed 43 cases of superficial lobe malignant tumors treated by PSP. The overall survival rate and disease-free rate at 5 years was 88% and 79%, respectively. Recurrence occurred in 6 high-grade(n=16) and 2 low-grade(n=27) cases. They concluded that PSP “with appropriate postoperative radiotherapy may be an acceptable procedure in the treatment of low-grade parotid cancers confined to the superficial lobe if the facial nerve is sufficiently distant from the tumor.”(52:25)
In a comparative study of 101 patients with benign tumors(52:26), 52 underwent PSP with 0.5 to 1cm tumor-free margins, and 49 underwent SP or total parotidectomy(TP). Early complications were observed in 40% PSP and 100% SP or TP patients. Temporary facial nerve weakness was significantly more frequent in SP or TP group. During a 4-year follow up period, no recurrences were noted ineither groups. Hence they justified PSP technique in the removal of benign parotid tumors.
ECD:
In this, the parotid tumor is dissected immediately outside the tumor pseudocapsule without intentionally identifying or dissecting the trunk or branches of the facial nerve unless the psedoucapsule is in close proximity to any of the branches.(14)(25) This is the most conservative and practical approach in the surgery of benign parotid tumors.
The standard pre-auricular incision ‘S’ shaped incision is given. The incision can be modified depending on the size and extent of the tumor. The skin flap is raised immediately superficial to the parotid fascia. Then the borders of the tumor are marked with ink. Incision is given atleast 1cm from the edges of the tumor to have a good access. Care should be taken to avoid injury to the greater auricular nerve. The normal parotid tissue is retracted away. It reveals loose tissue planes and 2-3mm of tumor capsule. Finding a safe plane of dissection is the key to ECD. Good hemostasis is very essential. Tumor pulling has to be avoided to reduce the chances of capsule rupture. As dissection continues deeper, slow dissection is done and proximity to facial nerve branches can be evaluated with the help of a nerve stimulator. After the resection of tumor, the parotid fascia is sutured back. This prevents the loss of contour seen in SP or sometimes PSP and also eliminates dead space. Also, this will eliminate the chances of Frey’s syndrome. A suction or Penrose drain is placed and the skin is closed in 2 layers.
The safety margin of ECD, especially in cases of Pleomorphic adenoma has been debatable. Some authors(57:4) insist a 2cm safety margin for PA, while others(57:3) state that a thin connective tissue margin is sufficient for safe removal and minimum recurrence rates. Resection of the tumor directly adjacent to tumor capsule is unavoidable in 30% of the cases(57:5). According to the literature, there is no significant difference in the recurrence rates among different techniques.(57:5,8). Infact, tumor spillage plays a more important role in recurrence. No recurrences have been reported in a study of 67 PAs operated by ECD, over a mean follow-up period of 7.4 years.(57:7). The rates of postoperative complications after ECD are significantly lower as compared to SP(57:8,9,10). ECD provides favourable esthetic results. As most of the healthy parotid tissue remains in place, there is no major difference between healthy and operated sides. In cases of recurrence, the patient who had initially been operated by ECD is at an advantage than the one operated by conventional parotidectomy.(57) ECD cannot be applied for malignant or deep lobe tumors. Ideal conditions are small, benign tumors in the parotid tail. Tumors in the superficial lobe can also be removed by ECD by experienced surgeons. Care has to be taken to prevent rupture of the tumor capsule. Intraoperatively, the technique of ECD might have to be shifted to formal parotidectomy, hence the surgeon has to be practically well experienced in conventional parotidectomy. FNAB should routinely be used for preoperative confirmation of benign nature of the tumor, in case of ECD
Complications of parotidectomy:
More often than not, parotid surgery if followed by complications. The goal of the surgery is to minimise complications as much as possible. Despite this, complications do occur in some cases. The frequency of complications, in general, is proportional to the degree of invasiveness of the surgery.(57)
General
• Hemorrahge or hematoma
• Seroma
• Infection
• Necrosis of skin flap
• Hypertrophied scar
Specific
• Facial nerve weakness(temporary or permanent)
• Frey’s syndrome
• Greater auricular nerve weakness
• Salivary fistula or sialocele
• Cosmetic deformity
• Recurrence
Table 1 Complications of parotid gland surgery
Facial nerve weakness:
The risk of facial injury is proportional to the length of the nerve dissected. Facial nerve paresis depends on the length of the facial nerve dissected. Hence rate of facial paresis after conventional SP is higher than after limited parotidectomy or ECD. Weakness can affect just one or many branches. Marginal mandibular branch is the most commonly affected as its longer and very sensitive, leading to temporary weakness of the lip. This usually improves in 4 to 6 weeks(13). If the nerve function returns within 3-6 months, it is considered as temporary facial paresis. This can sometime take upto one year. In some cases, there is permanent facial paralysis, where the nerve function doesn’t return to normal. For severe facial nerve damage, reconstruction can be done using nerve grafting.
In a study of 894 patients(17), 395 ECDs and 499 SPs were performed. The rate of temporary facial palsy after SP was 10.6% which lasted for 35.1 days, and after ECD was 11.4% which lasted for 36.7 days. After a one-year follow-up, 9 patients after ECD and 3 patients after SP, had facial palsy.
The facial nerve function can be graded using House-Brackmann grading system. It ranges from Grade I normal to Grade VI total paralysis.
Frey’s syndrome:
This is believed to be caused due to abnormal regeneration of parasympathetic fibers of parotid gland, which, instead, connect to the subcutaneous sweat gland. Post surgically the surface of the parotid is left exposed to subcutaneous tissue; as a result this abnormal regeneraton occurs. In cases of conventional parotidectomy, reconstruction of the parotid defect using SCM or SMAS flap, helps prevent Frey’s syndrome to a great extent. Acellular dermis(AlloDerm) is also used in minor defects.
For ECD, there is not much defect left post-surgically. Suturing the parotid capsule back together prevents Frey’s syndrome.
In a study of 349 patients(29), 44% from the SP group, and 1.3% from the ECD group developed Frey’s syndrome. Management of Frey’s syndrome includes reassurance of the patient, use of anti-cholinergics or benzodiazepenes; if there is no improvement then Botulinum toxin injections can be given. Radiotherapy can also be used.
Greater Auricular nerve weakness:
The GAN enters the parotid fascia at the tail of the parotid. For tumors present in the parotid tail, preservation of GAN is difficult. GAN can be preserved about 60% of the time[21ref.website]. Injury or sacrifice of the GAN causes dysesthesias of the cheek and earlobe. This is usually temporary.
In a study of 377 patients treated by ECD, GAN weakness was found to be the most common complication, occurring in 10% of the cases. 5% developed seroma, 3% hematoma, and 2% developed salivary fistula.
Recurrence:
Rate of recurrence after enucleation was very high(20% to 40%). Introduction of superficial parotidectomy reduced these recurrence rates to 1% to 4%. Presently, there is no significant difference in the recurrence rates of SP, PSP or ECD, according to the literature.(references). Pleomorphic adenoma is the most prone to recurrences. This is due to its histology, containing satellite cells and pseudopodia. Recurrence is believed to be due to intraoperative tumor spillage, rather than the extent of resection.
In case of recurrence, patient who had initially been operated by ECD is at an advantage than the one operated by SP.
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