Schwannoma of the Posterior Interosseous Nerve

Abstract

An 80-year-old male patient with a history of renal cell carcinoma presented to his primary care physician with a painless lump in his left upper extremity. Physical examination revealed a 3-cm nonmobile, nontender soft-tissue mass in the left forearm. Radiographs showed an abnormal soft tissue contour along the posterolateral aspect of the mid forearm without underlying osseous changes (Fig. 1). An ultrasound of the posterior aspect of the mid forearm revealed a well-defined, hypoechoic lesion with intrinsic blood flow, posterior acoustic enhancement, and a thin echogenic rim surrounding the lesion, consistent with a split fat sign (Fig. 2). Echogenic structures were observed entering and exiting the mass (Fig. 3), suggestive of an enlarged posterior interosseous nerve (normal ultrasound appearance of the posterior interosseous nerve is provided for comparison in Fig. 4). A nerve block of the posterior interosseous nerve was performed, followed by an ultrasound-guided percutaneous biopsy of the mass. Pathology showed Antoni A and Antoni B architectural patterns on hematoxylin-eosin stain (Fig. 5).

Schwannoma of Posterior Interosseous Nerve: A Case Report and Review of Literature

“…As these are slow growing benign lesion, hardly any symptoms appear in early period. As the size increases, symptoms become apparent 2 . Also, the slow-growing nature of tumor allows nerve fibers to adapt themselves to pressure effect, so there is further delay in presentation of the patient to health facility 5 .…”

Peripheral Nerve Schwannomas: A Literature Review

“…2 In contrast to schwannomas, neurofibromas do not contain Antoni A and Antoni B regions, and are less likely to show myelogenous and degenerative areas. 12 Secondary degenerative changes of the tumor can be shown and characterized by the formation of cysts, hyalinization, hemorrhage and calcification. However, degeneration of the ossification is extremely rare.…”

“…On ultrasonography (US), most PNSTs, including schwannomas, are hypoechogenic and have posterior acoustic reinforcement, making them look like a ganglion cyst, which can also be observed in other tumors of uniform cellularity, such as lymphomas. 5,11,12 The presence of blood flow on the Doppler can distinguish a PNST from a cystic lesion. 5 On US, schwannomas appear as well-defined, ovoid, heterogeneous masses together with cystic degeneration and eccentric location.…”

“…11 Although magnetic resonance imaging (MRI) and US can be used to aid in the differentiation between benign and malignant tumors, these techniques are not consistently reliable; however, it is possible to identify signs of degeneration of long-standing tumors by features such as calcifications. 5,12 (►Fig. 3)…”

“…The MRI enables the identification and characterization of lesions with neural involvement, their relation to important anatomical structures, and the extent of intrinsic or extrinsic nerve involvement. 5,11,12 The lesion is typically visualized as a well-defined mass of fusiform shape, located within the nerve, iso-or hypointense in the signal related to the skeletal muscle in T1-weighted images, and with increased signal intensity and slightly heterogeneous in T2-weighted images 11,13 (►Fig. 5A and 5B).…”