MRI Findings of a Malignant Solitary Fibrous Tumor of the Diaphragmatic Pleura: a Case Report
INTRODUCTION
Solitary fibrous tumors (SFTs) are rare mesenchymal tumors that account for less than 2% of all soft-tissue tumors. SFTs occur in various anatomical sites (1-4); most tumors occur in the thoracic cavity, though rarely on the diaphragm (1, 2). Only 10- 20% of pleural SFTs are malignant (1, 4). Thus, there are rare reports on malignant SFTs of the diaphragmatic pleura in the literature. These tumors are often difficult to assess and characterize, either clinically or radiologically, because of their unusual locations (2).
Although multiplanar CT is usually the first-line modality for diagnosis, large tumors may be misdiagnosed as originating from the lung, liver, or retroperitoneal organs. MRI findings of SFTs have not been described in detail, because pleural tumors are usually not evaluated by using MRIs.
Here, we report a rare case of a malignant SFT of the diaphragmatic pleura in an elderly male patient, with a detailed description of the radiologic findings.
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Received: June 16, 2021 Revised: August 19, 2021 Accepted: September 7, 2021 Correspondence to:
Min Seon Kim, M.D.
Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, 88, Olympic-ro 43-gil, Songpa-gu, Seoul 05505, Korea.
Tel. +82-2-3010-1641 Fax. +82-2-476-0090 E-mail: 7endless7@naver.com
Copyright © 2021 Korean Society of Magnetic Resonance in Medicine (KSMRM)
Case Report
Solitary fibrous tumors (SFT) are rare mesenchymal tumors that most commonly develop in the pleura; they rarely involve the diaphragm. MRI has not been widely used to evaluate SFTs of the thoracic cavity, though it may be highly useful in assessing local invasion, predicting malignant potential, and helping in the differential diagnosis. However, MRI findings of malignant SFTs of the diaphragmatic pleura have been described in only two cases. We report a rare case of a malignant solitary fibrous tumor of the diaphragmatic pleura in an 82-year-old man. We describe the clinical and characteristic imaging features, including computed tomography, conventional MRI, and diffusion-weighted imaging. Contrast-enhanced MRI is more accurate than is CT in identifying the origin of SFTs, predicting whether they ae benign or malignant, and assessing local invasion. This imaging modality proved helpful in deciding on the treatment strategy for these rare tumors.Keywords: Malignant solitary fibrous tumor; Primary diaphragmatic tumor;
Computed tomography; Magnetic resonance imaging; Diffusion-weighted imaging Jeong Kyeom Kim1, Min Seon Kim2, Kyung Hee Lee1, Lucia Kim3
1Department of Radiology, Inha University Hospital, Inha University School of Medicine, Incheon, Korea
2Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
3Department of Pathology, Inha University Hospital, Inha University School of Medicine, Incheon, Korea
CASE REPORT
An 82-year-old man was transferred to our hospital with a chief complaint of right flank pain for two weeks. He also complained of dyspnea and had no history of trauma or underlying disease, except for hypertension. The physical examination revealed decreased lung sounds in the right lower chest at auscultation. His respiratory rate was 20 breaths/min, with an oxygen saturation of 89% measured by pulse oximetry. Other vital signs were within the normal range (body temperature, 36.9℃; pulse rate, 74 beats/min;
blood pressure, 126/67 mmHg). Arterial-blood gas analysis revealed mild hypoxemia with a partial pressure of oxygen (PO2) of 56.8 mmHg (normal range, 74-108 mmHg). Other routine blood counts and biochemical results were within the normal range.
Simple chest radiograph revealed much pleural effusion in the right hemithorax. We did a thoracotomy to drain the pleural effusion; approximately 3.8 L of straw-colored fluid were drained in five days. The fluid analysis revealed an exudate, and cytology was negative for malignancy.
Computed tomography (CT) (LightSpeed VCT; GE Healthcare, Milwaukee, WI, USA) using contrast medium (75 mL Iohexol, Bonorex 350, Central Medical Service, Seoul, Korea) showed residual pleural effusion and a large irregular mass in the right lower hemithorax, apparently descending and invading the retroperitoneum. On pre-contrast CT scan, the mass showed attenuation similar to that of the chest-
wall muscles, with central low-density areas of hemorrhage or cystic degeneration or necrosis (Fig. 1a). On contrast- enhanced CT scan, the peripheral solid portion of the mass showed heterogeneous enhancement; the central less- attenuated portion did not show enhancement (Fig. 1b).
The diaphragm appeared to deviate downward, although its central portion was barely distinguishable from the mass (Fig. 1c). CT had limitations in showing whether the origin of the tumor was the diaphragm or the pleura.
Therefore, our initial differential diagnosis included high- grade sarcoma originating in the diaphragm, SFT of the diaphragmatic pleura., or solitary metastasis with unknown primary origin. We also considered secondary involvement of the diaphragm from the retroperitoneal malignancy;
however, the probability was minimal, because the patient had no history of malignancy, and we detected no other primary cancer on abdominal and thoracic CT. Although the tumor invaded the right-side retroperitoneum, we thought it was located within the thoracic cavity rather than in the abdominal cavity. We used contrast-enhanced MRI (Signa Architect 3.0T; GE Healthcare, Milwaukee, WI, USA) using Gd-DOTA (Dotarem, Guerbet, Aulnay-sous-Bois, France) to further characterize the mass and evaluate its exact origin and extent. The MRI showed an irregular mass of 8.5 × 6.1 × 8.4 cm in the right lower hemithorax. The solid portion showed iso- to hypo-intensity relative to the adjacent chest-wall muscle on T2-weighted images (Fig. 2a, Fig. 3a), and we observed intermediate signal intensity on
Fig. 1. Non-contrast-enhanced axial CT images (a) show a large, heterogeneous mass (arrow) with a central hemorrhagic component on the right hemithorax base. The attenuation of the mass is similar to that of the adjacent chest-wall muscles.
Contrast-enhanced axial (b) and coronal (c) CT images show an irregular mass (white arrows) measuring 8.5 × 6.1 × 8.4 cm with strong heterogeneous enhancement. The mass might have crossed the right diaphragm (black arrow); however, CT is limited in precisely defining the invasion of surrounding areas.
a b c
T1-weighted images (Fig. 2b). Coronal MR images clearly showed the right hemidiaphragm. The mass laid on the diaphragmatic pleural surface and was connected to it with a broad base (Fig. 3a, b). The peripheral solid portion of the tumor showed heterogeneous signal intensity with poorly enhancing areas on gadolinium-enhanced T1-weighted images (Fig. 2c). An SFT was suspected, because the mass appeared to originate from the diaphragmatic pleura and was iso- to hypointense on T2-weighted imaging (Fig. 2d), which may be correlated with the fibrous component of the tumor. The tumor directly invaded the right diaphragm with a concave depression, extending beyond the diaphragmatic muscle into the retroperitoneal cavity, laterally displacing the right kidney (Fig. 2d). On MRI, the central portion of the tumor showed high signal intensity on T2-weighted images and low signal intensity on T1-weighted images (Fig. 2a, b), as can be seen in hemorrhage. In addition, it infiltrated the
adjacent right proximal psoas muscle at the level of the L1 vertebral body. The soft-tissue contrast in MRI was better than that in CT scan images of the same part (Fig. 3c). We obtained DWI using b values of 50, 500, and 800 s/mm2. The apparent diffusion coefficient (ADC) distribution was demonstrated on an ADC map from the DWI data using a standard workstation (Signa Architect, GE Healthcare, Milwaukee, WI, USA). The peripheral solid portion showed high signal intensity on high b-value DWI (b = 800 s/mm2) and low signal intensity on ADC maps (Fig. 4a, b). The average ADC value measured in the low-signal-intensity portion of the ADC map was 9.9 × 10-3 mm2/s, and the maximum value was 10.0 × 10-3 mm2/s. Thus, we suspected malignant transformation of the SFT. We did an ultrasound-guided percutaneous biopsy for surgical planning to exclude metastasis or other unresectable malignancy, and confirmed the diagnosis of SFT. There was no evidence of distant metastasis in thoracic
Fig. 2. The MR axial T2-weighted image (a) shows a heterogeneously intermediate-to-low signal intensity mass (arrow) in the right lower hemithorax. The area that appeared to be a hemorrhage in the tumor showed high signal intensity on T2-weighted images and low signal intensity on T1-weighted images (a, b). Axial T1-weighted images (b) and post-contrast axial T1-weighted fat-suppressed images (c) show a heterogeneously enhancing lobulated mass (arrows) with multifocal hypointense areas that enhance poorly. The multifocal areas with low signal intensity on both T1- and T2-weighted images indicate the fibrous component of the tumor. In addition, MR images clearly show an extension of the mass into the retroperitoneal space (arrows) and infiltration of the right proximal psoas muscle beyond the diaphragm on a fat suppression T2-weighted image (d). The right kidney is deviated to the right side.
d
a b c
and abdominal CT; we did not do PET-CT. We decided on a complete resection.
On traditional thoracotomy with an incision in the eleventh-twelfth intercostal space, we found that the tumor
originated from the diaphragmatic pleura. The mass was directly invading the right diaphragm and retroperitoneal cavity. We excised the intrathoracic adhesions; however, the tumor was not completely removed, because of severe Fig. 3. The coronal T2-weighted images (a) show a heterogeneously intermediate-to-low signal intensity mass (black arrows) on the right hemithorax base. The mass has a broad base of attachment on the diaphragmatic pleura (arrows) (b). The tumor has invaded the right diaphragm (arrows), as seen in the coronal images (b). When the same area was scanned in the coronal image of the contrast- enhanced CT and the T2-weighted coronal image, the contrast of the soft tissue (arrows) was superior in the MRI (c).
a b
c
Fig. 4. DWI at b factor 800 s/mm2 (a) and ADC map (b). DWI shows high intensity (arrow) with a high b value and reduced ADC values (arrow), representing significantly restricted diffusion.
a b
retroperitoneal adhesion. The cut surface of the tumor showed a pale-grayish, lobulated, fibrous mass with multifocal yellow necrotic portions and a central brownish tan area, seemingly hemorrhagic (Fig. 5a). Histopathological
evaluation revealed a spindle-cell tumor with multifocal necrosis, and the tumor cells had high cellularity and high mitotic activity (5-10 per 10 high power fields) (Fig.
5b, c). On immunohistochemical staining, the specimen
a b
c d
Fig. 5. The cut surface of the tumor shows a pale grayish, lobulated fibrous mass with multifocal yellowish necrotic portions and a central brownish tan area, seemingly hemorrhagic (a). The microphotographs (× 40 and × 100, Hematoxylin & Eosin stain) show that the tumor was composed of spindle cells and had high cellularity and high mitotic activity (b, c). Immunohistochemically, the specimen was positive for CD34 (d) and focally positive for STAT6 (e).
e
was positive for CD34 and focally positive for STAT6 and cytokeratin. The final histopathological diagnosis was malignant SFT (Fig. 5d, e). The patient underwent postoperative adjuvant chemotherapy and radiation therapy, because we could not do complete resection of the tumor, and was regularly followed up without tumor recurrence for ten months.
DISCUSSION
SFT of the pleura is a mesenchymal neoplasm of fibroblastic or myofibroblastic origin. This type of tumor was first described in the pleura, though it can occur in other regions, including the head, neck, breast, abdomen, pelvis, and extremities (1). SFTs account for only 5% of all tumors arising from the pleura (1); only a small fraction of the pleural SFTs originates from the diaphragmatic pleura, and the incidence is unknown (2).
Although most SFTs of the pleura have are benign, approximately 10-20% are locally aggressive or malignant (1-4). In particular, SFTs originating from the diaphragmatic pleura have a higher malignancy rate than do those from different anatomical locations (3). The behavior of these tumors is often unpredictable and sometimes uncorrelated with the histological findings. A biopsy alone cannot distinguish between benign, locally invasive, or malignant forms (4). Predicting the tumor biology before surgery is crucial in selecting candidates for adjuvant chemotherapy and planning surgical procedures. CT imaging features suggestive of malignancy include a size > 10 cm, interval increase in size, infiltration into adjacent soft tissues and chest-wall invasion, extensive necrosis and hemorrhage (attenuation heterogeneity), ipsilateral pleural effusion, and growth beneath the parietal pleura of the chest wall, diaphragm, or mediastinum (3, 5). SFTs are commonly considered to have a distinct MRI appearance, consistent regardless of the anatomical region of origin (1). SFTs are hypocellular fibrous tumors that tend to have lower signal intensity on T2-weighted images than do tumors with high cellularity or that contain more extracellular myxoid matrix (1, 4). These areas of fibrous tissue do not enhance well (1). However, SFTs can show different signal intensities on T2-weighted MR images, depending on the proportion of spindle cells, fibrous stroma, and vascular tissue (6).
Because of the rarity of malignant SFTs, information on their MR features is sparse. The conventional MR features of malignant SFTs on MRI are generally nonspecific
and insufficient for pathognomonic diagnosis (7). MRI sometimes depicts intratumoral flow voids in large SFTs, though these findings are not correlated with malignant potential (7). Large solitary fibrous tumors may have intermixed areas of cystic degeneration, hemorrhage, and necrosis (1). These changes of SFTs can appear as heterogeneous geographic enhancement on CT and high signal intensity on T2-weighted images (1).
Few DWI features of malignant SFTs of the diaphragm were given in previous reports. According to a previous study, the mean ADC value for the 12 benign SFTs for which measurements could be obtained was 1.27 mm2/s (range, 0.90-2.20 mm2/s) regardless of histologic type and location (6). In a recent study of soft-tissue tumors, mean ADC on a 6-mm coarse filter was an independent factor that strongly suggested malignancy with a single MR feature on 3T MRI (8). In our patient, the tumor showed a significantly lower ADC value (9.9 × 10-3 mm2/s), corresponding to the previous report by Inaoka et al. (9). We suspected malignant transformation of this tumor from CT findings, because of the tumor size, heterogeneity, presence of pleural effusion, and local invasion. However, if these ancillary findings are not present, the radiological differentiation between a benign and a malignant neoplasm remains difficult.
Although further studies of many more malignant SFTs are necessary to establish the mean ADC value of these tumors, DWI and ADC maps may be helpful for predicting the malignancy potential.
Tumors of the diaphragmatic pleura are rare lesions, often difficult to distinguish from diaphragmatic, pleural, pulmonary, or extra-thoracic tumors (2). The first step for the differential diagnosis is to discover the origin of the tumor. A pleural lesion will be joined to the pleural surface at an obtuse angle and attached by a broad base.
In contrast, a diaphragmatic lesion will be centered in the diaphragm. In our patient, the CT could not well define the origin of the tumor, because the diaphragm was barely distinguishable from the mass. Although the tumor extended into the retroperitoneum, the diaphragm was relatively well preserved on the coronal MRI. Also, the tumor seemed to have a broad base on the diaphragm. At the time, our MRI protocol did not include a real-time sequence, CINE, which is often used to evaluate lesion movements during the different respiratory phases in the chest (10). This sequence can be helpful in examining the diaphragm or evaluating the adherence of a lesion to a soft-tissue organ or adjacent surface (9). Another useful typical imaging feature of SFTs is the presence of large collateral feeding vessels; however,
these vessels were not visible in our patient (10).
According to Lococo et al. (5), the factor that most affects the long-term survival of patients with malignant SFTs is a complete surgical resection. In addition, invasion of the chest wall also affects the prognosis (5). Therefore, an accurate preoperative assessment is critical for the surgeon to decide on the surgical method and range.
As demonstrated in our case, MRI is superior to CT for evaluating the tumor origin, extension, and local invasion, because of its higher soft-tissue contrast (1, 4).
In summary, we present the use of MRI for the imaging of a malignant diaphragmatic SFT arising from the pleura.
In addition, MRI should be highly useful in identifying invasiveness, predicting the malignant potential, and aiding the differential diagnosis of diaphragmatic tumors.
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