Massive Solitary Fibrous Tumor (SFT) of the infratemporal and pterygomaxillary fossa treated by combined endoscopic approach

Introduction

Solitary fibrous tumors (SFTs) were first described by Klempere and Rabin⁷ in 1931 as spindle-cell tumors originating from the pleura. Until recently, there was some debate with regards to the name and origin of these tumors¹¹. The term haemangiopericytomas (HPCs) was used by Stout and Murray¹⁰ in 1942 when they described a type of vascular tumor derived from the capillary pericytes, previously described by Zimmermann in 1923.

However, over the years, the use of the term HPC has raised many issues. Morphological, immunohistochemical and clinical features of HPCs are not specific for one entity^3,8. With the exception of myopericytoma, infantile myofibromatosis and HPC-like lesions of the sinonasal tract showing myoid differentiation, all other HPC-like lesions are best considered as subtypes of SFT³. Due to their mesenchymal origin⁵, we now are aware that SFTs may involve several extrapleural sites including soft tissues or meninges^5,8.

Only a few cases of SFT have been described in the literature involving the skull base^9,14, but a massive malignant SFT of the soft tissue involving the infratemporal and the pterygomaxillary fossa is extremely rare and represents a multidisciplinary clinical and surgical challenge. The vast extent of the tumor and its localisation near vital structures makes it an important challenge for the surgical team, especially when the tumor shows malignant histological characteristics. Classical transfacial surgical approaches may leave unsightly scars with high morbidity. However, a combined approach with nasoendoscopy provides excellent access for tumor resection without any concerns over the aesthetic result.

To our knowledge, this is the first case reported of a massive SFT involving this region, treated with minimal invasive surgery without any facial osteotomies.

Case report

Written informed consent for publication of clinical details and clinical images was obtained from the patient.

Examination

The clinical examination revealed subtle proptosis of the right eye. Using flexible nasolaryngoscopy, we saw small bulging in the nasal cavity on the right side. All cranial nerves were intact and no lymph node enlargement was found. The patient was not complaining of epistaxis or nasal obstruction.

The first computer tomography scan with intravenous iodine contrast, requested by the ophthalmologist, indicated a lesion in the right pterygomaxillary fossa eroding the base of the skull to the temporal lobe and to the right cavernous sinus. There was also an extension in the orbital apex and erosion of the pterygoid process with bulging of the posterior wall of the right nostril. The mass was visible with contrast gadolinium enhancement on the MRI. Its dimensions were 4.6cm anterioposterior × 3.3cm transverse × 4.7cm cranio-caudal (Figure 1–Figure 3).

Figure 1. Preoperative computed tomography of right pterygomaxillary fossa solitary fibrous tumor showing compression of the right optic nerve.

Figure 2. Magnetic resonance scan of the rhinopharynx - Global homogeneous enhancement with gadolinium of the mass.

Figure 3. Magnetic resonance scan of the rhinopharynx postoperatively showing subtotal removal of the tumor.

Shortly after the MRI, a transmaxillary endoscopic biopsy was performed. The result of the frozen tissue examination was compatible with a diagnosis of neuroendocrine carcinoma or hemangiopericytoma. The final pathology indicated a solitary fibrous tumor and this was confirmed by an expert otolaryngologist pathologist in Toronto. There was hypercellularity and a mitotic index of 4 mitoses per field, a sign of a highly aggressive tumor⁸ (Figure 4).

Figure 4. A, B: Haematoxylin and eosin stain exhibiting a dense arrangement of polygonal cells with highly cellular patternless sheets with branching vascular pattern, thickened endothelial spindle cells with protuberant nuclei, C: CD34 staining consistent with SFT diagnosis, D: Bcl-2 staining intensely positive at magnification 20×.

Discussion

SFTs are rare spindle-cell neoplasms of variable histological grades. Despite some confusion in the past regarding HPC and SFT, the relationship between the two is now more obvious. It is also known that SFT of the soft tissue can occur in the head and neck region and throughout the body^4,6,12.

Most cases of soft tissue SFTs occur in the early fifth decade of life⁸ with no sex predilection^2,3. Its occurrence is less than 2% of all soft tissue tumors⁸.

Skull base SFTs may include a wide variety of symptoms, although they are usually asymptomatic on presentation¹³. The symptoms manifest most frequently as a slowly expanding painless mass. Decreased vision, nasal obstruction, local pain, recurrent sinusitis, epistaxis, headaches, dural erosion, cerebrospinal fluid rhinorrhea, anosmia and lower cranial nerve palsies may all be part of the patient symptomatology.

SFTs from any site are usually benign and surgical resection alone is curative^4,11. However, malignancy is possible, although the criteria remain imprecise. It may be suspected with the radiology exam (mass >10cm) or by the presence of metastasis¹³. The presence of infiltrative margins with surrounding tissues, high mitotic count (≥4 mitoses per 10 high-power high fields) of cellular pleomorphism and tumor necrosis also suggests malignancy^4,8.

The main treatment is surgical for benign and malignant SFTs. There is little evidence (principally from case reports) from adjuvant radiotherapy and none supporting the use of chemotherapy. But when histopathology suggests malignancy or when there are positive surgical resection margins, radiotherapy must be discussed, as for other sarcomas^1,8.

In conclusion, we successfully managed a case of massive solitary fibrous tumor of the soft tissue, involving the infratemporal and pterygomaxillary fossa. With the combination of conventional frontotemporal craniotomy with sinus surgery endoscopy, we were capable of removing most of the tumor while preserving vital structures close to the tumor and without the need for facial osteotomies, leaving the patient without any undesirable scars. With the addition of adjuvant radiotherapy treatment, we were able to achieve no sign of recurrence at the one-year follow-up.

SFT is very uncommon but should be part of the differential diagnosis in patients with a skull base lesion. Diagnosis is difficult but pathologists should be aware of the classical finding of this disease consisting of spindled cells in a disorganized pattern, with alternating hypocellular and hypercellular areas separated by hyalinized collagen and branching HPC-like vessels. Also the immunophenotyping staining positive for the presence of CD34 and Bcl-2 can be useful. The surgical approach needs to weigh risks and benefits of subtotal vs. total resection because of the surrounding vital structures.