Mucoepidermoid carcinoma is the most common malignant tumor of salivary glands, accounting for 30-35% of all salivary gland malignancies. It most frequently occurs in the parotid gland but can also arise in the submandibular gland and minor salivary glands (palate most common). Histologically, it consists of mucinous (mucin-secreting), epidermoid (squamous), and intermediate cell types. It is divided into three histological grades: low, intermediate, and high; prognosis largely depends on histological grade. Low-grade tumors are generally well-defined, cystic-dominant with excellent prognosis (95%+ 5-year survival). High-grade tumors are solid, aggressive, with irregular margins and can metastasize to lymph nodes and distant sites. Peak incidence occurs in middle age (40-60), with equal frequency in males and females. It is the most common salivary gland malignancy in childhood. Radiation exposure is a risk factor.
Age Range
20-70
Peak Age
45
Gender
Female predominant
Prevalence
Uncommon
The imaging findings of mucoepidermoid carcinoma are based on the histological composition and grade of the tumor. In low-grade tumors, the predominance of mucinous cells creates mucin-filled cystic cavities; these cavities appear as cystic components on imaging and may mimic benign cystic lesions. Mucinous content shows hyperintense signal on T1 due to its proteinaceous nature and hyperintense signal on T2. In high-grade tumors, the predominance of epidermoid and intermediate cells creates a solid, aggressive mass; cellular density manifests with diffusion restriction and low ADC values. Absence or invasion of the capsule is reflected as irregular margins and infiltration of surrounding structures. The vascular architecture of the tumor determines the heterogeneous enhancement pattern: low-grade tumors show mild enhancement of thin cystic walls, while high-grade tumors show aggressive neovascularization and prominent heterogeneous enhancement. MAML2 gene fusion is used as a diagnostic molecular marker.
The most distinguishing imaging feature of mucoepidermoid carcinoma is the T1 hyperintensity of mucinous fluid in cystic components. This finding is critical for distinguishing from simple cysts (T1 hypointense) and other cystic salivary gland lesions. Additionally, the cystic-solid spectrum reflecting the histological grade of the tumor (low-grade = cystic dominant, high-grade = solid dominant) can be assessed by imaging.
On T2-weighted sequences, the signal intensity of mucoepidermoid carcinoma varies greatly according to histological grade. In low-grade tumors, mucinous cystic cavities show marked T2 hyperintensity — signal approaching CSF may be seen. Thin walls and septa appear hypointense on T2. In high-grade tumors, the solid component predominates, showing intermediate T2 signal; cellular density shortens T2 time. Necrotic areas may show high T2 signal, contributing to the heterogeneous appearance. Intermediate-grade tumors fall between these two extremes and show cystic-solid mixed structure. Peritumoral edema is more prominent in high-grade tumors.
Report Sentence
A mixed mass containing high-signal cystic component and low-signal solid component on T2-weighted sequences is identified in the parotid gland; the T2 hyperintensity in the cystic component is consistent with mucinous content and mucoepidermoid carcinoma should be considered.
On T1-weighted sequences, the mucinous cystic components of mucoepidermoid carcinoma typically show hyperintense signal; this finding results from the T1-shortening effect of mucin glycoproteins. This T1 hyperintensity is a critical finding for distinguishing from simple cysts (T1 hypointense). Solid components appear isointense or mildly hypointense to muscle on T1. In high-grade tumors, since the cystic component is minimal, T1 hyperintensity may be indistinct or absent. Focal T1 hyperintense foci may be observed with internal hemorrhage. On post-contrast series, solid components and cystic walls show enhancement.
Report Sentence
The cystic components of the lesion demonstrate hyperintense signal on T1-weighted sequences; this finding is consistent with mucinous content, differs from simple cyst, and should be evaluated for mucoepidermoid carcinoma.
On diffusion-weighted imaging, the DWI/ADC characteristics of mucoepidermoid carcinoma vary according to histological grade. In low-grade tumors, mucinous fluid in cystic cavities shows high ADC values (>1.5 × 10⁻³ mm²/s). In high-grade tumors, marked diffusion restriction and low ADC values are seen in the solid component (typically <1.0 × 10⁻³ mm²/s) — this finding reflects high cellularity and increased nuclear/cytoplasmic ratio. ADC values may help in tumor grading: low ADC suggests high grade, high ADC suggests low grade. In intermediate-grade tumors, ADC values are in the intermediate range. DWI is also helpful in distinguishing the solid component from the cystic component of the tumor.
Report Sentence
Diffusion restriction and low ADC values (ADC: [value] × 10⁻³ mm²/s) are observed in the solid component of the lesion, consistent with high-grade mucoepidermoid carcinoma.
On contrast-enhanced CT, the appearance of mucoepidermoid carcinoma varies according to histological grade. Low-grade tumors appear as well-defined, cystic-dominant masses; thin smooth walls and septa show mild enhancement. The density of cystic cavities is higher than simple fluid (20-40 HU — mucinous content). High-grade tumors appear as irregular-margined, solid-dominant, heterogeneously enhancing masses; necrotic areas are seen as non-enhancing hypodense zones. Calcifications may be present rarely. Perineural spread may be seen on CT as enlarged foramen or canal. Cervical lymphadenopathy should be evaluated in high-grade tumors.
Report Sentence
A cystic-solid mixed mass is identified in the parotid gland, with cystic component density higher than simple fluid (mucinous content) and solid component demonstrating prominent enhancement on post-contrast series; mucoepidermoid carcinoma should be considered in the differential diagnosis.
On B-mode ultrasonography, mucoepidermoid carcinoma appears as a heterogeneous cystic-solid mixed mass. In low-grade tumors, the cystic component predominates; cystic cavities may be anechoic or show low-level internal echoes (mucinous content). Thin septa may be observed. In high-grade tumors, the solid component predominates, appearing as a heterogeneous hypoechoic mass; margins may be irregular. Posterior acoustic enhancement may be seen due to the cystic component. In low-grade tumors, margins are generally smooth and well-defined — may mimic a benign cystic lesion. Bilateral involvement is rare and not expected in mucoepidermoid carcinoma (distinguishing from Warthin tumor).
Report Sentence
A mass with cystic-solid mixed echopattern is identified in the parotid gland, with low-level internal echoes within cystic cavities; these findings suggestive of mucinous content should be evaluated with FNAB for mucoepidermoid carcinoma.
On FDG PET-CT, FDG uptake of mucoepidermoid carcinoma varies according to histological grade. High-grade tumors show prominent FDG uptake (SUVmax typically >5-8), reflecting high cellularity and increased glycolysis. In low-grade tumors, FDG uptake may be low or minimal (SUVmax <3) — due to cystic-dominant structure and low metabolic activity. This grade-dependent FDG uptake is helpful in differential diagnosis and prognostic assessment. PET-CT is important for staging in evaluating cervical and distant metastases. In high-grade tumors, lymph node and lung metastases may be seen as FDG-avid.
Report Sentence
On FDG PET-CT, the mass in the parotid gland demonstrates prominent FDG uptake (SUVmax: [value]); high metabolic activity is consistent with high-grade mucoepidermoid carcinoma and cervical/distant metastases should be evaluated for staging.
Criteria
Mucinous cell predominance, cystic component >50%, minimal mitosis, no or minimal atypia, no invasion. 5-year survival >95%.
Distinct Features
Well-defined, cystic-dominant mass. T1 hyperintense mucinous cavities, T2 hyperintense. Minimal enhancement. High ADC. Low FDG uptake. Mimics benign cystic lesion — FNAB/biopsy is essential for diagnosis.
Criteria
Balanced proportions of mucinous, epidermoid, and intermediate cells. Cystic-solid mixed structure. Moderate atypia and mitosis.
Distinct Features
Cystic-solid mixed structure, heterogeneous enhancement, intermediate ADC values, margins may be partially irregular. Local recurrence and metastasis risk higher than low-grade.
Criteria
Epidermoid cell predominance, solid component >80%, marked atypia, frequent mitosis, necrosis, perineural/vascular invasion. 5-year survival 30-50%.
Distinct Features
Solid dominant, aggressive mass with irregular margins. Low ADC, prominent enhancement, necrosis, peritumoral edema. High FDG uptake (SUVmax >5). Lymph node metastasis common. Differential diagnosis with squamous cell carcinoma and adenoid cystic carcinoma required.
Distinguishing Feature
Pleomorphic adenoma is very markedly hyperintense on T2 (myxoid matrix), high ADC, cystic component is myxoid not mucinous, cystic component not hyperintense on T1 (serous). Capsule is more prominent and smooth.
Distinguishing Feature
Warthin tumor shows Tc-99m pertechnetate uptake (hot nodule — mucoepidermoid does not), specific to parotid tail, may be bilateral/multifocal, T1 hyperintense cystic component is proteinaceous/hemorrhagic (not mucinous), and shows intermediate-to-low T2 signal.
Distinguishing Feature
Adenoid cystic carcinoma is usually solid dominant, perineural spread is the hallmark finding (extension to cranial foramina), no T1 hyperintense cystic component, proportionally more common in submandibular/minor glands, and does not show cystic-solid spectrum unlike mucoepidermoid carcinoma.
Distinguishing Feature
Acinic cell carcinoma is usually a well-defined solid mass, no T1 hyperintense mucinous component, intermediate T2 signal, low ADC but more homogeneous structure, and cystic-solid spectrum differs from mucoepidermoid carcinoma.
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
İİAB veya kor biyopsi ile histolojik tanı ve derecelendirme zorunludur. Cerrahi rezeksiyon primer tedavidir. Yüksek dereceli tümörlerde postoperatif radyoterapi. Servikal lenfadenopati varlığında boyun diseksiyonu. Uzun süreli takip (en az 10 yıl) gereklidir — geç rekürrens ve metastaz riski.Mucoepidermoid carcinoma is a malignant tumor requiring very different prognosis and treatment approaches depending on histological grade. In low-grade tumors, surgical resection (superficial or total parotidectomy) is generally curative with excellent prognosis. In high-grade tumors, wide surgical resection, neck dissection when indicated, and postoperative radiotherapy are performed; prognosis is markedly poor. FNAB can diagnose malignancy but histological grading is usually done on the surgical specimen. Imaging is critical preoperatively for evaluating tumor extent, deep lobe extension, perineural spread, and cervical lymphadenopathy. MAML2 gene fusion is used in diagnosis and prognostic assessment.
Treatment is surgical resection. Adjuvant radiotherapy is added for high-grade forms. Prognosis of low-grade forms is excellent.