Parotid Dissection (Cadaver)
Main Text
Table of Contents
Salivary gland tumors (SGT) are a relatively uncommon and morphologically diverse group of neoplasms, with an average annual incidence rate of 2.5–3.5 per 100,000.1 The majority of these tumors (approximately 80%) occur within the parotid gland (PG), which is the largest of the salivary glands.2 Interestingly, over 80% of PG tumors are benign in nature, with the most common pathologies being pleomorphic adenoma and Warthin's tumor.3
The treatment options for PG tumors depend on the nature of the tumor, whether it is benign or malignant. PG surgery has experienced a significant evolution in the last 20 years. While superficial parotidectomy (SP) was previously the standard of care at many centers, other operative options such as extracapsular dissection (ECD) and partial superficial parotidectomy (PSP) have gained popularity more recently.4,5
During the SP procedure, the affected region of the PG is surgically excised, while taking care to identify, preserve, and dissect away the facial nerve. The facial nerve emerges from the stylomastoid foramen before entering and branching throughout the PG, delineating the superficial and deep lobes of the gland. Regardless of the extent of parotid surgery, it is imperative to locate and carefully dissect the facial nerve to prevent iatrogenic injury and maintain normal facial nerve function.
Detailed preoperative evaluation is crucial, as different histological types of benign parotid tumors may require varying interventions. Pleomorphic adenoma and Warthin's tumor account for the majority of benign cases and often necessitate distinct surgical approaches.6 However, accurately diagnosing the malignant potential of a parotid mass preoperatively can be challenging, as fine-needle aspiration (FNA) and imaging studies do not always provide a definitive diagnosis.7 The sensitivity and specificity of PG FNA cytology depend on the operator’s technique, the quality of the specimen, the pathologist’s experience, and the presence or absence of cystic components.8–12 Therefore, surgeons must be prepared to escalate the procedure to a total parotidectomy if intraoperative findings indicate a malignant tumor. For example, despite the benign nature of certain PG lesions, complete surgical removal of the entire gland may be warranted in specific cases. This is because particular pathologies affecting the parotid demonstrate an elevated likelihood of recurrence if any remnant glandular tissue is left behind after the initial surgery.13
In cases of malignant tumors, a more extensive approach, such as total parotidectomy, is required. This procedure involves the removal of the entire PG, including the deep lobe, to ensure complete excision of the tumor. Surgical removal of the deep part of the PG is a complex procedure involving careful management of blood vessels within the gland, deeper facial vessels, and repositioning of the facial nerve main branch.14 The incision for a total parotidectomy is often larger and may extend into the hairline or neck, depending on the extent of the disease.15
The decision between superficial and total parotidectomy is made based on the preoperative evaluation, including imaging studies and FNA results, as well as intraoperative findings during the dissection. This detailed video provides an overview of the parotid dissection procedure, including the incision, raising of the flap, identification of key anatomical landmarks, and the dissection of the deep lobe of the PG.
The procedure is conducted under general anesthesia, with the endotracheal tube secured on the contralateral side. It's important to inform the anesthesia team to refrain from using muscle relaxants to allow for monitoring of facial nerve function. The neck is gently extended, and the head is turned away from the side being operated on. This procedure is typically performed through an incision within a natural skin crease or using a "gull-wing" approach to minimize scarring and optimize cosmetic outcomes.16 The choice depends on factors like postcontraction distortion and scar visibility. Following the incision of the dermis and platysma, an anterior skin flap is elevated between the superficial musculoaponeurotic system (SMAS) and the superficial capsule of the parotid. It is recommended to raise a thick flap to reduce the risk of Frey's syndrome and skin necrosis. The SMAS flap can be reattached to mitigate cosmetic deformity and reduce the risk of Frey syndrome. Particular attention is paid to avoid damaging the great auricular nerve and preserving its posterior branch if circumstances permit.17,18 The most challenging aspect of elevating the flap is the presence of the dense connective tissue band.
Subsequently, the parotid fascia is separated from the perichondrium of the cartilaginous canal of the external auditory meatus. The next step involves exposing it to the level of the tragal pointer. The tragal pointer serves as the first landmark, and the areolar appearance of the tissue around it guides the depth of the incision. The tragal pointer is identified, and the area around it is carefully cut through, ensuring not to go too deep.19 The location of the facial nerve lies around 1 cm deep and inferior to the pointer within the PG unless influenced by tumor presence or distortion.
Next, the focus shifts to locating the posterior belly of the digastric muscle. Initially, the tissue is observed, and the external jugular vein is identified and subsequently dissected. Upon tissue elevation, the posterior belly of the digastric muscle becomes visible. Once the the posterior belly of the digastric muscle is identified, the dissection becomes considerably easier, allowing for the removal of the surrounding tissue. Upon reaching the level of the the posterior belly of the digastric muscle and the tragal pointer, the tympanomastoid suture can be palpated as a hard ridge deep to the cartilaginous portion of the external auditory canal.
The next step involves traversing through the parotid fascia to ensure visibility. Continuing the dissection, a structure is encountered that is difficult to discern whether it is an artery or nerve, particularly in cadaveric specimens. The location aligns with where the nerve is expected to be, suggesting it may indeed be the facial nerve. By tracing the structure forward, its identity becomes clearer, indicating it is likely the facial nerve.
At this juncture, the surgeon should be prepared to commence the delicate and meticulous task of facial nerve dissection along its branches. It is important that dissection be performed directly atop the nerve, ensuring constant visualization. The parotid tissue overlying the dissected area of the facial nerve should be divided, never extending beyond that region. During the process, the retromandibular vein is frequently encountered deep to the facial nerve. When removing the superior portion of the gland, ligation of the superficial temporal artery may become necessary. Upon removal of the deep parotid lobe, the superficial lobe can be completely excised by the surgeon. Branches of the facial nerve should be released from the tissue of the deep lobe via a combination of blunt and sharp dissection techniques. If this proves challenging or inadequate, the transcervical approach with division of the stylomandibular ligament provides excellent exposure of the parapharyngeal space, which encompasses the deep parotid lobe.
Attention is drawn to the external carotid, deep transverse facial, superficial temporal arteries, and the retromandibular and superficial temporal veins, often overlooked vessels that must be identified and controlled. Once these vessels are managed, the deep lobe of the PG can be freed from the styloid process.
Parotid dissection is a delicate surgical procedure that requires a deep understanding of the relevant anatomy and a careful approach to ensure the preservation of critical structures, particularly the facial nerve. The comprehensive overview provided in this video is a valuable resource for understanding the step-by-step process of parotid dissection. The detailed narration and visual references help to reinforce the importance of accurate identification and preservation of the facial nerve, as well as the other key anatomical structures involved in the procedure. This information is crucial for surgeons in training, as well as for experienced practitioners, to ensure the safe and effective removal of PG tumors while minimizing the risk of complications.
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Citations
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- Bussu F, Parrilla C, Rizzo D, Almadori G, Paludetti G, Galli J. Clinical approach and treatment of benign and malignant parotid masses, personal experience. Acta Otorhinolaryngol Ital. 2011;31(3).
- Bradley PJ, Guntinas-Lichius O. Salivary gland disorders and diseases: diagnosis and management. Ann Royal College Surg Engl. 2013;95(6). doi:10.1308/rcsann.2013.95.6.450.
- Roh JL, Kim HS, Park CI. Randomized clinical trial comparing partial parotidectomy versus superficial or total parotidectomy. BJS. 2007;94(9). doi:10.1002/bjs.5947.
- O’Brien CJ. Current management of benign parotid tumors - the role of limited superficial parotidectomy. Head Neck. 2003;25(11). doi:10.1002/hed.10312.
- Kawata R, Kinoshita I, Omura S, et al. Risk factors of postoperative facial palsy for benign parotid tumors: outcome of 1,018 patients. Laryngoscope. 2021;131(12). doi:10.1002/lary.29623.
- Taniuchi M, Terada T, Kawata R. Fine-needle aspiration cytology for parotid tumors. Life. 2022;12(11). doi:10.3390/life12111897.
- Tyagi R, Dey P. Diagnostic problems of salivary gland tumors. Diagn Cytopathol. 2015;43(6). doi:10.1002/dc.23255.
- Song IH, Song JS, Sung CO, et al. Accuracy of core needle biopsy versus fine needle aspiration cytology for diagnosing salivary gland tumors. J Pathol Transl Med. 2015;49(2). doi:10.4132/jptm.2015.01.03.
- Rossi ED, Wong LQ, Bizzarro T, et al. The impact of FNAC in the management of salivary gland lesions: institutional experiences leading to a risk-based classification scheme. Cancer Cytopathol. 2016;124(6). doi:10.1002/cncy.21710.
- Colella G, Cannavale R, Flamminio F, Foschini MP. Fine-needle aspiration cytology of salivary gland lesions: a systematic review. J Oral Maxillofac Surg. 2010;68(9). doi:10.1016/j.joms.2009.09.064.
- Ahn S, Kim Y, Oh YL. Fine needle aspiration cytology of benign salivary gland tumors with myoepithelial cell participation: an institutional experience of 575 cases. Acta Cytol. 2013;57(6). doi:10.1159/000354958.
- Aro K, Valle J, Tarkkanen J, Mäkitie A, Atula T. Repeatedly recurring pleomorphic adenoma: a therapeutic challenge. Acta Otorhinolaryngologica Italica. 2019;39(3). doi:10.14639/0392-100X-2307.
- Karp EE, Garcia JJ, Chan SA, et al. The role of total parotidectomy in high-grade parotid malignancy: a multisurgeon retrospective review. Am J Otolaryngol Head Neck Med Surg. 2022;43(1). doi:10.1016/j.amjoto.2021.103194.
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Cite this article
Brown CS, Esclamado RM. Parotid dissection (cadaver). J Med Insight. 2024;2024(161.5). doi:10.24296/jomi/161.5
Procedure Outline
Table of Contents
- Malignant Tumor
- Benign Tumor
- Dissect Great Auricular Nerve
- Dissect Above Band of Dense Connective Tissue
- Expose Tragal Pointer
- Identify Artery
- Identify Facial Nerve
- Follow Superficial Temporal Vessels
- Identify Lower Division
- Mobilize the Nerve
- Control Superficial Temporal Vessels
- Find Terminal Branch of External Carotid
- Dissect Parotid from Posterior Border of Mandible
- Free Deep Lobe from the Styloid
Transcription
CHAPTER 1
The first thing to think about is your incision. You basically have four things to think about. One is cosmesis. You can do an incision in a crease here. I try to do a little “gull-wing” - just you want to have a straight line that shortens. And then around the ear, I like to make a point, so as that contracts, you don't get pulling up of the ear like that. Now if you really want to hide the incision, you can do it as a facelift, which you can go way back here and into the hairline and then elevate a real broad flap like that - shave the hair a little bit. That's - this works if you have a posterior lesion here. Tumor’s up there. Your exposure’s going to be a little bit worse, but it's a nice way to do it, particularly in women who have - wear their hair long; you can shave a little hair and the - the scar is basically imperceptible. The other option is taking it down into a crease like this, and the decision of how far to go depends on whether or not you're going to incorporate a neck dissection. So if you’re going to do a neck, you may want to take it down in here. If you're going to do a parotid, you can even just limit the incision in a crease. You’re pretty limited there. So that's the first thing. The next thing is your plane of dissection and raising your flap. If you - if your tumor is - so you got to point here - if your tumor is on this - is on the capsule or near the capsule of the gland and it's malignant, I like to raise the fat, the plane, above this mass. So if you do that, you're going to want to see the bottom of the hair follicles in your flap. If it's benign and the tumor’s deep in the gland, I prefer to save this mass. I don't know whether that helps with the postoperative Frey’s or anything like that, but it also gives you a little bit of thickness.
CHAPTER 2
The other topographical anatomy is you got to be aware of are the great auricular nerve. It runs behind the EJ and about halfway between the mastoid tip and angle of the mandible. If you can and you don't have a tail or parotid lesion, you can dissect the nerve up and save the posterior branch, which will preserve some sensation. If you just dissect it all the way up, you're going to leave a little bit of - you’re going to leave a little bit of parotid here as you preserve the nerve, but that's okay as long as the tumor’s not nearby. The hardest place in elevating this flap is right here because there's a - there's a dense connective tissue band there that - that you don’t really - you can't see the plane, but the key is is just to stay on top of it. I think I’m beneath - this is that connective tissue band here. You can barely see it, but I think I'm on top of the this mass here - below this mass here. Okay so - so there’s fat, and I’m deep to mass. Okay, then you can take it right to the front end of the gland. Just want to raise this back a little bit - just so you can identify the EJ, and... And this is going to get you your exposure. There.
CHAPTER 3
So the next move is to separate the parotid fascia from the perichondrium of the external auditory cartil - the cartilaginous canal, and when you dissect, that's a - usually - a very easy plane to get into. It's a kind of a wispy plane, and if you're in it, it will spread pretty easily. You can see that there is a plane here. Okay? So now you want to just expose it to the level of the tragal pointer. Okay, that's your first landmark. Your three landmarks are your tragal pointer - you see that nice areolar plane there? That's where you want to be, okay? So there’s your tragus right there, and just cut down through there, Kevin. Let’s see - you don’t want to get too deep. Okay, so you got to expose that whole tragal pointer, which is - you can see it there. It comes into a point, okay? That's the tip of it. So the location of the facial nerve is 1 cm anterior and inferior to the tragal pointer unless there's a tumor pushing it up from below - a deep lobe tumor - or it’s being distorted by the tumor. That’s usually where it is. The key is there - it is in the parotid gland, okay? So to get there, you've got to cut the fascia of the parotid. The other way to do it is to follow the tympanomastoid suture line. That, in the books, they say that is the most consistent landmark that you can follow - the tympanomastoid suture line down to the stylomastoid foramen. I don't like to do that personally because I just feel like it's too deep. The nerve is going to cross the parotid fascia, so you won't even have to get into the parotid. You can just dig down there and get to it, but it’s a - tends to be a deep hole down there. So I - that's - I don't know who does it - if the other - my esteemed colleagues do it that way, but I don't like to do it unless forced.
CHAPTER 4
So the next point here is you got to find the digastric tendon, right? So this looks like a CM to me and some wonderful tissue planes. That's probably EJ there - going to cut it. So you got to elevate this off. There's digastric there, okay? Then you can just follow this digastric, and there’s only one thing that crosses the digastric, which is the common facial vein, anteriorly. And once you got the digastric, you can now do this dissection here very easily until you get all of this removed. Okay. And when you get to level of the digastric and the tragal pointer, which is here, you can feel the tympanomastoid suture, which is right there. Okay, then what you have to do is - now you know that the nerve is going to be about here, right? About a centimeter anterior and inferior - and it's going to be at the level of the digastric in the parotid.
CHAPTER 5
So the next move here is actually to go through the parotid fascia and just make sure that you can see everything, and I'll probably cut the nerve here but… Okay, so this just - oh see I just - did you see that fascia I just cut? It's all parotid fascia that's going to... Okay. So, it should be about right here, and all this is fascia, which you cut. Now there’s usually an artery that lives above that. I'm - I’m not sure what that artery is called. Does anyone know the name of it? I think it's right there. And that'll be a bother. It's always there. Okay. And that should - this should take you right to the nerve. I don't know if that's it or not. Okay, it’s either that, or it’s the artery. So there's a structure here. In the cadaver, it's hard to tell whether it’s an artery or nerve, but - see that? It's kind of right where it should be. You can follow it forward a little bit to see if it is it. Okay. Looks like that's it. Okay, so that's probably the facial nerve there. Is there anything below there? No. Here’s the artery above it, okay? So this is probably lower division here. The pes, yeah.
CHAPTER 6
So, now, the tendency here is - is to just - once you see that, is to start cutting everything above it, but remember - it's a lateral dissection, so you want to make all your cuts inferiorly or superiorly. I've had most trouble with superior with the upper division and that forehead branch. That's hard because you have all these superficial temporal vessels that usually are deep to it, but there are - sometimes, there’s branches above it, so the best thing to do is instead of - I try to - tend to follow the superior most aspect. If this is your nerve, instead of dissecting this way - it's going up - I try to stay on that side of it - that way, so I can see it going superiorly, okay? You can open all that up. Let’s see. I think the branch is going this way. You can see your superficial temporal vessels there, and then you would follow it the other way also. So I’m going to take that. So there's the lower division there. You can see it right there. See, I'm just taking everything. So the other thing to remember is - and this is important - is that the lower division - particularly the marginal mandibular nerve - its relationship to the retromandibular vein and the posterior facial vein; it's always superficial to it, okay? So you got to look for that, and that nerve will go over the top, and you can see - I think this is - this is a vein here, and the nerves are going deep to this. You got to actually follow those nerves. Those ves - those nerves and then divide these vessels above it. Okay? Let me just take it here. Hope I don't cut it here. Let’s see. So there's - this is probably platysma branch going down. This is probably the marginal branch going up, okay?
CHAPTER 7
So then when you get to this point, I’m just going to do this for expediency's sake. I'm going to take all of these. There’s a big vessel there. I'm just going to go ahead and take this, okay? Because I want to get to the deep lobe. The dissection of the peripheral branches is pretty straightforward. So now - if you hold that out - the deep lobe anatomy is important, and you know, as I told Helen the other day, is whenever you're doing a parotid, you need to be prepared to do a total, okay? Depending on the pathology. So, the first thing you do is you basically mobilize - mobilize the nerve, okay? Off. Just mobilize the nerve off all the soft tissue. Then, you've got to control the superficial temporal vessels up here. You got to find the terminal branch of external carotid. It's best to find it low. I think it comes between - it's right here. Okay now, the point here is that the terminal branch of external carotid and the posterior facial - the retromandibular vein, again, go deep to the nerve. So, if you're doing a deep low parotid tumor or a parapharyngeal space tumor, you don't have to identify the facial nerve if you’re deep to those structures, okay? It's safe, and that’s one way to look at it - superficial versus deep lobe - because deep lobe tumors are going to be deep to those vessels. So you can dissect it out. You just got to follow all of the - and just detach all of the parotid from the posterior border of the mandible, here, and... There's the stylomandibular ligament and all of that stuff, but your deep - your deep part of your resection is your styloid, which is here, okay? And as you come across the front, the vessels you often forget about are the internal maxillary artery and vein, so you've got to find those, control them, take the artery here above and below, take the IMA, and then you can free up all the deep lobe off the styloid until you get to the parapharyngeal fat - and you just slide it under your nerves, okay?