22 Parotid-Benign Disease

John F. Carew

Parotidectomy for the primary treatment of tumors of the parotid gland, in general, is a satisfying surgical procedure. These tumors are usually benign, unifocal, and freely mobile. With adequate surgical excision, including dissection and preservation of the facial nerve, the recurrence rate for these tumors is < 5%.1–3 The cause of the recurrence may be related to surgical technique, tumor biology, or a combination of the two. Regardless of the cause of the recurrence, when tumors do recur, their surgical treatment can be tedious and technically challenging. In this chapter, the clinical characteristics of recurrent tumors of the parotid gland and their treatment will be discussed.

It should be noted that pleomorphic adenomas are by far the most common tumors to arise in the parotid gland.⁴ Not surprisingly, they are also the most common benign tumor to recur. For this reason, this chapter will present comment on recurrent pleomorphic adenomas of the parotid unless specified otherwise.

Factors Predisposing to Recurrence

Many factors have been linked to the recurrence of pleomorphic adenomas of the parotid gland. The first and most well-established factor is the extent of initial surgery. There are ample data to support the contention that the enucleation or limited local excision results in a high rate of recurrence. In series published in the past, where this surgical technique was used, high rates of recurrence were seen that approached 50% in some reports.^5,6 For this reason, it is now well accepted that adequate surgical excision with at least a small cuff of normal parotid tissue surrounding the tumor should be resected at the time of primary treatment. It should be noted, however, that in many cases, at least a portion of the dissection is too close to the margin of the tumor during dissection of the facial nerve. Despite this, relatively low rates of recurrence are seen.

Occasionally, however, pleomorphic adenomas of the parotid gland may recur despite adequate primary surgical treatment. Several factors have been postulated to be related to this and include tiny microscopic extensions of the tumor beyond the pseudocapsule of the tumor, multifocality of the tumor, or rupture of the capsule of the tumor during primary surgical excision. Although these factors seem intuitively obvious, retrospective reviews by Buchman et al, Henriksson et al, and Natvig and Soberg failed to consistently reveal these as strong predictors of recurrence.^7–9 These studies, however, are limited by several factors. First, most of these studies deal with a very small number of recurrent tumors, as these tumors are uncommon and rarely recur. Additionally, they relied on operative reports for determining tumor capsule rupture. Unfortunately, operative reports do not always fully reflect the events that transpire. Surgeons may be hesitant to report capsule rupture for obvious medical and legal reasons. Despite their limitations, the reviews did not show a statistically significant increase in recurrence rate when the operative report specifically stated that the tumor capsule was ruptured.^7–9 In these reviews, the rate of recurrence when tumor capsule rupture was reported ranged from 0 to 8%. In all three studies, this is not significantly different from the recurrence rate when tumor capsule rupture was not reported. Although these studies did not show a relationship between tumor capsule rupture and recurrence, there is anecdotal evidence that this may be a source of recurrence. This evidence stems from the fact that many times when pleomorphic adenomas of the parotid recur, there are multiple tumor nodules studding the operative bed. Certainly, this pattern of recurrence is highly suggestive of tumor spillage as a possible mechanism for recurrence. Immunohistochemical studies have shown a high-level expression of integrin molecules on pleomorphic adenomas.¹⁰ These cell surface receptors are involved in cell–cell and cell–extracellular matrix interactions. Their presence may in part account for cases where multiple tumors recur throughout the operative bed.

Although anecdotal evidence exists for tumor capsule rupture as an etiology for recurrence, more compelling evidence exists for microscopic extensions of tumor past the surgical margins. In one study, 57% of patients with microscopic extensions of tumor past the surgical margins had tumor recurrence.⁷ In another, however, positive surgical margins were not shown to increase the rate of recurrence.⁹ This factor, therefore, continues to remain controversial. Again, the power of these studies is limited by small sample sizes.

Finally, others have argued that this disease may be multifocal. Patient history and pathologic examples of tumor specimens rarely give evidence to support this. From the available data, it can be concluded that recurrent tumors may be the result of either inadequate initial surgery, rupture of the capsule of the tumor with contamination of the surgical bed, or microscopic extensions of the tumor beyond its capsule. Regardless of the cause, when these tumors recur, they present a surgical challenge.

Pleomorphic adenomas of the parotid gland are relatively slow-growing tumors. For this reason, recurrences often occur decades after the primary surgery. In evaluating a patient with recurrence, several important clinical factors should be considered, including the nature of the primary surgical procedure and whether it was a formal parotidectomy or an enucleation. Treatment of patients with recurrent tumors that are the result of inadequate initial surgery tends to be more successful than treatment of patients with recurrent tumors despite adequate initial surgery.11 Histologic characteristics of the primary tumor, with specific attention to the margins of the tumor, and accuracy of the histologic diagnosis should be obtained. Whenever possible, the original slides should be obtained and reviewed to confirm the accurate histologic diagnosis. Other critical clinical factors are the disease-free interval prior to recurrence and the rate of growth of the recurrent tumor. Additionally, the status of facial nerve function following the primary procedure is important to ascertain. If there was facial nerve weakness following the initial surgery, revision surgery will be more tedious and have a higher rate of facial nerve neuropraxia or permanent paralysis. Finally, it is important to determine if there was a history of radiation exposure or the use of therapeutic radiation in the past.

In addition to the clinical history, several aspects of the physical exam are critical to the evaluation of the patient with a recurrent tumor of the parotid. The pattern of recurrence, unifocal versus multifocal, is critical to surgical planning. Additionally, the relationship of the recurrent tumor to the overlying skin and scar tissue should be assessed. If the recurrence is immediately beneath the skin or the skin is tethered to the tumor, preparation should be made for sacrifice of the involved skin with appropriate reconstruction. The mobility of the tumor should also be assessed. The surgical incision should be inspected and kept in consideration when planning surgery for recurrent disease. In general, a modified Blair incision is most commonly used and can be extended superiorly and inferiorly to give adequate exposure when necessary for resection of recurrent disease. Finally, the function of all branches of the facial nerve should be critically examined.

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