Introduction

Solitary fibrous tumour is a rare neoplasm which can occur in a wide range of sites including mediastinum, peritoneum, retroperitoneum, nose and paranasal sinuses, thyroid, liver, orbit, parotid gland, breast, periosteum and soft tissues.

Intrapulmonary origin is extremely rare. We report a case of intrapulmonary solitary fibrous tumour, which radiologically was felt likely to represent a chest wall-based sarcoma.

Case Report

A 30-year-old previously fit and healthy man underwent a routine chest radiograph as part of a routine medical examination prior to diving lessons. He was a non-smoker with no family history of significance and with no history of prior exposure to asbestos. His chest radiograph showed a mass in the right lower zone. His physical examination was normal and he was asymptomatic. His routine blood investigations including full blood count, urea & creatinine and liver function tests were all normal. Subsequently, he underwent a computerized tomogram of the chest (CT) which demonstrated 7.5cm by 6 cm mass (Fig 1).

Figure 1

Figure 1: CT appearance of the mass mimicking chest wall-based tumour.

A CT-guided biopsy of the mass was inconclusive. The patient underwent limited thoracotomy. Surprisingly, at operation the mass was found not to be pleural based but was entirely intrapulmonary.

An intraoperative frozen section was performed which confirmed benign nature of the lesion and subsequently the mass was easily resected non-anatomically using a stapling gun. His post-operative course was unremarkable and he was subsequently discharged home after 4 days in the hospital. Macroscopically, the cut-surface of the mass was whorled, lobulated rubbery-firm and white in colour. Microscopically (Figs 2-4) there were bland spindle cells in a so-called ‘pattern less-pattern' separated by collagen. Immunohistochemical staining was diffusely positive for CD34 and bcl2 in tumour cells but negative for keratin.

Figure 2

Figure 2: Intrapulmonary tumour (top right) within congested lung (bottom left), H&E stain power *10.

Figure 3

Figure 3: Intrapulmonary tumour (right) separated from congested lung parenchyma (left) by an oedematous capsule (power *40). Staining with H&E.

Figure 4

Figure 4: The solitary fibrous tumour is composed of bland spindle cells separated by collagen resulting in a disorganized or so-called “pattern-less pattern”. Inset shows characteristic staining for CD34 in this SFT (power*400)

Coagulative necrosis was present but there were no features of malignancy i.e. low mitotic rate (less than 4 in high power field), no cytological pleomorphism or increased cellularity.

The diagnosis was benign intrapulmonary solitary fibrous tumour with a clear resection margin. The patient remains well 6 months later with no signs of recurrence.

Discussion

Solitary fibrous tumour (SFT) was first described by Klemperer and Rabin in 1931 as a form of mesothelioma arising from sub-pleural areolar tissue. Subsequently, Hernandez and Fernandez in early seventies proved the SFT are derived from the fibroblasts adjacent to the lining of the visceral pleura.

The aetiology of SFTs remains unknown. No association with asbestos exposure or with cigarette smoking or previous chest trauma has been established [₁]. Males and females are affected equally with no racial predilection ever been reported.

The peak incidence reported was in the 6th-7th decades but it tends to occur in all ages. The exact histogenesis of SFTs remains obscure. The current WHO (World Health Organization) definition is a localized tumour of parietal or visceral pleura, or peritoneum, consisting of spindled fibroblastic cells arranged haphazardly around an elaborate pericytoma-like vasculature. SFT tends to be negative for cytokeratin and muscle markers. CD34 is a useful marker for SFTs [₂,₃]. Bcl-2 has been reported to be highly sensitive marker of SFTs with a significant correlation between its expression and reduced tumour size [₁]. The vast majority of SFTs tend to arise from visceral pleura (80%) with 20% arising from parietal pleura [₄]. However, SFTs have been reported to arise in other sites including mediastinum, lung parenchyma, thyroid, liver, retroperitoneum, orbit, and paranasal sinuses [₂,₅]. SFTs occur in both benign and malignant forms. Reports suggest that the benign form tend to be firm, usually encapsulated and lobulated with a fibrous whorled appearance and occasional haemorrhage or necrosis on cut surface [₅,₆]. Some reports estimate that 12-23% fit the criteria of malignancy [₇]. Such criteria include high mitotic rate, nuclear pleomorphism, necrosis, infiltration of adjacent structures and poor circumscription [₄].

Most patients are asymptomatic on presentation with the diagnosis being suspected on plain chest radiography. In the symptomatic group, 1/3 of patients may present with chest pain, breathlessness or cough [₄,₆]. These symptoms may be related to the mass effect of the tumour. Hypoglycaemia is said to be present in 3% of cases and it may be related to IGF-2 [₄]. A small number of patients might develop pleural effusion or pneumothorax [₆]. The diagnosis can also be further characterized on CT or MRI scans but definitive diagnosis requires histology. The typical manifestation of SFTs on CT scan is that of a round or oval-shaped mass or nodule of a variable size [₇].

Surgery remains the only method of cure with the most important indicator of clinical outcome is complete resection with clear margins. It was reported that 1.4% of benign SFTs recurred after surgery [₄]. Open thoracotomies and Video-assisted thoracoscopic surgery (VATS) have been used [₁]. In the case of benign SFTs, no other modes of treatment are required once the resection is complete. The need for lobectomy or pneumonectomy is rare unless the mass had extensive adhesion to the lung and our case where the mass originated from the lung is an exception. However, long-term annual follow up with serial chest radiographs are recommended to detect recurrence.

In summary, benign intrapulmonary SFT is a rare tumour which can arise from a variety of sites. Surgical resection remains the main stay of treatment and periodic follow-up should be contemplated to detect early recurrence.

Correspondence to

Mr Nael Al-Sarraf M.R.C.S.I Registrar in cardiothoracic surgery. Department of cardiothoracic surgery, St James's Hospital, James's Street, Dublin 8, Ireland. Tel: 003531-4103389 Fax: 003531-4103700 E-mail: trinityq8@hotmail.com