Incidental ancient schwannoma of the posterior mediastinum in a young male: a rare scenario

Abstract

Ancient schwannoma is a distinctive type of schwannoma occurring mostly in the retroperitoneum. The presentation in the posterior mediastinum is rare. The term ‘ancient’ represents a group of neurogenic tumours showing degenerative changes with marked nuclear atypia. A 26-year-old man was incidentally detected to have an upper mediastinal mass lesion in the chest X-ray. MRI chest revealed a mixed signal intensity lesion in the left side upper para spinal region of the posterior mediastinum. The patient underwent left posterior thoracotomy and excision of the mass was done. Postoperative period was uneventful. The histopathological feature was typical of Ancient schwannoma. The patient is on regular follow-up and disease free until.

Background

Neurogenic tumour schwannoma mostly (45%) occur in the head and neck and about 9% in the mediastinum.¹ Ancient schwannoma is a distinctive type of schwannoma constituting about 0.8% of soft tissue tumours.² Ancient schwannoma in the posterior mediastinum is an extremely rare presentation. Only few cases have been reported in the world literature.³ Here we describe an incidentally detected ancient schwannoma in a young male detected on the routine evaluation of dyspepsia. This is the first case described in a young man in the world literature.

Case presentation

A 26-year-old man was evaluated for dyspepsia of 2-year duration. The patient had vague upper back pain of similar duration. No history of breathlessness or haemoptysis. No history of significant weight loss or loss of the appetite. No history of fever. No history of smoking or alcohol intake. General physical examination was within normal limits. Respiratory examination revealed a mild decrease in breath sounds in the left upper interscapular region. Abdominal examination revealed no organomegaly.

Investigations

Routine chest X-ray revealed upper mediastinal mass with mediastinal widening (figure 1). The patient underwent CT chest at outside centre 6 months prior which showed 7.4 cm*6.5 cm*5.6 cm well-circumscribed heterodense lesion in the left upper posterior mediastinum (figure 2). He was suggested further evaluation but defaulted subsequently. MRI chest did now revealed a 7.4 cm*6.5 cm*5.6 cm well-encapsulated mixed signal intensity lesion noticed in the left side para spinal region with the epicentre from the left third intercostal nerve abutting the trachea, aortic arch and subclavian vessels without radiological evidence of infiltration. The adjacent left upper lobe of lung was compressed (figure 3).

Figure 1.

Chest X-ray showing a smooth upper mediastinal mass causing mediastinal widening.

Figure 2.

CT chest showing a well-circumscribed heterodense lesion in the left upper mediastinum abutting subclavian vessels and trachea.

Figure 3.

MRI showing mixed signal intensity lesion with intralesional haemorrhages and haemorrhagic fluid level noticed in the left side para spinal region compressing adjacent lung parenchyma.

Differential diagnosis

Posterior mediastinal masses including schwannoma, lymphoma, and mediastinal germ cell tumours were considered. The long duration of history and absence of systemic symptoms without generalised lymphadenopathy were against the diagnosis of lymphoma. Serum lactate dehydrogenase (LDH) was normal. Tumour markers for mediastinal germ cell tumor (GCT) and nonseminomatous germ cell tumor (NSGCT) including serum Beta HCG, serum AFP, and serum LDH were within normal limits. In view of long duration of history, static tumour size of nearly 6 months and well-encapsulated lesion on imaging, a benign neurogenic tumour was considered. Tissue diagnosis by fine needle aspiration cytology (FNAC)/Trucut biopsy was not planned in view of benign biological behaviour of the tumour.

Treatment

The patient underwent left posterior thoracotomy in the third intercostal space. The mass was dissected all around and feeders from subclavian vessels were ligated. Excision of the mass was done in toto without spill (figure 4). Postoperative period was uneventful. Macroscopically, the mass was grey-brown measuring 7.4 cm*6.5 cm*5.6 cm. The external surface was completely encapsulated, grey-brown and smooth. The cut surface showed both solid and cystic areas (70% solid and 30% cystic) (figure 5). Microscopy showed a well-circumscribed lesion composed predominantly of spindle cells with wavy nuclei arranged in hypocellular and hypercellular areas with cystic changes. There were dense eosinophilic Antoni A areas and loose pale Antoni B areas showing spindle cells with wavy nuclei and thick-walled blood vessels. There were focal areas with peripheral palisading of nuclei forming Verocay bodies (figure 6). Immunohistochemistry was strongly positive for S-100 and Ki-67 was 1% (figure 7). The histopathological feature was typical of ancient schwannoma.

Figure 4.

Well-circumscribed mass in the posterior mediastinum after excision with an adjacent ruler.

Figure 5.

Gross – cut surface of a single globular grey-brown mass, well encapsulated, solid (70%) and cystic (30%) with focal myxoid areas.

Figure 6.

Anuclear zones resulting in Verocay bodies formed by nuclear regimentation (×200).

Figure 7.

IHC for S-100 strongly positive in the tumour cells confirming neural origin (×100). IHC, immunohistochemistry.

Outcome and follow-up

The patient is on regular follow-up and disease free until.

Discussion

Schwannoma arises from Schwann cells of the neural sheath.¹ Schwannoma is the the most common of the posterior mediastinal tumours. Commonly arising from the intercostal nerves of the posterior mediastinum, Schwannomas are situated in the paravertebral location. Mostly they are single lesions in the costovertebral sulcus, though rarely they may present as multiple lesions.³ A group of neural tumours showing degenerative changes and marked nuclear atypia were termed as ‘ancient’. They usually occur as solitary tumours.⁴ Ancient schwannoma showed advanced degenerative changes including calcification, hyalinisation and cavitations consistent with a long-standing tumour.⁵ Schwannomas occur in the third and fourth decades of life and distributed equally in both sexes.⁶ Our patient is 26 years old and is the first young man with ancient schwannoma of posterior mediastinum described in the world literature so far.

The tumour contains varying proportions of Antoni A and B histologies on microscopy. Antoni A comprises spindle cells with elongated nuclei, forming interlacing bundles with focal nuclear palisading. Antoni A lacks mitotic figures. Antoni B is less cellular lacking distinct architectural features. Immunohistochemistry showing strong positivity for S-100 is requisite for diagnosis.^{7 8} Ancient schwannoma displays degenerative changes with relative loss of Antoni A areas and atypical nuclear features including hyperchromasia, multilobation but lacks mitotic figures.⁴ Cystic degeneration, calcification, xanthomatous change, interstitial hyalinisation and perivascular sclerosis are the other features.⁹

Most patients are asymptomatic at presentation. Pressure symptoms like dysphagia and dyspnoea occur due to compression of the lung and air way, oesophagus, right heart or even great veins on attainment of large size.¹⁰ Large mediastinal tumours are often first identified incidentally by plain radiographs as in our case and subsequent imaging with CT or MRI throw light on the underlying tumour. CT scan feature includes a sharply demarcated mass with low densities, mild enhancement and punctate calcification.¹¹ The best diagnostic tool is MRI showed hypodensity on T1-weighted images and hyperdensity on T2-weighted images.¹¹ Fine-needle aspiration or biopsy cannot provide a definitive histological diagnosis.¹² Hence, surgical resection is required to confirm the diagnosis. Surgical removal mitigates any pressure symptoms due to the tumour. Though the preferred surgical approach for resection is posterolateral thoracotomy for large posterior mediastinal tumours, we proceeded with a left posterior thoracotomy along the third intercostal space considering the size and the location of the tumour.¹² Smaller lesions free from vitals structures are suitable for video-assisted thoracic surgery.¹³ The combined neurosurgical and thoracic approach is ideal for tumour showing intraspinal extension (dumb-bell tumour).¹⁴ Surgical excision provides excellent survival. The tumour is benign and recurrence is uncommon.¹⁵ Malignant transformation of schwannomas is very rare.^{2 16}

Learning points.

• Ancient schwannoma of the posterior mediastinum is an extremely rare presentation.

• Ancient schwannoma should be borne in mind while evaluating posterior mediastinal masses in young patients.