An extremely rare case of desmoplastic fibroblastoma was reported. Desmoplastic fibroblastoma should be considered in the differential diagnosis when desmoid-type fibromatosis in the chest wall is clinically suspected. Rim-like contrast enhancement at the periphery of the tumor with uniform thickness on gadolinium-enhanced T1-weighted MR images with fat suppression is the unique imaging feature in desmoplastic fibroblastoma that can distinguish it from desmoid-type fibromatosis preoperatively. However, when performing marginal excision of desmoplastic fibroblastoma in the chest wall only by diagnostic imaging before surgery, as in our case, it is necessary to consider the treatment strategy in case of desmoid-type fibromatosis as a result of pathological diagnosis.
Desmoplastic fibroblastoma is a unique form of benign, fibrous, soft tissue tumor [1,2,3,4]. These tumors have been observed at a wide range of anatomical sites, although they most commonly arise in the lower limbs and feet, the back, and the upper extremities, including the shoulder, upper arm and forearm, and hand [1,2,3,4]. The lesions typically infiltrate the adjacent fat and skeletal muscle tissues, although they rarely involve the bone [1,2,3]. Desmoplastic fibroblastoma in the chest wall is quite rare, with only seven cases having been reported in the literature [9,10,11,12,13,14,15]. These tumors have the potential to grow aggressively, and two cases have involved bone invasion [13, 15].
The following fibrous tumors should be considered in the differential diagnosis of tumors occurring in the infrascapular region: desmoplastic fibroblastoma, desmoid-type fibromatosis, solitary fibrous tumor, and elastofibroma dorsi [9]. Among these tumor types, some of the imaging features of desmoplastic fibroblastoma are also common characteristics of desmoid-type fibromatosis, also called desmoid tumor [3,4,5,6,7, 11]. CT scans typically reveal a well-defined inhomogeneous mass with a muscle-like density [13,14,15], without calcification or the presence of cystic lesions [3]. MRI demonstrates findings of low- to iso-intensity to muscle on T1-weighted images, low- to slightly high-intensity or mixed-intensity on T2-weighted images, and heterogeneous enhancement on gadolinium-enhanced T1-weighted images with fat suppression [5,6,7]. Ultrasound reveals mixed echogenicity [5, 6], and positron emission tomography reveals the diffuse uptake of fluorine-18 fluorodeoxyglucose [7].
An imaging feature that can distinguish desmoplastic fibroblastoma from desmoid-type fibromatosis is rim enhancement [16, 17], which is characterized as rim-like contrast enhancement at the periphery of the tumor, with uniform thickness on gadolinium-enhanced T1-weighted MR images with fat suppression [16]. Rim enhancement is considered to represent the abundant vascularity of the outer capsule-like fibrous tissue relative to that inside of the tumor [5, 16]. However, the clinical utility of rim enhancement as an imaging feature remains limited, as certain characteristics are not fully understood [5,6,7]. For example, the capsule-like structure is a thin fibrous tissue, which appears dark and exhibits less enhancement on gadolinium-enhanced T1-weighted MR images [5,6,7], and abundant vascularity has been found inside of, but not around, the tumor by Doppler ultrasound [5].
We consider that rim enhancement can represent an area of infiltrative growth with abundant vascularity. A recent study reported the characteristics of the cells of a patient with a tumor that grew invasively into the surrounding tissue, which were distributed compactly at its periphery, forming a gray-colored layer [3]. The inside of the layer was lined with regions of abundant vascularity, while the outside was encapsulated with thin fibrous tissue. This layer could be superimposed onto the region showing rim enhancement on gadolinium-enhanced T1-weighted MR images with fat suppression. A capsule-like structure can result in a smooth and clear margin. The signal intensity of rim enhancement may vary among individual tumors due to their cellularity and vascularity. To the best of our knowledge, in the English-language literature, there are no descriptions of the vascular distribution of desmoplastic fibroblastoma on dynamic contrast-enhanced CT. Therefore, further studies are necessary to confirm our hypothesis.
Patients diagnosed with desmoplastic fibroblastoma exhibit favorable surgical outcomes after marginal excision [3, 4], although the tumor may be misdiagnosed as desmoid-type fibromatosis and treated with a wide resection [3]. Therefore, the correct preoperative diagnosis of the type of tumor is important for preventing overtreatment that may result in a loss of function [3, 5]; however, this remains challenging, and the exact diagnosis depends on pathological and immunohistochemical analyses [3,4,5, 11, 18]. Therefore, a well-planned incisional biopsy preceding a definitive excision is recommended when a mass in the chest wall exceeds 5 cm in diameter [8].
As an alternative to conventional open surgery, video-assisted surgery has been proposed for the resection of chest wall tumors, as it allows for a reduced incision size and less tissue trauma [19]. In the present case, 5-mm 30-degree video-thoracoscopy was useful for visualizing the surgical margins in the deep tissue. The tumor size was obviously larger than the incision size; nevertheless, the resected specimen was easily extracted through the small incision due to its high elasticity. The minimally invasive surgery facilitated the accelerated recovery of this patient, who was experiencing shoulder pain caused by tumor compression. Marginal excision of the tumor with videoscopic assistance through a small incision may be an effective alternative approach for the treatment of desmoplastic fibroblastoma in the chest wall.
When performing marginal excision only by preoperative imaging examinations, as in our case, it is necessary to consider the treatment strategy in case of desmoid-type fibromatosis as a result of pathological diagnosis. Marginal excision has insufficient surgical margin to reduce the local recurrence of desmoid-type fibromatosis [20,21,22]. However, additional resection of the upper chest wall may damage important structures such as the brachial plexus and subclavian arteries and veins [20,21,22]. Therefore, postoperative adjuvant radiation therapy has recently been recommended as an alternative to additional resection [20,21,22]. With these in mind, we had prepared two scenarios: first, if the frozen section diagnosis was suspected to be desmoid-type fibromatosis, additional resection of infiltrated skeletal muscles would be performed through a large incision. Second, if the postoperative pathological diagnosis was desmoid-type fibromatosis, postoperative adjuvant radiation therapy would be performed.
The histopathological features of desmoplastic fibroblastoma include the presence of bland stellate or spindle-shaped fibroblasts, as well as myofibroblasts undergoing infrequent mitosis that are embedded within an abundant and dense collagenous matrix, with low to moderate vascularity [1,2,3,4, 11, 18]. Immunohistochemical testing is useful for confirming the histopathological diagnosis [4], with tumor cells that are diffusely positive for vimentin, focally positive or negative for α-smooth muscle actin, and preferably negative for other markers (4, 18).