Solitary fibrous tumour of the parapharyngeal space

We report a case of a 56-year-old male who presents with a progressive, dull, aching pain in the throat for 1 year’s duration and foreign body sensation on the left oropharyngeal region. On clinical examination he had a prominent left oropharyngeal submucosal bulge with no abnormalities of the overlying mucosa.

The CT scan (axial section, figure 1) reveals the presence of a well-defined, lobulated mass located in the left pre-styloid parapharyngeal space (PPS), impinging upon the oropharyngeal airway, which is displaced to the right side at the level of the palatine tonsil. An MRI was performed for better soft tissue characterization. On T2W images (coronal plane, figure 2), the mass shows low signal intensity, with scattered linear hyperintensities, creating a distinctive black-and-white striped pattern. This unique appearance is further emphasized on contrast-enhanced fat-suppressed T1W images (coronal plane, figure 3), where the mass displays heterogeneous enhancement, resembling a “chocolate-chip cookie”. This lobulated mass shows discrete borders, does not infiltrate neighbouring structures, and reduces the transverse diameter of the oropharyngeal airway.

The patient underwent surgical resection via a transoral approach, and a complete removal with negative margins was successfully accomplished, and the patient recovered uneventfully. Pathology disclosed a solitary fibrous tumour.

Lesions of the pre-styloid PPS are uncommon. Most often, this space is displaced or infiltrated by lesions originating in neighbouring spaces, namely the mucosal pharyngeal space, masticator space and the parotid space, due to its close relationship with the deep lobe of the parotid gland. Once the lesion can be assigned to the PPS, there is a limited list of differential diagnoses, including mesenchymal, minor salivary glands and lymphoid tumours, metastases and rare benign cysts. The most common lesions of the PPS are minor salivary gland tumours, particularly pleomorphic adenoma and neurogenic tumours. Lipomas and vascular malformations are easily recognized by their distinctive imaging features. Among soft tissue sarcomas, rhabdomyosarcomas and malignant fibrous histiocytomas affect predominantly the pediatric age group [1,2].

Solitary Fibrous Tumors (SFTs) are mesenchymal spindle cell neoplasms, only rarely reported in the PPS. Most often seen in serosal surfaces, particularly the pleura, the head and neck region is their second most common location. In order of decreasing frequency, they affect the sinonasal tract, the orbit, the oral cavity, salivary glands and neck. Presenting symptoms depend on location but most often include an indolent, painless, palpable mass [3–5].

Although imaging findings are non-specific, a few radiological features may suggest this diagnosis. The distinctive “chocolate-chip cookie” appearance on post-contrast CT and MR images, the presence of spontaneous hyperdense areas on CT and the stripped black-and-white pattern on T2W MR images. This heterogeneity is linked to collagen content (low T2 signal intensity) and the presence of areas of myxoid degeneration, characterized by lower cellularity (high T2 signal intensity). Occasionally, intratumoral flow voids can be observed on MRI. Suspicion of malignancy increases when locally invasive features such as bone, vascular invasion, or perineural spread are present, as well as when hypermetabolism is detected on FDG-PET-CT scans [6–8].

The preferred treatment is complete surgical resection with negative margins, the best predictor of the likelihood of local recurrence. In cases where achieving clear surgical margins is challenging, adjuvant radiotherapy is often recommended. There is also evidence that antiangiogenic treatment is effective for unresectable disease. Due to their potential for recurrence, radiological follow-up after surgery is recommended for SFTs, particularly those with aggressive histologic features and/or positive margins. These cases have a higher tendency to recur and warrant closer monitoring [8–10].