Solitary Fibrous Tumor of the Pleura

(aka Benign Mesothelioma, Localized Mesothelioma)

Epidemiology

Account for 8% of all benign tumors in the chest (making them more rare than mesothelioma)
Account for 10% of all primary pleural neoplasms
Median Age of Presentation: 57 y/o
No epidemiologic relationship to asbestos exposure

Etiology

Physiology

Probably originates from pleuripotential fibroblasts (rather than from mesothelial cells, like mesothelioma)

Pathology

-Origin: 66% are from visceral pleura and 33% are from parietal pleura
-Location: in cases where they appear within the lung parenchyma, they are attached to pleura via a pedicle or stalk
-May occasionally arise in a fissure
-Focal areas of malignant cells: seen in 20% of cases

-Macroscopic: whirled appearance with central necrosis, hemorrhage, and calcification
-Microscopic: elongated, spindle-shaped cells
–Stains positive for vimentin and CD34 and negative for keratin (these stains help distinguish it from mesothelioma)

Diagnosis

– FOB:

CXR/Chest CT Pattern:
-Location: usually pleural in location
–In cases where they appear within the lung parenchyma, they are attached to pleura via a pedicle or stalk
-Character: solitary, circumscribed, homogeneous, round and firm with clear borders (with no evidence of invasion into adjacent structures)
–Average size: 6 cm (although it may rarely occupy the entire hemithorax)
-Appearance: they uniquely form an acute angle with chest wall (this is unusual for pleural-based masses and may be due to their size and ability to hang from a pedicle into the lung)
-Calcification: dense calcification may be seen occasionally
-Mobility: mass may be mobile on its pedicle (seen with decubitus views)
-Heterogenous enhancement: corresponds with areas of vascularity
-Low attenuation areas: corresponds to areas of cystic necrosis or hemorrhage
-Presence of pleural effusion: does not alter the prognosis

Chest MRI: low signal on T1 (83% of cases) and T2 images is consistent with a fibrous tumor, but does not provide any diagnostic or prognostic information

PET: solitary fibrous tumors have low or absent uptake

FNA: may be unhelpful, as the malignant areas can be missed due to sampling problems (only 20% have focal malignant areas)

Clinical

Symptoms/Signs: >50% of cases are asymptomatic (in those with symptoms, symptoms are usually chronic)
-80-90% behave in a benign manner (remaining 10-20% behave in a malignant manner)

1) Dyspnea:
2) Chest wall pain:
3) Cough:
4) Fever: seen in some cases
5) Paraneoplastic syndromes:
a) Hypertrophic osteoarthropathy (14-19% of cases):
-Higher incidence (up to 90% of cases) with tumors >7 cm in size
-Usually resolves over few months after tumor resection
b) Hypoglycemia (4-14% of cases): due to IGF-II secretion by tumor
-These are usually >10 cm tumors
-Responds to tumor resection
-Steroids can be used in the interim, as they suppress IGF-II secretion

Treatment

Surgical Resection: main diagnostic and therapeutic modality
-En bloc resection with a 1-2 cm margin is curative in most cases
-Wedge resection of lobectomy may be used for tumors arising from visceral pleura

Recurrence:
-Presence of malignant elements in tumor is associated with local recurrence and worse metastasis-free survival
-Recurrences have been documented up to 17 years after resection (sometimes with malignant transformation)
-Recurrences should be screened for with annual imaging
-Recurrences may be heralded by return of the paraneoplastic syndrome

Prognosis

Excellent chance for cure with surgical resection

MD Nexus