A Rare Case of Carcinoma Ex-pleomorphic Adenoma

Abstract

Pleomorphic adenoma is the most common benign salivary tumor involving the parotid gland. However, malignant transformation to carcinoma expleomorphic adenoma (CXPA) is an exceedingly rare occurrence. Malignant patterns reported with pleomorphic adenoma include CXPA, metastasizing pleomorphic adenoma, and carcinosarcoma. Firm mass in the parotid gland is the most common presentation of CXPA. Imaging appearances of CXPA are variable, and the proportion of carcinoma and adenoma components determine the appearance of the lesion on gross pathology. Histopathology remains the gold standard investigation for the confirmation of diagnosis. The treatment of CXPA includes ablative surgical procedure followed by reconstructive surgery. This case report describes the imaging appearances of a rare case of CXPA in a 19-year-old male.

INTRODUCTION

Pleomorphic adenoma is the most common benign tumor arising commonly from the parotid gland. However, pleomorphic adenoma has also been reported from other major salivary glands. Malignant transformation of pleomorphic adenoma is exceedingly rare. The factors associated with malignant transformation include a larger tumor size, longer duration, rapid growth, advanced patient age, tumor recurrence after surgery, and administration of radiotherapy. Carcinoma expleomorphic adenoma (CXPA) occurs secondary to malignant transformation of a primary benign pleomorphic adenoma. The appearances of CXPA are variable, and the proportion of carcinoma and adenoma components of the tumor determine the appearance of the lesion on gross pathology. Preoperative imaging diagnosis is often difficult and poses a diagnostic challenge to pathologists as well.

CASE REPORT

A 19-year-old male presented to the department of general surgery with progressive increase in the size of the left parotid gland for 6 months. Clinical examination revealed a firm, nontender mass in the left parotid with no signs of cranial nerve VII paralysis. Magnetic resonance imaging (MRI) revealed a well-circumscribed mass measuring 19 mm × 19 mm × 18 mm in the left parotid gland. The mass lesion showed heterogeneous signal intensity with the lateral most component appearing isointense; the intermediate component appearing predominantly hypointense; and the medial most component appearing predominantly hyperintense on T2-weighted images. T1+ contrast images showed heterogeneous enhancement [Figure 1a and b]. The lateral most component of the lesion demonstrated mild restriction on diffusion-weighted images and apparent diffusion coefficient mapping. Computed tomography (CT) scan revealed dense central calcification within the mass lesion [Figure 2]. The patient underwent surgical resection of the left parotid gland. On histopathological examination, the lateral component of the resected specimen was proven to be carcinoma; the intermediate component was proven to be pleomorphic adenoma with distinct fibrosis; and the medial component was proven to be pleomorphic adenoma with a blatant chondroid matrix [Figure 3]. A diagnosis of CXPA was made based on the histopathology findings. Contrast-enhanced CT at 6 months’ follow-up revealed no features of recurrence.

Figure 1.

(a) Coronal T2 magnetic resonance image demonstrating a well-demarcated mass with heterogeneous intensity in the left parotid gland. (b) Coronal T1+ contrast magnetic resonance image demonstrating contrast enhancement of the medial component of the left parotid lesion

Figure 2.

Axial computed tomography image revealing dense central calcification in the left parotid lesion

Figure 3.

Histopathology image demonstrating areas of low-grade pleomorphic adenoma similar to that seen in the salivary gland (H and E, ×40)

DISCUSSION

Pleomorphic adenoma is a benign mixed tumor with varying proportions of mesenchymal, epithelial, myoepithelial components on histopathology. Pleomorphic adenoma commonly occurs in females with approximately 80% involving the parotid gland.[1] Malignant transformation to CXPA has been reported in 6% cases.[2] CXPA is a rare and aggressive malignant lesion with the high rate of regional metastases and mortality.[3] Relatively small-sized mixed component which can be often missed and difficulty in classifying the malignant component pose as challenges in making a precise diagnosis of CXPA.

Sudden rapid growth encountered in an otherwise slow-growing pleomorphic adenoma of the parotid gland should raise the suspicion of CXPA. CXPA constitutes the majority of misdiagnosed malignant tumors of major salivary glands and should be included in the differential diagnosis of a metastatic mixed tumor or a high grade adenocarcinoma that is difficult to classify.[4]

Superficial parotidectomy for localized tumors in the superficial lobe and complete parotidectomy for aggressive tumors involving the deep lobe are often undertaken as management options for CXPA. Reconstructive procedures following surgery may or may not be required.[5]

MRI findings of malignant tumors involving major salivary glands include heterogeneous signal intensity of the lesion appearing predominantly hypointense on T2-weighted image sequences, irregular margins of the lesion, and tumor infiltration into surrounding tissues. Benign lesions such as pleomorphic adenoma are typically well-circumscribed with regular margins, appearing hypo-to-isointense signal intensity on T1-weighted sequences and iso-to-hyperintense signal intensity on T2-weighted sequences.

CONCLUSION

Pleomorphic adenoma constitutes the most common benign salivary gland tumor. Malignant transformation of pleomorphic adenoma to CXPA is an exceedingly rare occurrence. In conclusion, MRI findings of CXPA are nonspecific pertaining to the variable proportion of carcinoma and adenoma components of the tumor. CXPA presents a diagnostic dilemma to radiologists and pathologists; hence, awareness of the entity is important for better patient management.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.