Introduction
Extracapsular dissection (ECD) challenges the need to remove most of the parotid gland to prevent tumor recurrence. The dissection takes place within the parotid tissue, 2–3 mm peripheral to the palpable and visible tumor edge. In traditional parotidectomy, tumor removal with wide surgical margin (>5 mm) is not achieved in most cases because the facial nerve runs in close proximity to the tumor capsule. A partial ECD is undertaken in most traditional operations. There is ample evidence now to show that ECD is a safe technique with low morbidity. A second difference is that the facial nerve does not dictate the surgical approach. At the start of the traditional procedure the facial nerve trunk is identified and the nerve dissected from the parotid gland. Only then is attention turned to the tumor. In ECD, the tumor is central to the dissection. Careful technique and continuous facial nerve monitoring mean the surgeon can move through the gland with confidence.
History of Parotid Surgery
In the 1930s, McFarland became aware of the high recurrence rate (~40%) of parotid tumors. Surgical provision of care was different at that time. There was no pathologic classification of benign parotid tumors and no subspecialization. The operators were true “general surgeons” with their practice aimed at gross disease and ranging across the body. By comparison, an apparent cyst or benign developmental lump in the parotid was a modest challenge. Surgery was under local anesthesia and the common approach was an incision made directly over the lump. Poor access meant that spillage was common. By the 1940s there was a move by prominent surgeons, notably Janeway in Canada, Hamilton Baily in London, and Redon of Paris, to introduce a new anatomic approach to parotid surgery, namely separating the parotid gland into two halves by dissecting along the facial nerve. This coincided with an improvement in results and a proposed explanation by Patey and Thackray placing the blame for recurrence on the biology of the tumor (dehiscent capsule) and not the operative technique. Nicholson, who was practicing ECD through the 1930s and 1940s, held that the wide surgical exposure dictated by this new surgical approach was the true explanation for the decrease in recurrent disease. He continued with ECD, as did Gleave, and their results confirmed that careful dissection around the periphery of the tumor was safe. The results of ECD have since been confirmed in meta-analysis.
Patient Selection
An ECD is defined as removal of a tumor with a cuff of healthy tissue without routine elective exposure of the main trunk of the facial nerve. This surgical modality is ideally suited to cases of a solitary mobile lesion, which, on both clinical examination and imaging, is suggestive of a benign tumor located lateral to the sagittal plane of the facial nerve. But with experience, it has much wider application and can be adapted to almost all benign tumors in the parotid gland (see Advanced technique, below ). Interestingly, the one anatomic area where there is no debate on surgical approach, and where the ECD approach is mandatory, is the parapharyngeal space. Here, finger dissection is the norm. Margins are tight, but the results are surprisingly good.
Paradoxically it is small tumors (<2 cm) that are not appropriate for ECD. Small lumps are difficult to palpate and image discerningly. The problem is that low-grade cancers can masquerade as benign lumps not appropriate for ECD technique. But if the tumor has every appearance of being benign, experience shows that surprisingly, ECD is not associated with an adverse outcome. This does not mean ECD is advocated in such a situation but if a low-grade malignant tumor is treated by ECD, then a course of adjuvant therapy gives an optimum outcome. The ideal tumor on which to commence ECD is 2–4 cm in diameter, well-defined, mobile, and situated in the tail or superficial part of the parotid. The majority of benign parotid tumors are amenable to ECD.
Investigation
The primary evaluation is clinical and ultrasound (US). If a complex mass extends deep to the mandible, or those tightly wedged between the mandible and mastoid or lying in the parapharyngeal space, an MRI is indicated.
Due to the high rate of false-negative results, fine needle aspiration cytology (FNAC) with cytologic examination has limitation in the assessment of salivary gland tumors. Core needle biopsy, performed under local anesthesia, preserves tissue architecture and provides a better opportunity to distinguish benign from malignant disease. An added advantage is the availability of a battery of immunohistochemical markers.
ECD Technique
The standard approach is suitable for mobile tumors lying over the mandible or tail of the parotid ideally superficial to the facial nerve ( ). A roll is placed under the ipsilateral shoulder. Continuous facial nerve monitoring is applied and a preauricular incision (with a retrotragal extension) is drawn so that a skin flap is raised just above the parotid fascia (superficial musculoaponeurotic system [SMAS] flap) to expose the area around the tumor ( Fig. 37.1 ). The position of the tumor dictates the size and position of the incision. Commence with large incisions and, later with experience, gradually reduce their size. Once the tumor is exposed, a cruciate incision line is marked over the tumor extending at least 1 cm past the periphery of the tumor ( Fig. 37.2 ). This extension is important to the successful execution of the technique. Four small artery clips are attached to the fascia at the intersection of the cruciate lines. They allow traction to be applied to the parotid tissue, which is a unique feature of this technique and helps identify loose tissue planes around the tumor that facilitate ECD. An incision is made through the fascia after tenting it up with the artery clips ( Fig. 37.3 ). The incision must extend at least 1 cm past the periphery of the tumor. The four quadrants, defined by the cruciate incision, are carefully dissected free from the tumor, aided by traction through the artery clips. Traction on the artery clips pulls the compressed parotid tissue away from the periphery of the lump and frequently provides clear planes of dissection. Progress is by blunt dissection; only small pinches of tissue are undermined by the point of the scissors and nothing should be cut or cauterized without being able to see through the tissue. Move from side to side of the tumor when progress gets slow at any one position. If the facial nerve becomes apparent, dissect it aside. If it courses over the tumor, give the nerve enough freedom to be slipped off the surface of the tumor, then continue the blunt dissection. Unlike superficial parotidectomy, the tumor is exposed and vulnerable ( Fig. 37.4 ). This is compounded by assistants trying help progress the dissection with a retractor that incurs the risk of perforation. Consequently, the rule is that only the surgeon handles the tumor. The assistant provides traction only on the normal salivary tissue. Hemostasis should be meticulous. Once the tumor is removed, the petals of parotid tissue are re-approximated along the cruciate incision lines, re-establishing the integrity of the parotid fascia and the barrier to Frey syndrome ( Fig. 37.5 ). The use of a suction drain is optional and depends on the extent of dissection, but a mastoid pressure dressing is always applied and worn for 48–72 h, as advised by the originators of the technique, Gleave and Nicholson. This reduces the risk of sialoceles or salivary fistulas ( Fig. 37.6 ).
