Adenoid cystic carcinoma (ACC) is a malignant neoplasm of minor salivary gland origin, slow-growing but with high perineural spread (PNS) capacity. It accounts for approximately 10-15% of all sinonasal malignancies and most commonly originates from the maxillary sinus and nasal cavity. Histopathologically, cribriform (most common — 30-40%), tubular, and solid subtypes exist; the solid subtype has the worst prognosis. ACC's distinguishing feature is its prominent perineural spread capacity — PNS is present in 40-60% of patients and this spread can extend retrogradely along V2 (infraorbital nerve) or V3 (mandibular nerve) to the cavernous sinus. Clinical course is indolent, characterized by local recurrence and late distant metastasis (especially lung — 30-40%). 5-year survival is 60-70%, but 15-20 year survival drops to 20-30% because late recurrences are common. Accurate detection of perineural spread on MRI is critically important in treatment planning.
Age Range
40-70
Peak Age
55
Gender
Equal
Prevalence
Rare
ACC originates from the ductal and myoepithelial cells of minor salivary glands beneath the sinonasal mucosa; MYB-NFIB gene fusion (t(6;9)) is detected in 80% of cases and constitutive activation of the MYB transcription factor sustains tumor proliferation. The tumor's prominent perineural spread capacity results from the interaction of tumor cells with nerve sheath components — neural cell adhesion molecule (NCAM), nerve growth factor receptor (NGFR/p75NTR), and laminin-5 expression increase tumor cell adhesion and migration capacity to the perineural space. The perineural space provides a low-resistance path for tumor cells because nerve sheath fibrous tissue barriers are more lax than perivascular spaces. In the cribriform histological pattern, tumor cells form pseudolumina surrounded by basement membrane material — this structure may translate to T2 hyperintense small cystic foci on MRI. In the solid subtype, dense cellular proliferation is associated with more aggressive growth pattern and lower ADC values. Late distant metastases (can appear even 10-20 years later) occur through hematogenous spread and most commonly affect the lung — this slow but persistent biological behavior mandates long-term follow-up in the clinical management of ACC.
Disproportionately extensive perineural spread relative to the primary tumor size is ACC's most distinguishing radiological feature. When enhancing nerve thickening extending from the pterygopalatine fossa to Meckel's cave along V2 or V3 is seen accompanying a small sinonasal mass, it strongly suggests ACC diagnosis. This disproportion reflects ACC's much more prominent neurotropic spread capacity compared to SCC or other malignancies.
On fat-suppressed contrast-enhanced T1 sequences, the most distinguishing finding of ACC, prominent perineural spread (PNS), is observed. Nerve thickening, pathological enhancement, and surrounding fat plane obliteration along V2 (infraorbital nerve) and/or V3 (mandibular nerve) are seen. PNS spread pathways: V2 → infraorbital canal → pterygopalatine fossa → foramen rotundum → Meckel's cave → cavernous sinus | V3 → foramen ovale → Meckel's cave → cavernous sinus. Replacement of normal fat signal in the pterygopalatine fossa with enhancing tissue is an early PNS finding. Widening of foramen rotundum or foramen ovale is an accompanying finding on CT. In ACC, PNS can spread to distant locations from the primary tumor ('skip lesions' — discontinuous spread possible), and therefore careful evaluation along the entire nerve tract is required.
Report Sentence
On fat-suppressed contrast-enhanced T1 sequences, prominent nerve thickening and pathological enhancement along the left/right infraorbital nerve (V2) / mandibular nerve (V3) is noted, consistent with extensive perineural tumor spread; spread at the levels of pterygopalatine fossa / foramen rotundum / Meckel's cave is present.
On T2-weighted sequences, ACC shows heterogeneous signal related to histological subtype. In the cribriform subtype, a mixture of T2 hyperintense small cystic foci (pseudolumina — microscopic spaces surrounded by basement membrane material) and T2 intermediate solid component is seen within the tumor. In the tubular subtype, tubular structures may be T2 hyperintense. In the solid subtype, more homogeneous intermediate T2 signal is seen because cystic areas are few. T2 heterogeneity may help differentiate ACC from SCC and lymphoma, which show more homogeneous T2 signal. In areas of perineural spread, nerve thickening may be seen as slightly hyperintense on T2.
Report Sentence
On T2-weighted sequences, the mass shows heterogeneous signal with a mixture of T2 hyperintense small cystic foci and intermediate solid component within the tumor.
On CT, ACC demonstrates bone destruction but it may be less aggressive compared to SCC, reflecting the slow growth pattern. Bone destruction is of lytic type and indicates local invasion of the tumor. Particularly notable in ACC is perineural foraminal widening: widening and surrounding bone erosion may be seen in the foramen rotundum (V2 pathway), infraorbital canal, foramen ovale (V3 pathway), or vidian canal. Foraminal widening may indicate clinically occult perineural spread, and therefore systematic evaluation of foramina along nerve tracts is mandatory. Pterygopalatine fossa widening and replacement of fat density with soft tissue density are also among CT findings of PNS.
Report Sentence
A mass with lytic bone destruction is noted in the left/right maxillary sinus, with widened foramen rotundum / infraorbital canal consistent with perineural spread.
On DWI, ACC shows moderate diffusion restriction in cribriform and tubular subtypes (ADC typically 0.9-1.2 × 10⁻³ mm²/s). In the solid subtype, more pronounced restriction is seen (ADC <0.9 × 10⁻³ mm²/s). These intermediate ADC values may help differentiate ACC from highly cellular tumors (SCC: <0.8, lymphoma: <0.7). The cystic components of the cribriform pattern increase ADC while the solid component decreases ADC, resulting in an average ADC at the voxel level. DWI can be used in treatment response assessment: ADC values increase after successful treatment. DWI sensitivity is limited in areas of perineural spread because thin tumoral tissue along small nerve branches may be below DWI spatial resolution.
Report Sentence
Moderate diffusion restriction is noted in the mass on DWI with intermediate ADC values (approximately ... × 10⁻³ mm²/s).
On contrast-enhanced CT, ACC demonstrates moderate homogeneous or mildly heterogeneous solid enhancement. Enhancement is generally more homogeneous than the markedly heterogeneous enhancement of SCC and necrotic areas are fewer. In the cribriform subtype, microscopic cystic areas within the tumor may be below CT spatial resolution and the mass exhibits a homogeneous solid appearance. Contrast-enhanced CT provides preliminary assessment of primary tumor extent but is significantly inferior to MRI in detecting perineural spread and therefore should always be supplemented with MRI in ACC.
Report Sentence
On contrast-enhanced CT, the mass shows moderate homogeneous solid enhancement with no significant necrotic area identified.
On FDG PET-CT, ACC shows moderate FDG uptake (SUVmax typically 4-8 — lower than SCC's typically >8 values). This lower metabolic activity reflects ACC's indolent biological behavior and slow proliferation rate. PET-CT is used for metabolic evaluation of the primary tumor as well as distant metastasis screening (especially lung) and treatment response assessment. FDG uptake may be very low in low-grade ACCs with risk of false-negative results. Periodic PET-CT follow-up may be useful for screening late distant metastases (even after 10-20 years).
Report Sentence
On FDG PET-CT, moderate FDG uptake is noted in the mass (SUVmax: ...); distant metastatic focus in the lung is present/not identified.
Criteria
Most common subtype (30-40%). Characterized by 'Swiss cheese'-like pseudolumina. Best prognosis.
Distinct Features
Small cystic foci on MRI T2 (hyperintense), intermediate ADC values, moderate enhancement. 10-year survival 50-60%.
Criteria
Characterized by tubular glandular structures. Good prognosis — similar to cribriform.
Distinct Features
Tubular structures may be T2 hyperintense on MRI. Perineural spread capacity similar to cribriform.
Criteria
Dense solid cellular proliferation, minimal cystic areas. Worst prognosis. 20-30% of all ACCs.
Distinct Features
More homogeneous intermediate T2 signal on MRI, low ADC (<0.9), more prominent enhancement, more aggressive bone destruction. 10-year survival 20-30%.
Distinguishing Feature
SCC shows more aggressive bone destruction, gives lower ADC values on DWI (<0.8), contains more necrosis, and perineural spread is less frequent and less extensive than ACC. SCC more commonly destroys the maxillary sinus posterior wall.
Distinguishing Feature
Lymphoma shows very low ADC (<0.6-0.7), demonstrates homogeneous enhancement, exhibits 'bone replacement' pattern (bone marrow infiltration without bone destruction), and does not show perineural spread.
Distinguishing Feature
Olfactory neuroblastoma originates from the cribriform plate (ACC more commonly originates from the maxillary sinus/nasal cavity lateral wall), shows dumbbell shape (intracranial + intranasal), may contain peripheral cystic component (cyst on nasal cavity side), and perineural spread is rare.
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
Uzun süreli takip zorunludur: ilk 5 yıl 6 ayda bir MRG + göğüs BT; 5-20 yıl arası yıllık MRG + göğüs BT. Geç rekürrens (>10 yıl) sık olduğundan ömür boyu takip önerilir.Wide surgical resection + adjuvant radiotherapy (proton or photon) is the standard approach in ACC treatment. Negative surgical margins are critical but difficult to achieve due to perineural spread. The radiotherapy field must cover the perineural spread route — irradiation up to the cavernous sinus is required in the presence of intracranial PNS. The role of chemotherapy is limited; cisplatin-based regimens are used in advanced and metastatic disease. Late distant metastasis risk (especially lung) is 30-40%, and slow-growing lung nodules may remain stable for years — surgical metastasectomy may provide survival advantage in appropriate cases. 5-year survival 60-70%, 10-year 40-50%, 15-20 year 20-30%.
ACC treatment is wide surgical resection + adjuvant radiotherapy. Safe surgical margins are difficult due to perineural spread. Local recurrence rate is high. Distant metastasis (lung) can develop years later — requires long-term follow-up. 10-year survival is 50-70%.