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Head and Neck Imaging
April 2003

Recurrent Pleomorphic Adenoma of the Parotid Gland in Pediatric and Adult Patients: Value of Multiple Lesions as a Diagnostic Indicator

Abstract

OBJECTIVE. Recurrent pleomorphic adenoma of the parotid gland is a significant problem. Rates have been as high as 40% in some series of patients who have undergone surgery for the primary lesion. In the imaging literature, anecdotal case reports show multiple lesions in recurrent pleomorphic adenoma. Our aim was to analyze the imaging of a series of patients to determine the reliability of multiple lesions as a tool in diagnosing recurrent disease.
MATERIALS AND METHODS. Medical records of the patients with recurrent pleomorphic adenoma of the parotid gland referred to our institution were retrospectively reviewed. Before the second surgery, MR imaging had been performed in 15 patients. We retrospectively reevaluated and scored the MR imaging studies with particular attention paid to the location and number of the lesions and the remaining parotid gland tissue.
RESULTS. On the basis of imaging findings, eight patients underwent enucleation, superficial parotidectomy had been performed in four patients, and three patients underwent total parotidectomy. For our group, the lesions were multiple in 73.3% of patients.
CONCLUSION. To our knowledge, we present the first large series of imaging studies in recurrent pleomorphic adenoma of the parotid gland. Our findings show that recurrent pleomorphic adenomas are most likely to be multiple. Such multiplicity of lesions is a reliable diagnostic indicator of recurrent disease.

Introduction

Pleomorphic adenoma, also known as benign mixed tumor, is the most common tumor of the salivary glands [1]. Pleomorphic adenomas comprise approximately 70% of all neoplasms of the parotid gland [1, 2]. The tumor is almost always solitary. Multiple or bilateral pleomorphic adenomas are rare [3, 4, 5]. After surgical resection, up to 43% of patients are at risk for recurrence, even as long as 45 years after the initial surgery. One factor that contributes to recurrence is a unique histologic characteristic of pleomorphic adenomas. These tumors lack a true capsule and have small protrusions, pseudopodia, that extend beyond the central tumor mass [6]. In recurrent cases, imaging findings may be equivocal because nonspecific anatomic changes in postsurgical sites make it difficult to diagnose with certainty the presence of new tumor. This difficulty is of great importance to the clinician if fine-needle aspiration biopsies are needed or for counseling patients about the risk to the facial nerve in revision surgery.
Despite the prevalence of recurrent pleomorphic adenomas, to our knowledge, large studies of imaging findings have not been reported. We are aware of imaging case reports in the English literature [7, 8]. To more clearly define the value of imaging in recurrent pleomorphic adenomas, we retrospectively examined a group of patients referred to a large university hospital. To our knowledge, we present the first large series of the imaging appearance of recurrent pleomorphic adenoma of the parotid gland and describe a potentially novel sign, multiple lesions, as diagnostic for recurrent disease.

Materials and Methods

We retrospectively analyzed the records of patients treated for recurrent pleomorphic adenoma of the parotid gland from 1985 through 2000. MR imaging of the parotid gland was available in 15 patients who later underwent second surgeries. Two head and neck radiologists reviewed the studies to determine the number of tumor foci and whether the recurrent lesion was solitary or multiple. Also, these radiologists noted any residual parotid gland tissue on the affected site. Because all patients had primary surgeries performed elsewhere, operative reports were not always available. Thus, MR imaging evidence of residual tissue and notes from the second surgery at the University of California at Los Angeles were used to clarify the true extent of the original surgery. If no parotid gland tissue was visible on the operated side, it was assumed that a total parotidectomy was performed. If only deep lobe tissue was visible, it was assumed that a superficial parotidectomy was the initial surgery. If parotid gland tissue in the superficial lobe was visible, then it was presumed that an enucleation or incomplete resection was performed. The data were analyzed to see if there was an association between multiple lesions (or number of lesions) and age at the time of the initial resection, age at recurrence, time to recurrence, and type of original surgery or sex.

Results

The patient cohort included nine females and six males who were 13–57 years old at first surgery (mean age, 29.1 years). The time between primary surgery and recurrence was 2–23 years (mean, 16.3 years). Three patients subsequently developed carcinoma ex pleomorphic adenoma. MR imaging was performed before the second surgery, at which a diagnosis of recurrent pleomorphic adenoma was established. On the basis of the imaging studies, eight patients underwent enucleation, and two patients underwent superficial parotidectomy. Total parotidectomy was the primary surgical procedure for five patients. On the imaging studies, 11 (73.3%) of the 15 patients had multiple lesions. Of these, one patient had five, two patients had four, and six patients had three lesions. Two patients had two lesions at the site of the primary surgery (Figs. 1A, 1B and 2). The demographics, type of original surgery, time to recurrence, and number and distribution of recurrent lesions are presented in Table 1.
Fig. 1A. 39-year-old woman who underwent enucleation of left parotid gland mass 19 years previously and who presented with fullness in her throat. P = normal parotid gland on right. Unenhanced T1-weighted axial MR image shows multiple solid masses (arrows) in left parapharyngeal space causing narrowing of airway (arrowhead).
Fig. 1B. 39-year-old woman who underwent enucleation of left parotid gland mass 19 years previously and who presented with fullness in her throat. P = normal parotid gland on right. T2-weighted MR image shows lesions (arrows) to be hyperintense. Arrowhead points to narrowed airway.
Fig. 2. 41-year-old woman who underwent left superficial parotidectomy 15 years previously and who presented with nodules near left earlobe. Unenhanced T1-weighted axial MR image shows several round, low-intensity lesions (arrows) at parotidectomy bed. P = normal parotid gland on right.
TABLE 1 Details of 15 Patients in Study Group
Patient No.SexAge at Primary Surgery (yr)Age at Recurrence (yr)Time to Recurrence (yr)No. of Lesions on MR ImagingType of Primary SurgerySite of Recurrence
1M4274324EnucleationParotid space
2M242955SuperficialParotid space
3F424421TotalParotidectomy bed
4F1636201EnucleationParotid space
5F2641153SuperficialParotid space
6F2039193EnucleationBuccal region along the Stensen's duct
7F404771TotalParotidectomy bed
8M4568232EnucleationParotid space
9F1732154EnucleationParotid space
10F263593EnucleationParotid space
11F293123EnucleationParotid space, parapharyngeal space
12M1343303TotalParotidectomy bed
13F576372EnucleationParotid space
14M1953341TotalParotidectomy bed
15
M
21
46
25
3
Total
Parotidectomy bed
Statistical analysis was performed using the Student's t and chi-square tests at the 5% significance level. Additionally, confidence interval (CI) estimates were obtained using the techniques of Blyth and Still [9]. The singularity of lesions occurred in the sample with an estimated proportion of 0.267 (95% CI, 0.097–0.551). This statistic shows that for the patients in our study group, it was more likely (73.3%) for them to have multiple lesions than to have single lesions. The Student's t test showed that women had their recurrences significantly earlier than men, 10.6 years compared with 24.8 years (p = 0.007), respectively. Also, of the eight patients who had undergone enucleation as the primary surgery, seven had multiple lesions.

Discussion

Pleomorphic adenoma is the most common tumor of the salivary glands and is most commonly located in the parotid gland [1, 2]. Several factors have been associated with recurrence. First, a strong relationship exists between the surgical technique and recurrence rate [2]. Enucleation yielded the highest recurrence rates, whereas superficial or total parotidectomy was associated with low recurrence rates [10]. Overall, the recurrence rate was estimated to be between 8% and 45% after enucleation, between 2% and 5% after superficial parotidectomy, and less than 0.4% after total parotidectomy [1, 2, 4, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23]. Second, tumor spillage during surgery, due to capsular rupture, was also an important factor for determining recurrence [6, 14, 23].
Pleomorphic adenomas do not have true capsules. Rather, they have pseudocapsules with small protrusions, pseudopodia, extending into the surrounding normal parotid gland tissue [24]. In 1998, Henriksson et al. [25] showed an increased incidence of pseudopodia in primary pleomorphic adenomas that subsequently recurred. Presumably, during enucleation, as the main tumor mass is being resected, pseudopodia are left in the gland, giving rise to multiple nodular recurrences (Fig. 3A, 3B, 3C, 3D). This presumption would explain the increased incidence of recurrence with removal of tumor alone without a “cuff” of normal surrounding gland.
Fig. 3A. Proposed mechanism for multiple lesions in recurrent pleomorphic adenomas of parotid gland. Drawing shows tumor as round mass with protrusions into surrounding tissue.
Fig. 3B. Proposed mechanism for multiple lesions in recurrent pleomorphic adenomas of parotid gland. Drawings show that as enucleation is performed (B), protrusions are left behind (C).
Fig. 3C. Proposed mechanism for multiple lesions in recurrent pleomorphic adenomas of parotid gland. Drawings show that as enucleation is performed (B), protrusions are left behind (C).
Fig. 3D. Proposed mechanism for multiple lesions in recurrent pleomorphic adenomas of parotid gland. Drawing shows that with time, these foci of tissue become larger and more confluent.
Radiotherapy after surgery has been used for incompletely resected tumors and after surgery complicated with tumor spillage [26]. However, the use of radiotherapy for a benign neoplasm is controversial because of the increased risk for malignant transformation. Moreover, such therapy can result in long-term morbidity, such as hearing loss [27, 28, 29, 30, 31].
Recurrent disease usually occurs late; therefore, some authors claim that follow-ups in less than 10 years are meaningless when reporting a lack of recurrence [6]. It is important to control disease at the outset because of the high rate of recurrent tumors and low, but significant, risk of malignant transformation [3, 7]. When evident, recurrent tumors may require repeated surgery, potentially increasing the risks for facial nerve injury and disfiguring outcome. At the time of the second surgery, approximately half the recurrences are multiple (ranging from 46% to 67%) [6, 32, 33].
Surprisingly, given its prevalence, we have found few reports in the literature about the imaging characteristics of recurrent pleomorphic adenoma of the parotid gland. Som et al. [7] described the imaging findings in one patient with recurrent pleomorphic adenoma of the parotid gland in whom the tumors were multiple. Yasumoto et al. [8] described imaging characteristics of four recurrent pleomorphic adenomas of the parotid gland. Three of these patients had multiple lesions. One head and neck imaging textbook [34] asserts that multiplicity is a frequent imaging characteristic for recurrent pleomorphic adenoma, yet the only cited literature is a single case report [7].
The signal and enhancement characteristics of the recurrent pleomorphic adenomas of the parotid gland are nonspecific. The lesions are round and of low intensity on T1-weighted images and of high intensity on T2-weighted MR images. With contrast administration, the lesions show mild enhancement.
The demographics of our series resemble those of the surgical and pathologic literature. Our female-to-male ratio of 1.5:1 is comparable to the ratios found in the literature [6, 32, 33, 35]. The mean age at the time of recurrence was 45.4 years in our series, which compares well with other figures, ranging from 32 to 44 years [6, 32, 33, 35]. The mean time between initial surgery and recurrence was 16.3 years in our group. This is higher than figures given in the surgical literature [32, 33, 35]. The longest mean time to recurrence, reported by Laskawi et al. [35], was approximately 12 years. The largest number of patients with multiple lesions, 11 (73.3%) of 15 patients, was found in our series. Multiple lesions tended to be grouped spatially. The rate of multiple lesions in our series (73.3%) slightly exceeded the rates of 55% and 67% found in the surgical literature [6, 32].
Most parotid gland masses are solitary. The normal or abnormally enlarged intraparotid lymph nodes can be seen as multiple masses, but they are rarely grouped spatially. Multiple lymphoepithelial cysts can be seen in HIV-positive patients, but these cysts are often bilateral, and their cystic imaging appearance is characteristic [34]. Parotid gland abscesses can be multiple, but the distinct clinical setting rarely causes confusion. Warthin's tumor, usually a cystic mass, is the most common multifocal parotid gland neoplasm. On imaging, Warthin's tumor usually appears as a single cystic mass [34]. Approximately 10% of Warthin's tumors are bilateral [36].
Therefore, we conclude that when multiple masses are seen in the parotid gland or in the region of the parotid gland, recurrent pleomorphic adenoma is likely. Because the time to recurrence may be as long as 45 years [6], a history of a parotid gland tumor resection can be blurred. The radiologist should be aware of this characteristic appearance and raise the possibility of recurrent pleomorphic adenoma even without an adequate history for the patient.

Footnote

Address correspondence to K. Koral.

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Information & Authors

Information

Published In

American Journal of Roentgenology
Pages: 1171 - 1174
PubMed: 12646477

History

Submitted: May 7, 2002
Accepted: August 29, 2002

Authors

Affiliations

Korgün Koral
Department of Radiological Sciences, Center for the Health Sciences, UCLA School of Medicine, 650 Charles E. Young Dr., S., Los Angeles, CA 90095.
Present address: Department of Radiology, University of Texas Southwestern Medical Center at Dallas and Children's Medical Center of Dallas, 1935 Motor St., Dallas, TX 75235.
James Sayre
Department of Radiological Sciences, Center for the Health Sciences, UCLA School of Medicine, 650 Charles E. Young Dr., S., Los Angeles, CA 90095.
Sunita Bhuta
Department of Surgical Pathology and Laboratory Medicine, Center for the Health Sciences, UCLA School of Medicine, Los Angeles, CA 90095.
Elliot Abemayor
Department of Surgery, Division of Head and Neck Surgery, Center for the Health Sciences, UCLA School of Medicine, Los Angeles, CA 90095.
Robert Lufkin
Department of Radiological Sciences, Center for the Health Sciences, UCLA School of Medicine, 650 Charles E. Young Dr., S., Los Angeles, CA 90095.

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