An incidental finding: a benign schwannoma

Clinical History

A 58-year-old woman came to our hospital to undergo a presurgical evaluation for possible kidney donation to her son. She did not have relevant medical history and her physical exploration and laboratory tests were normal.

Imaging Findings

Posteroanterior (PA) and lateral (L) chest radiographs were performed. A lesion projected over the left hilium was observed in the PA view. The lesion did not obscure hiliar vessels (Fig 1). Lateral view revealed that the mass was located in the posterior aspect of the left hemithorax. Smooth margins conforming obtuse angles delineated the mass in both views, suggesting an extrapulmonary lesion (Fig 2). Computed tomography (CT) without and after intravenous contrast medium revealed a six centimetre left extrapulmonary mass which did not show enhancement after contrast medium administration. It was still quite hypodense in the latter ten minute acquisition. There was no evidence of adjacent rib erosion. No relationship with the vertebral foramen was established (Fig 3, 4, 5) . An ultrasound-guided biopsy was performed to confirm the suspected diagnosis. The histological study revealed a tumour constituting of spindle-cells expressing S-100 protein suggestive of a typical benign schwannoma.

Discussion

Neurogenic tumours (NT) are the most frequent cause of posterior mediastinum masses, accounting for more than 90% of them [1]. They can be subdivided in three groups according to the neurological structures where they originate. They can derive from nerve root (schwannomas and neurofibromas), sympathetic ganglion (neuroblastomas, ganglioneuroblastomas, ganglioneuromas) and paragangliomas (chemodectomas and pheochromocytomas) [2]. NT are usually diagnosed in middle-aged patients, without no sex predominance [2], the most common location being the thorax and the posterior mediastinum.
The most frequent type of neurogenic tumours are benign schwannomas. Schwannoma or neurinoma derive from the peripheral nerve and they are formed by Schwann cells [3]. Histological studies of schwannomas are composed of spindle cells arranged in fascicles. Inmunohistochemical tests help us to confirm the diagnosis because S100 protein is strongly expressed by most of these tumours [4].
Schwanommas are often asymptomatic, and they are usually diagnosed when an imaging procedure is performed for other reasons. The presence of symptoms raises the suspicion of malignancy [2].
These tumours may occasionally be associated with bone and central nervous system lesions; when it infiltrates the whole nerve trunk we have to consider the Von Recklinghausen’s disease as a possible diagnosis [3].
The first imaging technique in a patient with a lesion in the posterior mediastinum must be posteroanterior chest radiography, [5] where deformation of mediastinal contours and line displacement of normal structures can be observed.
Computed tomography (CT) and magnetic resonance (MR) are good techniques that provide important information of mediastinal masses, concerning the extent of neoplasm and its relationship to vascular and mediastinal structures [6]. On CT, schwannomas are well-defined, homogeneous or heterogeneous masses. Schwannomas usually have similar density to muscle. They may be seen as areas of low attenuation on non-contrast CT when they have high concentration of lipid-rich Schwann cells [7]. Schwannomas can show a homogeneous, heterogeneous or peripheral enhancement after contrast administration [4]. The relationship with vertebraes, ribs, and spinal canal are essential for planning therapy.
MRI is also indicated in patients suspected for a neurogenic tumour, because it allows investigation of the intraspinal extension of the tumour.
In all of these cases, imaging techniques (CT and MRI) play an essential role. Ultrasound may also be useful for performing biopsy.
The principal treatment of choice of schwannomas is surgery by thoracoscopy or thoracotomy because the tumour will continue to increase in size if left untreated [2]. Patients with benign neurogenic tumours have an excellent prognosis [3].

Differential Diagnosis List

Final Diagnosis

A benign schwannoma

URL:	https://eurorad.org/case/10610
DOI:	10.1594/EURORAD/CASE.10610
ISSN:	1563-4086