Reactive Nodular Fibrous Pseudotumor Mimicking Metastatic Tumor After Gastric Cancer Operation: A Case Report and Literature Review

Abstract

We describe a case of reactive nodular fibrous pseudotumor (RNFP) misdiagnosed as lymph node metastasis after gastric cancer surgery. Additionally, we summarize the clinical and imaging characteristics of RNFP, combined with the literature, to improve the understanding of preoperative diagnosis. Radiological features of RNFP are a homogenous, isodense, solid mass with gradually mild enhancement on multiphasic abdominal computed tomography (CT), and slight ¹⁸F-FDG uptake by positron emission tomography/computed tomography (PET/CT). To the best of our knowledge, this is the first report in the English literature of a case of reactive nodular fibrous pseudotumor associated with gastric cancer and its appearance on PET/CT images.

Introduction

Reactive nodular fibrous pseudotumor (RNFP), which is described as a rare benign tumor−like lesion, was first reported by Yantiss et al. in 2003 (1). RNFP is related to a history of abdominal surgery, injury, or inflammation, and lesions occurring after surgery for abdominal malignancy are easily misdiagnosed as tumor recurrence/metastasis. We analyzed a case of RNFP misdiagnosed as lymph node metastasis after surgery for gastric cancer and reviewed the relevant literature, with the aim of summarizing its clinical and imaging features and improving the understanding of the lesion.

Case Presentation

In July 2018, a 54-year-old male patient with latent abdominal pain, and confirmed gastric malignant tumors by endoscopic biopsy, underwent laparoscopic radical distal gastrectomy (Billroth II gastrointestinal reconstruction) in our hospital. The postoperative pathological diagnosis was early gastric cancer with moderately to poorly differentiated adenocarcinoma in the gastric antrum, superficial bulge type (type IIa). The tumor was limited to the lamina propria.

One year later, a CT scan of the abdomen revealed a round-like mass with a diameter of 5.0 cm near the anastomosis in this patient, with well-defined isodensity and no necrosis. The lesion showed slight enhancement, and the CT values of the non-contrast, arterial, and venous phases were 32HU, 43HU, and 49HU, respectively (Figures 1A–C). Moreover, ¹⁸F-FDG PET/CT (Siemens Biograph 64) was performed 60 min after intravenous injection of 310.8 MBq (8.4 mCi) of 18F-FDG. ¹⁸F-FDG PET/CT images revealed a minimally increased FDG uptake with SUVmax of 3.6 for a solid mass in the operative area of gastric cancer with a relatively clear boundary (Figure 2). Gastrofiberscopy showed residual gastritis and anastomotic stomatitis, with no sign of a tumor. Based on laboratory tests, the carcinoembryonic antigen level of the patient was slightly increased (5.1 ng/ml, normal range 0–5).

Figure 1

Figure 2

A retrospective review of previous postsurgical scans revealed a nodule with a diameter of approximately 1.0 cm (Figures 1D–F). Given the apparent growth of the lesion and the history of gastric cancer, lymph node metastasis was suspected, and laparoscopic splenectomy and splenic hilar lymph node dissection were performed. During the surgery, a 5.0 cm × 5.5 cm light-red mass with medium texture and clear boundaries was detected in the splenogastric space near the tail of the pancreas by laparoscopy (Figure 3A). The tumor was closely adhered to the spleen artery and back wall of the gastrointestinal anastomosis. Lesions on the cut section were grayish white. According to microscopic pathology, the proliferative spindle cells were disorderly arranged, with a small amount of interstitial lymphocyte infiltration. An expression of vimentin and smooth muscle actin (SMA) in most spindle cells was observed by immunohistochemical analysis, but there was no staining for S100 proteins, CD117 (c-kit), DOG1, P63, CK(Pan), or anaplastic lymphoma kinase (ALK-1 A4). The final diagnosis was reactive nodular fibrous pseudotumor (Figure 3B). Surgical excision was complete, and no evidence of disease was found 28 months later.

Figure 3

Discussion

RNFP is considered to be a reactive benign lesion associated with previous surgical procedures or inflammatory disorders. Since 2013, twenty-seven cases of RNFP have been reported (Table 1) (1–16), involving 16 males and 11 females, with ages ranging from 1 day to 72 years of age; the mean age was 47 years of age. Eight of these patients had a history of abdominal surgery for abdominal trauma, acute abdomen, cholecystitis, gastric stromal tumor, or colon cancer, although no lesions following a diagnosis of gastric cancer have been reported. Of the 27 cases, 12 have single lesions, and the other 15 cases involved multiple lesions. Locations were as follows: the colon or appendix (8 cases), the small bowel (7 cases), the mesentery and omentum (7 cases), the gastric wall (2 cases), and the hepatic capsule, ovary, or peripancreas (1 case each).

Microscopic examination of RNFP reveals proliferation of stellate or spindle cells with a keloid-like appearance in a dense collagenous background, accompanied by infiltration of lymphocytes and plasma cells. Immunohistochemistry shows positive staining for vimentin and smooth muscle actin and negative staining for CD34 and S-100. The immunohistochemical characteristics of the present case are consistent with previous results (10).

Of the cases reported thus far, only 4 had CT and/or MR images. Combined with our case and the literature (6, 11, 12, 16), the imaging features are as follows. On plain CT, the lesion is isodense, with progressively mild enhancement observed on postcontrast CT. MR manifestations are related to the content of fibroblasts in the RNFP. In general, the lesion shows homogenous hypointensity on T1WI and a mixed high-signal shadow with a slightly hypointensity area on T2WI. Enhancement mode results are the same as those by CT. If the lesion is rich in fibroblastic components, the appearance of a markedly low signal on T2WI has certain characteristics. There is no PET/CT description of RNFP in the literature. In the present case, PET/CT images showed a round-like mass with slightly increased FDG metabolism. The features of isodensity and progressively mild enhancement on CT images corresponded with the literature.

RNFP should be differentiated from lymph node metastasis related to gastric cancer and extragastrointestinal stromal tumors (EGIST). Enlarged lymph nodes are irregular in shape, with marginal lobulation or spiny processes. Uneven high enhancement with central necrosis and ring enhancement when the diameter of the node is more than 10 mm are typical; PET/CT FDG metabolism is significantly increased. Another neoplastic entity to consider in differential diagnosis is an EGIST, which is commonly a unique large mass with a round or irregular shape and uneven density. Cystoid degeneration and necrosis are common. EGIST exhibits significant enhancement during the arterial phase due to the hypervasculature present, in contrast to the mild enhancement of RNFP.

Surgical resection is currently an effective treatment for RNFP. No cases of RNFP recurrence or metastasis have been reported to date.

Conclusion

RNFP is rare and may be related to postoperative fibroinflammation. We report for the first time a reactive nodular fibrous pseudotumor associated with surgery for gastric cancer and its appearance on PET/CT images. Awareness of the imaging features of RNFP is important for its diagnosis. For patients who have been treated with surgery for abdominal malignant tumor, to avoid misdiagnosis and overtreatment, the possibility of RNFP should be considered if the mass is found to have the above imaging findings.

Funding

This research was supported by the Zhejiang Provincial Natural Science Foundation of China (Nos. LGC22H180002, GC20H180003 and Y21H160246) and Zhejiang Medical and Health Science and Technology Project (Nos. 2020KY406, 2021KY508).

Publisher’s Note

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