Acinic cell carcinoma is a low-grade malignant tumor of salivary glands, accounting for 6-10% of all salivary gland malignancies. It occurs almost exclusively in the parotid gland (90%+). Histologically, it represents neoplastic proliferation of serous acinar cells resembling normal salivary gland acinar cells. It generally presents as a well-defined, solid mass and may mimic pleomorphic adenoma clinically and radiologically. It is slightly more common in females (F:M = 1.5:1). Bilateral involvement may occur in 3-5%. Mean age at diagnosis is 40-50. Prognosis is generally good (90%+ 5-year survival) but long-term follow-up is required due to risk of late recurrence and dedifferentiation. The dedifferentiated variant shows aggressive clinical course. It may be associated with lymphocytic infiltration (lymphocytic variant) and may be related to autoimmune diseases.
Age Range
30-60
Peak Age
45
Gender
Female predominant
Prevalence
Rare
The imaging findings of acinic cell carcinoma are rooted in the relatively homogeneous and well-organized cellular structure of the tumor, which resembles normal serous acinar cells. Acinar cells contain secretory granules that are also present in tumor cells — high protein content affects MR signal characteristics. The well-defined, encapsulated appearance reflects the low-grade growth pattern and creates difficulty in differential diagnosis with benign tumors (especially pleomorphic adenoma). Cellular density differs from the myxoid matrix of pleomorphic adenoma — acinar cells have a more compact arrangement, lowering T2 signal to intermediate levels and reducing ADC. In the lymphocytic variant, dense lymphoid stroma creates additional cellularity and T2 lowering. In the dedifferentiated variant, high cellularity, necrosis, and aggressive growth produce additional imaging findings.
The most distinguishing feature of acinic cell carcinoma is mimicking a benign tumor with its well-defined mass appearance while suggesting malignancy with T2 intermediate signal and low ADC values. This triple combination (well-defined + T2 intermediate + low ADC) clearly separates from pleomorphic adenoma (T2 hyperintense + high ADC) and suggests low-grade malignancy.
On T2-weighted sequences, acinic cell carcinoma shows intermediate signal — this feature clearly differentiates from the marked T2 hyperintensity of pleomorphic adenoma and is the most valuable criterion in differential diagnosis. The compact arrangement and secretory granules of acinar cells shorten T2 time, producing intermediate signal. The tumor generally has a homogeneous signal pattern but focal cystic degeneration or hemorrhage areas may cause heterogeneity. In the lymphocytic variant, lymphoid stroma creates additional T2 lowering. Tumor margins are generally smooth and well-defined — the capsule may be seen as a thin hypointense rim on T2.
Report Sentence
A well-defined solid mass showing intermediate signal on T2-weighted sequences is identified in the parotid gland; unlike the marked T2 hyperintensity of pleomorphic adenoma, this signal level suggests a low-grade malignancy such as acinic cell carcinoma.
On diffusion-weighted imaging, acinic cell carcinoma shows low ADC values (typically 0.8-1.2 × 10⁻³ mm²/s). These ADC values are significantly lower than pleomorphic adenoma (>1.5 × 10⁻³ mm²/s) and are a critical criterion for benign-malignant differentiation in well-defined parotid masses. The compact arrangement of acinar cells and density of secretory granules restrict intracellular water diffusion. ADC, combined with T2 signal, is the most valuable parameter for distinguishing acinic cell carcinoma from pleomorphic adenoma. ADC values may be even lower in the dedifferentiated variant.
Report Sentence
The well-defined parotid mass demonstrates diffusion restriction with low ADC values (ADC: [value] × 10⁻³ mm²/s); despite the well-defined appearance, low ADC values suggest low-grade malignancy, particularly acinic cell carcinoma.
On contrast-enhanced CT, acinic cell carcinoma appears as a well-defined, homogeneously or mildly heterogeneously enhancing solid mass in the parotid gland. CT appearance may be indistinguishable from pleomorphic adenoma — both tumors may appear as well-defined enhancing masses. Calcification may be seen rarely. Bone erosion and invasion of surrounding structures are generally not seen (low grade). On non-contrast CT, the mass has soft tissue density (40-60 HU). In large tumors, focal hypodense areas (cystic degeneration or necrosis) may be observed. Cervical lymphadenopathy is very rare.
Report Sentence
A well-defined solid mass with homogeneous enhancement on post-contrast series is identified in the parotid gland; CT appearance alone is insufficient for benign-malignant differentiation and further characterization with MRI is recommended.
On B-mode ultrasonography, acinic cell carcinoma appears as a well-defined, homogeneous hypoechoic solid mass. This appearance may be indistinguishable from pleomorphic adenoma. The capsule may be identified as a thin echogenic rim. Posterior acoustic enhancement is generally not prominent (solid tumor). Low-to-moderate internal vascularity may be observed on Doppler. Focal cystic areas may be seen in large tumors. US is useful for determining the solid nature, size, and location of the tumor and for FNAB guidance, but insufficient for benign-malignant differentiation.
Report Sentence
A well-defined, homogeneous hypoechoic solid mass is identified in the parotid gland; US appearance overlaps with pleomorphic adenoma and further evaluation with MRI and FNAB is recommended.
On contrast-enhanced T1-weighted sequences, acinic cell carcinoma generally shows homogeneous and prominent enhancement. The well-vascularized acinar structure of the tumor provides contrast distribution. On native T1 sequences, the tumor shows isointense or mildly hypointense signal relative to muscle. The capsule may be seen as a thin, smoothly enhancing rim on post-contrast series. The homogeneous enhancement pattern may differ from pleomorphic adenoma (no enhancement in myxoid areas — heterogeneous) but this difference is not always reliable. In the dedifferentiated variant, heterogeneous enhancement, necrotic areas, and irregular margins are observed.
Report Sentence
The lesion demonstrates homogeneous and prominent enhancement on contrast-enhanced T1-weighted sequences; this enhancement pattern is consistent with a well-vascularized solid tumor.
Criteria
Solid acinar cell arrangement predominant. Most common variant.
Distinct Features
Well-defined, homogeneous solid mass, T2 intermediate, low ADC, homogeneous enhancement. Good prognosis.
Criteria
Dense lymphoid stroma accompanies. Warthin tumor-like lymphoid component but acinar cells instead of oncocytic epithelium.
Distinct Features
More pronounced T2 lowering (lymphoid stroma), may be bilateral, may be associated with autoimmune disease. Distinguished from Warthin tumor by negative pertechnetate.
Criteria
High-grade malignant transformation in a low-grade acinic cell carcinoma background. Aggressive clinical course, poor prognosis.
Distinct Features
Irregular margins, necrosis, very low ADC, heterogeneous enhancement, invasion of surrounding structures, lymph node metastasis. 'Tumor within tumor' appearance.
Distinguishing Feature
Pleomorphic adenoma is markedly T2 hyperintense (myxoid matrix), high ADC (>1.5), benign. Acinic cell carcinoma is T2 intermediate, low ADC (<1.2), malignant.
Distinguishing Feature
Warthin tumor shows Tc-99m pertechnetate hot nodule, cystic-solid mixed, parotid tail, T1 hyperintense cystic component. Acinic cell carcinoma is pertechnetate negative, solid, minimal cystic component.
Distinguishing Feature
Mucoepidermoid carcinoma shows cystic-solid spectrum, T1 hyperintense mucinous cystic component, grade-dependent appearance. Acinic cell carcinoma is usually solid, minimal cystic component, no mucinous content.
Urgency
routineManagement
surgicalBiopsy
NeededFollow-up
İİAB ile tanı konulabilir. Cerrahi rezeksiyon primer tedavi. Süperfisiyal parotidektomi (küçük tümörlerde) veya total parotidektomi (büyük tümörler/derin lob). Radyoterapi seçilmiş olgularda. Uzun süreli takip (en az 10 yıl) — geç rekürrens riski. Dedifferansiye varyantda agresif tedavi.Acinic cell carcinoma is a low-grade malignancy with surgical resection as primary treatment. Prognosis is generally good (90%+ 5-year survival) but long-term follow-up is mandatory due to risk of late recurrence (after 10-15 years) and dedifferentiation. Surgical approach is determined by tumor size and location. Postoperative radiotherapy may be applied in high-risk cases (positive margin, deep lobe extension, large size). FNAB has good diagnostic accuracy but core biopsy or surgical specimen may be needed for definitive differentiation from pleomorphic adenoma. Dedifferentiated variant requires aggressive treatment and close follow-up.
Surgical resection is the primary treatment. Prognosis is generally good. Local recurrence may occur in 35%. Late metastasis is rare but possible.