Salivary gland schwannoma is a benign nerve sheath tumor arising from the intraparotid facial nerve segment (most commonly) or other cranial nerves within the parotid gland. It constitutes 0.5-1.5% of all parotid tumors. The intraparotid segment of the facial nerve is the most common site of origin. Histologically, it consists of Antoni A (compact, palisaded Schwann cells) and Antoni B (loose, myxoid stroma) areas. It is a slow-growing, well-encapsulated tumor. Clinically presents as a painless parotid mass; facial nerve paralysis is rare but may occur in large tumors. Peak incidence between 30-60 years, no gender predilection. May be associated with NF2 (neurofibromatosis type 2) — bilateral vestibular schwannomas may accompany. Malignant transformation is very rare.
Age Range
30-60
Peak Age
45
Gender
Equal
Prevalence
Rare
The imaging findings of schwannoma are based on the different tissue properties of Antoni A and Antoni B areas. Antoni A areas produce intermediate T2 signal with compact Schwann cell arrangement and low water content; Antoni B areas produce hyperintense T2 signal with loose myxoid stroma and high water content. The distribution of these two areas creates the target sign — central Antoni A hypointensity (T2) surrounded by peripheral Antoni B hyperintensity (T2). Since the tumor arises from nerve sheath cells, it follows the nerve course and shows fusiform morphology — it grows eccentrically from the nerve, deforming but generally not invading it. Well-developed capsule creates smooth margins. Gadolinium enhancement is prominent as schwannomas are well-vascularized tumors.
The most characteristic imaging finding of schwannoma is the target sign on T2 (central hypointense Antoni A, peripheral hyperintense Antoni B) and fusiform morphology following the facial nerve course.
On T2-weighted sequences, schwannoma may show target sign: central hypointense region (Antoni A — compact cellular) surrounded by peripheral hyperintense region (Antoni B — myxoid). The tumor has fusiform morphology and follows the facial nerve course. In small tumors, target sign may not be apparent and homogeneous T2 hyperintensity may be seen. In large tumors, cystic degeneration, hemorrhage, and heterogeneity may develop. Overall T2 signal intensity may be similar to pleomorphic adenoma but fusiform morphology and nerve relationship are distinguishing.
Report Sentence
A fusiform mass following the facial nerve course showing target sign on T2-weighted sequences is identified in the parotid gland; consistent with schwannoma.
On post-contrast T1 sequences, schwannoma shows prominent and heterogeneous enhancement. Antoni A areas enhance more intensely while Antoni B areas enhance less. The well-vascularized structure of the tumor explains the prominent enhancement. On native T1, the tumor shows isointense or mildly hypointense signal relative to muscle. Cystic degeneration areas do not enhance.
Report Sentence
The lesion demonstrates prominent and heterogeneous enhancement on post-contrast series; consistent with a well-vascularized nerve sheath tumor.
On CT, schwannoma appears as a well-defined, fusiform, homogeneously or heterogeneously enhancing solid mass. On non-contrast CT, it has soft tissue density (30-50 HU). Cystic degeneration areas appear hypodense. CT cannot demonstrate the tumor's relationship with the facial nerve as well as MRI — MRI is the preferred modality.
Report Sentence
A well-defined, fusiform, enhancing solid mass is identified in the parotid gland; schwannoma is considered and MRI evaluation of facial nerve relationship is recommended.
On B-mode US, schwannoma appears as a hypoechoic, well-defined, fusiform or oval mass. Homogeneous echopattern in small tumors, heterogeneous pattern in large tumors. Cystic degeneration areas appear as anechoic foci. Posterior acoustic enhancement may be observed. Internal vascularity is present on Doppler.
Report Sentence
A hypoechoic, fusiform, well-defined mass is identified in the parotid gland; nerve-origin tumor is considered.
On DWI, schwannoma shows intermediate ADC values (typically 1.0-1.8 × 10⁻³ mm²/s). ADC is high in Antoni B areas, lower in Antoni A areas. ADC values are generally higher than malignant tumors and supportive in benign-malignant differentiation.
Report Sentence
The lesion demonstrates intermediate ADC values on DWI; consistent with nerve sheath tumor.
Criteria
Mixed Antoni A and B areas. Most common type.
Distinct Features
Target sign, fusiform, prominent enhancement, intermediate ADC.
Criteria
Prominent cystic degeneration or hemorrhage. In larger tumors.
Distinct Features
Heterogeneous, cystic areas very T2 hyperintense, solid component enhancement, may mimic pleomorphic adenoma.
Criteria
Developing in NF2 setting, bilateral vestibular schwannomas may accompany.
Distinct Features
Multiple schwannomas, bilateral vestibular, meningiomas may accompany, young age presentation.
Distinguishing Feature
Pleomorphic adenoma is round/lobulated (not fusiform), no target sign, no nerve relationship, T2 markedly hyperintense (homogeneous). Schwannoma is fusiform, target sign, follows nerve course.
Distinguishing Feature
Adenoid cystic carcinoma shows perineural spread (invasion along nerve), irregular margins, T2 intermediate. Schwannoma grows on the nerve but does not invade, well-defined, fusiform.
Distinguishing Feature
Branchial cleft cyst is entirely cystic, no enhancement, EAC relationship. Schwannoma is solid (±cystic degeneration), prominent enhancement, fusiform.
Urgency
routineManagement
surgicalBiopsy
Not NeededFollow-up
Asemptomatik küçük schwannomlar 6-12 aylık MR takip ile izlenebilir. Cerrahi: büyüyen, semptomatik veya fasiyal sinir fonksiyonunu tehdit eden tümörlerde kapsüler enükleasyon veya süperfisiyal/total parotidektomi. Fasiyal sinir korunması kritiktir — intraoperatif elektrofizyolojik sinir monitörizasyonu zorunludur. NF2 taraması yapılmalıdır — bilateral vestibüler schwannom, spinal schwannom, meningiom değerlendirilmelidir. Postoperatif fasiyal sinir fonksiyonu House-Brackmann skalası ile takip edilmelidir.Schwannoma is a benign tumor and surgical decision is based on symptoms and size increase. In small asymptomatic tumors, MRI follow-up may be sufficient. When surgery is needed, capsular enucleation or superficial parotidectomy is performed; facial nerve preservation is critical and intraoperative nerve monitoring is mandatory. In tumors arising from the facial nerve, the nerve may need to be sacrificed — the patient must be informed preoperatively. NF2 should be evaluated — bilateral vestibular schwannomas, meningiomas, and spinal schwannomas should be screened.
Surgical excision is definitive treatment. Facial nerve preservation is important.