Adenoid cystic carcinoma (AdCC) is the second most common malignant tumor of salivary glands, accounting for 10-15% of all salivary gland malignancies. Its most important and distinguishing feature is perineural spread — the tumor can spread along nerve sheaths to reach the skull base. It is proportionally more common in the submandibular gland and minor salivary glands (palate, tongue base, nasal cavity) compared to the parotid. Histologically, three growth patterns are defined: cribriform (most common), tubular, and solid; the solid pattern has the worst prognosis. The tumor grows slowly but is highly aggressive: local recurrence rate is high, late distant metastasis (especially lung) is characteristic, and metastasis can appear even 10-20 years after diagnosis. While 5-year survival is 60-70%, 15-year survival drops to 25-35%. It can occur at any age but peaks between 40-60 years, with equal frequency in males and females.
Age Range
40-70
Peak Age
55
Gender
Female predominant
Prevalence
Uncommon
The imaging findings of adenoid cystic carcinoma are based on the tumor's strong perineural trophism and histological structure. Tumor cells invade the perineural space of nerve sheaths and advance in the space between Schwann cells and basal lamina; this perineural spread manifests on imaging as an enhancing tubular structure along the nerve and may show extension to skull base foramina (foramen ovale, foramen rotundum, stylomastoid foramen). On MRI, thickening and abnormal enhancement of the nerve course is the most sensitive imaging finding for this spread. In the cribriform histological pattern, pseudocystic spaces (not true cysts, filled with basement membrane material) may produce T2 hyperintensity but not as bright as pleomorphic adenoma. High cellularity in the solid component manifests with diffusion restriction. The tumor's infiltrative growth pattern into surrounding tissues creates irregular margins and desmoplastic reaction; this can be seen as T2 hypointensity.
The hallmark finding of adenoid cystic carcinoma is perineural spread — the tumor can spread along nerve sheaths to skull base foramina and the intracranial space. It is seen as abnormal thickening and enhancement of the nerve course on post-contrast fat-suppressed T1 MRI. This finding is not expected in other salivary gland tumors (pleomorphic adenoma, Warthin tumor) and is nearly pathognomonic for adenoid cystic carcinoma.
Post-contrast fat-suppressed T1-weighted MRI is the most valuable sequence for demonstrating perineural spread in adenoid cystic carcinoma. Perineural spread is seen as thickening and abnormal enhancement of the affected nerve, and loss of normal hypointense signal in surrounding fat on fat-suppressed sequences. The facial nerve (CN VII) is the most commonly involved nerve in parotid tumors — it can be traced from the stylomastoid foramen into the temporal bone and to the cerebellopontine angle. Trigeminal nerve branches (CN V — especially V2 and V3) are involved in submandibular and palatal tumors — extension along foramen ovale and foramen rotundum to the cavernous sinus may be demonstrated. Perineural spread may be asymptomatic and subclinical spread on imaging may extend far beyond the primary tumor.
Report Sentence
On post-contrast fat-suppressed T1 sequences, abnormal enhancement and nerve thickening extending from the tumor and following the course of [nerve name] is identified; this finding is consistent with perineural spread and characteristic of adenoid cystic carcinoma.
On T2-weighted sequences, adenoid cystic carcinoma generally shows intermediate signal. In cribriform and tubular histological patterns, focal T2 hyperintensities may be seen due to pseudocystic spaces, but these differ from the marked, homogeneous hyperintensity of pleomorphic adenoma. In the solid pattern, T2 signal is lower, reflecting cellular density. Desmoplastic stroma shows T2 hypointensity — this finding supports the infiltrative growth pattern. Infiltration into surrounding tissues can be seen as T2 signal loss in normal anatomy. Nerve segments showing perineural spread may demonstrate focal thickening on T2.
Report Sentence
A solid mass with irregular margins showing intermediate signal on T2-weighted sequences is identified in the salivary gland; unlike pleomorphic adenoma, T2 hyperintensity is not prominent and a malignant salivary gland tumor, particularly adenoid cystic carcinoma, should be considered.
On diffusion-weighted imaging, adenoid cystic carcinoma generally shows diffusion restriction; ADC values are low (typically 0.7-1.1 × 10⁻³ mm²/s). ADC values are lowest in the solid pattern and may be relatively higher in the cribriform pattern. Diffusion restriction may also be seen in nerve segments showing perineural spread — this finding may help detect subclinical perineural spread that is difficult to see on conventional MRI. ADC values are clearly lower than pleomorphic adenoma (>1.5 × 10⁻³ mm²/s) and are in a similar range to other malignant salivary gland tumors.
Report Sentence
Diffusion restriction and low ADC values are observed in the lesion (ADC: [value] × 10⁻³ mm²/s), supporting malignant salivary gland tumor, particularly adenoid cystic carcinoma.
On contrast-enhanced CT, adenoid cystic carcinoma appears as an irregularly margined, heterogeneously enhancing solid mass. The tumor shows infiltrative growth into surrounding structures — obliteration of fat planes, bone erosion/destruction are important CT findings. Bone erosion in the palate or maxilla is common in minor salivary gland tumors. Widening of skull base foramina may be a CT finding of perineural spread — widening of foramen ovale, foramen rotundum, and stylomastoid canal should be evaluated. Calcification is rare and its presence is not specific for AdCC. Cervical lymphadenopathy is less common in AdCC than in other malignant tumors (10-15%) — distant metastasis occurs hematogenously.
Report Sentence
An irregularly margined, heterogeneously enhancing solid mass obliterating surrounding fat planes and showing bone erosion is identified in the salivary gland; widening of skull base foramina suggests perineural spread and adenoid cystic carcinoma should be primarily considered.
On B-mode ultrasonography, adenoid cystic carcinoma typically appears as a hypoechoic, heterogeneous, irregularly margined solid mass. Tumor margins may be indistinct due to infiltration into surrounding structures. Internal vascularity may be increased on Doppler. Cystic areas may be rarely seen (cribriform pattern). US is useful for initial evaluation of tumors in the submandibular gland but is insufficient for demonstrating perineural spread and skull base extension — MRI is mandatory. US is helpful in evaluating cervical lymph nodes (although lymph node metastasis is rare in AdCC). US is used for FNAB guidance.
Report Sentence
An irregularly margined, hypoechoic, heterogeneous solid mass is identified in the salivary gland with increased internal vascularity on Doppler examination; malignant salivary gland tumor is suspected and MRI is recommended for evaluation of perineural spread and skull base extension.
On non-contrast CT, widening of skull base foramina is an indirect but important finding of perineural spread in adenoid cystic carcinoma. Widening of the foramen ovale (V3 branch), foramen rotundum (V2 branch), stylomastoid foramen (CN VII), Vidian canal (Vidian nerve), and hypoglossal canal (CN XII) should be evaluated. These foramina are compared with the contralateral side to detect asymmetry. Bone window reconstructions should be created from thin-section data. Foraminal widening indicates that perineural spread has reached the skull base and intracranial extension potential — critical information for surgical planning and prognosis.
Report Sentence
On bone window reconstructions, ipsilateral [foramen name] widening is identified compared to the contralateral side; this finding is consistent with perineural spread and demonstrates skull base extension in the context of adenoid cystic carcinoma.
Criteria
Sieve-like (cribriform) growth pattern predominant. Most common histological type (40-50%). Pseudocystic spaces filled with basement membrane material.
Distinct Features
Intermediate-to-high T2 signal (pseudocystic spaces), heterogeneous enhancement, intermediate ADC. Moderate aggressiveness, 5-year survival 60-70%.
Criteria
Tubular/trabecular growth pattern predominant. Type with the best prognosis. Less common (20-30%).
Distinct Features
Relatively better-defined, more homogeneous enhancement, ADC values higher than solid pattern. Best prognosis — 5-year survival >80%.
Criteria
Solid island growth pattern predominant (>30% solid component). Most aggressive type. Less common (20-30%).
Distinct Features
Solid, irregular-margined mass, marked diffusion restriction (lowest ADC), intermediate-to-low T2 signal, prominent enhancement, necrosis, aggressive growth. Worst prognosis — 5-year survival 30-40%.
Distinguishing Feature
Mucoepidermoid carcinoma does not show perineural spread (or very rarely), shows cystic-solid spectrum (low-grade: cystic dominant), contains T1 hyperintense mucinous cystic component, and is more common in parotid. Adenoid cystic carcinoma is solid dominant and perineural spread is the hallmark finding.
Distinguishing Feature
Pleomorphic adenoma is benign, well-defined, markedly T2 hyperintense (myxoid matrix), high ADC, no perineural spread, encapsulated. Adenoid cystic carcinoma has irregular margins, intermediate T2, low ADC, shows perineural spread.
Distinguishing Feature
Chronic sclerosing sialadenitis (Küttner tumor) may show similarity as a hard mass in the submandibular gland but perineural spread is absent, diffuse T2 hypointensity (fibrosis), may be bilateral, may be IgG4-related, and ADC values are intermediate-to-high.
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
Cerrahi rezeksiyon primer tedavidir. Perinöral yayılım nedeniyle geniş cerrahi sınırlar gereklidir. Postoperatif radyoterapi (proton tedavisi dahil) standart olarak uygulanır. Uzun süreli takip zorunludur — minimum 15-20 yıl (geç rekürrens ve metastaz). Toraks BT ile akciğer metastazı taranmalıdır.Adenoid cystic carcinoma is an aggressive malignant tumor requiring surgical resection and postoperative radiotherapy. Due to perineural spread, surgical margins must be wide and negative nerve margins should be confirmed with frozen sections. In the presence of skull base extension, surgery becomes more complex and requires a multidisciplinary approach. Postoperative radiotherapy improves local control; proton therapy may be preferred for skull base tumors. Chemotherapy has limited efficacy. Distant metastasis (especially lung) may appear late — even 10-20 years after diagnosis. Therefore, follow-up for at least 15-20 years is mandatory and periodic chest CT for lung screening should be performed. MYB-NFIB gene fusion is a diagnostic and potential therapeutic target.
Wide surgical resection + adjuvant radiotherapy is standard treatment. Local recurrence is common (40%) due to perineural spread. Pulmonary metastasis may develop 10-20 years later.