Pictorial Essay: Imaging of Peripheral Nerve Sheath Tumours

Median nerve schwannoma in a 35-year-old man, demonstrating the typical fusiform shape with tapered ends. (A) Coronal T1-weighted (W) magnetic resonance (MR) image of the wrist, showing a well-circumscribed fusiform isointense (compared with skeletal muscle) mass with tapered ends that arise from the median nerve at the level of the distal ulna (proximal to the ulna-carpal joint). (B) Coronal T2-W fat-suppressed MR image, showing the fusiform-shaped mass to be of heterogeneously hyperintense T2 signal, more clearly showing it to arise from the median nerve compared with the T1 image. (C) Coronal contrast-enhanced T1-W fat-suppressed MR image, showing heterogeneous enhancement of the mass. (D) Sagittal T2-W fat-suppressed MR image, showing the mass to be eccentric in location in relation to the median nerve, typical of a schwannoma.

Ulnar nerve schwannoma in a 22-year-old woman. (A) Axial T1-weighted (W) magnetic resonance (MR) image, showing a well-circumscribed isointense (compared with skeletal muscle) mass arising from the ulnar nerve at the level of the distal ulna (proximal to the ulnar-carpal joint). (B) Axial T2-W fat-suppressed MR image, showing the lesion to be heterogeneously hyperintense. (C) Axial contrast-enhanced T1-W MR image, showing mild heterogeneous enhancement. (D) Photomicrograph (H&E, original magnification × 20) of the excised specimen confirms the diagnosis of schwannoma.

Tibial neurogenic tumour in a 48-year-old man. (A) Coronal proton-density magnetic resonance (MR) image, showing a well-circumscribed mass that is slightly hyperintense compared with skeletal muscle; it arises from the tibial nerve. (B) Axial T2-weighted (W) fat-suppressed MR image, showing the lesion to be homogeneously hyperintense. (C) Coronal contrast–enhanced T1-W fat-suppressed MR image, showing a homogeneous avidly enhancing solid mass arising from the tibial nerve medial to the talo-calcaneal joint.

Anterior deltoid intramuscular schwannoma in a 21-year-old man, demonstrating the classic split-fat sign and the target sign. (A) Coronal T1-weighted (W) magnetic resonance (MR) image, showing a well-circumscribed ovoid isointense mass (compared with the skeletal muscle) within the right deltoid muscle. The tapered rim of hyperintense fat is seen adjacent to the proximal and distal ends of the lesion. (B) Coronal T2-W fat-suppressed MR image, showing peripheral hyperintense T2 signal intensity, whereas the central area of the lesion is more hypointense, demonstrating the target sign. (C) Coronal contrast-enhanced T1-W fat-suppressed MR image, showing heterogeneous enhancement that is less avid peripherally. (D) Axial T2-W fat-suppressed MR image, again demonstrating the target sign, which consists of peripheral hyperintensity and central hypointensity. (E) Axial contrast-enhanced T1-W fat-suppressed MR image, showing predominantly central heterogeneous enhancement.

Intramuscular schwannoma in a 26-year-old man who presented with a painless mass in the posterior compartment of the left thigh, with images demonstrating a classic split-fat sign. (A) Sagittal T1-weighted (W) magnetic resonance (MR) image, showing a well-circumscribed ovoid heterogeneous mass (slightly hyperintense compared with the skeletal muscle) located within the semitendinosus muscle. The tapered rim of hyperintense fat is seen adjacent to the proximal and distal ends of the lesion, typical of the split-fat sign. (B) Sagittal TIRM MR image, showing the lesion to be heterogeneously hyperintense; the adjacent split-fat sign is present.

Ulnar and median neurofibromas in a 15-year-old girl, with images demonstrating the magnetic resonance (MR) fascicular sign. (A) Sagittal T1-weighted (W) MR image, showing a well-circumscribed elongated mass arising from the median nerve at the level of the carpal bones, which is isointense to skeletal muscle. (B) Sagittal T2-W fat-suppressed MR image, showing the lesion to be heterogeneous hyperintense, with thickened hypointense strands within. (C) Axial T1-W MR image, showing 2 well-circumscribed isointense lesions, which correspond to the volar-sided nerves of the wrist; the more radial lesion is the median neurofibroma, whereas the more ulnar lesion is the ulnar neurofibroma. (D) Axial T2-W fat-suppressed image, showing the median and ulnar neurofibromas as hyperintense masses with speckled central areas of hypointense foci; these represent thickened fascicles. (E) Coronal T2-W fat-suppressed MR image, showing both the median and ulnar neurofibromas in the same plane. (F) Axial contrast-enhanced T1-W fat-suppressed MR image, showing heterogeneously enhancement of the ulnar and median neurofibromas.

Thenar intramuscular schwannoma in a 74-year-old man. (A) Radiograph of the left hand, showing a vague nonspecific soft-tissue mass in the first web space, with no abnormal bony changes. (B) Axial T1-weighted (W) magnetic resonance (MR) image of the left hand, showing a heterogeneously hyperintense nonspecific lobulated mass (compared with skeletal muscle) located within the thenar muscle. (C) Axial T2-W fat-suppressed MR image, showing the well-circumscribed lesion to be heterogeneously hyperintense. (D) Axial contrast-enhanced T1-W fat-suppressed MR image, showing heterogeneous enhancement of the lesion. There are no specific features to suggest a neurogenic tumour, and pathologic examination is required. Diagnosis of thenar schwannoma was confirmed, by histologic examination, after excision.