Pleomorphic adenoma (benign mixed tumor) is the most common tumor of salivary glands, accounting for 60-70% of all salivary gland neoplasms. It most frequently arises in the superficial lobe of the parotid gland (80%). Histologically, it has a mixed composition of epithelial and myoepithelial cells with chondroid, myxoid, and fibrous stromal components. The tumor is well-encapsulated but the capsule may be penetrated by pseudopod extensions, making simple enucleation inadequate and superficial parotidectomy the preferred treatment. In long-standing pleomorphic adenomas, there is a 5-25% risk of malignant transformation (carcinoma ex-pleomorphic adenoma), which increases with tumor duration. Clinically, it presents as a slowly growing, painless, mobile mass. It is slightly more common in women and is typically diagnosed between 30-60 years of age.
Age Range
30-60
Peak Age
45
Gender
Female predominant
Prevalence
Common
The characteristic imaging findings of pleomorphic adenoma are rooted in the heterogeneous histological composition of the tumor. The varying proportions of epithelial, myoepithelial, chondroid (cartilaginous), myxoid (mucinous), and fibrous stromal components result in variable signal characteristics on MRI. The high water content of the myxoid/chondroid matrix produces marked hyperintensity on T2-weighted sequences — this finding is nearly pathognomonic and is the most valuable criterion for distinguishing pleomorphic adenoma from other parotid tumors. The well-developed fibrous capsule manifests as smooth and sharp margins on imaging; however, it should be recognized that the capsule may be focally incomplete or penetrated by tumor pseudopods histologically. Enhancement occurs in solid and more cellular areas while remaining minimal in myxoid areas, explaining the heterogeneous enhancement pattern. As tumor size increases, internal hemorrhage, cystic degeneration, or calcification may develop, further adding to the heterogeneous imaging appearance. In long-standing tumors, malignant transformation may manifest with additional imaging findings such as irregular margins, necrosis, and invasion of surrounding structures.
Due to the high free water content of myxoid and chondroid stromal components, marked hyperintensity approaching CSF signal is seen on T2-weighted MRI. This finding clearly distinguishes from other parotid tumors (Warthin tumor shows intermediate-low T2, malignant tumors show intermediate T2) and is nearly pathognomonic for pleomorphic adenoma. T2 hyperintensity becomes more pronounced as the proportion of myxoid component increases.
Marked hyperintensity on T2-weighted sequences is the most characteristic MRI finding of pleomorphic adenoma. The high free water content of myxoid and chondroid stromal components prolongs T2 relaxation time, producing bright signal. This finding is especially prominent in myxoid-dominant tumors and may approach CSF signal intensity. In cellular-dominant pleomorphic adenomas, T2 hyperintensity may be less pronounced; this variant can mimic malignancy. In heterogeneous tumors, myxoid areas appear bright while fibrous areas show lower signal, creating the characteristic mosaic pattern.
Report Sentence
A well-defined lobulated mass in the parotid gland demonstrating marked hyperintense signal on T2-weighted sequences is identified, consistent with a myxoid/chondroid component dominant pleomorphic adenoma.
On T1-weighted sequences, pleomorphic adenoma typically shows isointense or mildly hypointense signal relative to muscle. Myxoid areas appear hypointense due to high water content, while cellular/fibrous areas appear isointense. Focal T1 hyperintense foci may be seen if internal hemorrhage is present. The capsule may be visible as a thin hypointense rim on T1. Cystic degeneration areas with high protein content may show mild T1 hyperintensity. Post-gadolinium contrast-enhanced T1 sequences show heterogeneous enhancement; solid and cellular areas enhance prominently while myxoid areas show no enhancement.
Report Sentence
The lesion demonstrates isointense to mildly hypointense signal relative to muscle on T1-weighted sequences, with heterogeneous enhancement on post-contrast series.
On diffusion-weighted imaging, pleomorphic adenoma typically shows no true diffusion restriction; ADC values are high (typically >1.5-2.0 × 10⁻³ mm²/s). The myxoid matrix allows free water diffusion, resulting in hyperintensity on ADC maps. This feature is extremely valuable in distinguishing from malignant tumors that show diffusion restriction (ADC typically <1.0-1.2 × 10⁻³ mm²/s). However, in cellular-dominant pleomorphic adenomas, ADC values may be relatively lower and can mimic malignancy. T2 shine-through effect may create hyperintensity on DWI at high b-values; therefore, correlation with ADC maps is always necessary.
Report Sentence
The lesion does not demonstrate true diffusion restriction on diffusion-weighted sequences, with high signal on ADC maps; this finding supports a benign pathology, particularly pleomorphic adenoma.
On contrast-enhanced CT, pleomorphic adenoma appears as a well-defined, homogeneously or heterogeneously enhancing solid mass in the parotid gland. Small tumors generally enhance homogeneously, while larger tumors show heterogeneous enhancement due to myxoid degeneration and cystic areas. On non-contrast CT, the tumor is generally of soft tissue density (40-70 HU). Calcifications, although rare (2-5%), may be seen in pleomorphic adenoma and can be dystrophic or flocculent in pattern. Tumor margins are generally sharp and smooth; irregular margins should raise suspicion for malignant transformation. CT is useful in evaluating bone invasion and demonstrating deep lobe extension of the tumor, but soft tissue contrast is inferior to MRI.
Report Sentence
A well-defined soft tissue mass with lobulated contours and heterogeneous enhancement on post-contrast series is identified in the parotid gland; pleomorphic adenoma should be the primary consideration.
On B-mode ultrasonography, pleomorphic adenoma typically appears as a well-defined, lobulated, homogeneous hypoechoic solid mass. Posterior acoustic enhancement may be observed behind the posterior wall of the tumor — this finding results from the myxoid matrix conducting sound waves well and may be confused with cystic lesions. In larger tumors, internal echo heterogeneity, cystic areas, and calcifications may be seen. The capsule may be identified as a thin echogenic rim. The tumor is clearly separated from surrounding tissues and shows minimal deformation with compression (reflecting its firm consistency). US plays an important role in the initial evaluation of pleomorphic adenoma, fine-needle aspiration biopsy (FNAB) guidance, and postoperative follow-up.
Report Sentence
A well-defined, lobulated, homogeneous hypoechoic solid mass with posterior acoustic enhancement is identified in the parotid gland; findings are primarily consistent with pleomorphic adenoma.
On Doppler ultrasonography, pleomorphic adenoma typically shows minimal or scant internal vascularity. Peripheral vascularity (feeding artery) may be seen but internal flow is generally low. This low vascularity pattern reflects the avascular nature of the myxoid matrix and is a supportive finding in differentiating from malignant tumors. More internal vascularity may be observed in cellular-dominant variants or large tumors. Spectral Doppler typically shows low flow velocities and high resistive index. Contrast-enhanced ultrasonography (CEUS) demonstrates homogeneity and low enhancement.
Report Sentence
Color Doppler examination reveals minimal internal vascularity within the lesion with identification of a peripheral feeding vessel; the low vascularity pattern is consistent with a benign salivary gland tumor.
On Tc-99m pertechnetate scintigraphy, pleomorphic adenoma does not show radiotracer uptake (cold nodule). This finding is critical in distinguishing pleomorphic adenoma from Warthin tumor; Warthin tumor shows prominent pertechnetate uptake (hot nodule) due to mitochondrial activity of oncocytic cells. In pleomorphic adenoma, there is no or minimal functional salivary gland epithelium, therefore pertechnetate (an iodine analogue actively taken up by salivary glands) is not accumulated. This negative finding is not specific for diagnosis alone as other malignant and benign tumors may also appear as cold nodules.
Report Sentence
On Tc-99m pertechnetate scintigraphy, the parotid gland mass does not demonstrate radiotracer uptake (cold nodule); this finding is supportive in excluding Warthin tumor.
Criteria
Predominance of myxoid/chondroid matrix in the stromal component (80% and above). Most common histological variant.
Distinct Features
Very marked hyperintensity on T2-weighted MRI (CSF-like), homogeneous signal, high ADC values (>2.0 × 10⁻³ mm²/s), minimal enhancement, posterior acoustic enhancement prominent on US. Lower risk of malignant transformation.
Criteria
Predominance of epithelial and myoepithelial cells over stromal matrix. Less common variant.
Distinct Features
Less pronounced T2 hyperintensity (intermediate signal), lower ADC values (1.0-1.5 × 10⁻³ mm²/s — may mimic malignancy), more prominent enhancement, posterior acoustic enhancement decreased or absent on US. Risk of malignant transformation may be higher than myxoid variant.
Criteria
Malignant transformation in a long-standing pleomorphic adenoma. Tumor duration >15 years, sudden rapid growth, pain, facial nerve paralysis are diagnostic clues.
Distinct Features
Irregular margins, capsule destruction, invasion of surrounding structures, necrosis, previously homogeneous mass becoming heterogeneous, diffusion restriction, low ADC (<1.0 × 10⁻³ mm²/s), aggressive enhancement pattern. 'Tumor within tumor' appearance may be diagnostic.
Criteria
Pleomorphic adenoma originating from palatal, labial, buccal, or other minor salivary glands. Extra-parotid location, generally smaller in size.
Distinct Features
Most common in the hard palate; presents as a submucosal, well-defined mass. Bone erosion may rarely be seen. T2 hyperintense, enhancing mass on MRI. Capsule may be thinner or absent compared to parotid location, therefore recurrence risk is higher with inadequate resection.
Distinguishing Feature
Warthin tumor shows intermediate-low T2 signal (unlike the marked hyperintensity of pleomorphic adenoma), is located in the parotid tail, may be bilateral/multifocal, cystic components are more prominent, and shows Tc-99m pertechnetate uptake (hot nodule).
Distinguishing Feature
Low-grade mucoepidermoid carcinoma is well-defined and may mimic pleomorphic adenoma; however, T2 hyperintensity is less pronounced, T1 hyperintensity in cystic components (mucinous content) may be seen, and ADC values are lower. High-grade variant shows irregular margins and aggressive features.
Distinguishing Feature
Schwannoma may also be T2 hyperintense but may show target sign (central hypointensity, peripheral hyperintensity), has fusiform morphology, and follows the course of the facial nerve. Unlike pleomorphic adenoma, it appears as an elongated mass centered on the nerve.
Distinguishing Feature
Adenoid cystic carcinoma has irregular margins, perineural spread (enhancement along nerve — extension to cranial foramina). Shows intermediate T2 signal, diffusion restriction, low ADC. Perineural spread is the hallmark finding of adenoid cystic carcinoma and is not expected in pleomorphic adenoma.
Distinguishing Feature
Lymphoma typically shows homogeneous low T2 signal and marked diffusion restriction (very low ADC). Bilateral parotid involvement, cervical lymphadenopathy may accompany. MALT lymphoma development in the setting of Sjögren syndrome should be queried in history. Unlike pleomorphic adenoma, T2 hyperintensity is absent.
Urgency
routineManagement
surgicalBiopsy
NeededFollow-up
Preoperatif İİAB veya kor biyopsi ile histolojik tanı önerilir. Cerrahi tedavi: süperfisiyal parotidektomi (fasiyal sinir korunarak). Basit enükleasyon rekürrens riski nedeniyle önerilmez. Postoperatif yıllık klinik ve US takip minimum 5 yıl.Pleomorphic adenoma is a benign tumor but requires surgical excision. If left untreated, it continues to grow slowly and the risk of malignant transformation increases over time (5-25%, especially in tumors >15 years old). Superficial parotidectomy is the gold standard treatment; the facial nerve must be preserved. Simple enucleation is associated with 20-45% recurrence (due to capsule pseudopods). In recurrent pleomorphic adenoma, multifocal nodules may develop and surgery is more complex. FNAB diagnostic accuracy is 90-95%. MRI is mandatory preoperatively to evaluate deep lobe extension, facial nerve relationship, and tumor size.
Superficial parotidectomy is the standard treatment. Simple enucleation is insufficient due to recurrence risk. Risk of malignant transformation (carcinoma ex-pleomorphic adenoma) in long-standing tumors is 5-25%.