Computed tomography and magnetic resonance imaging of a plexiform angiomyxoid myofibroblastic tumor: a case report
© The Author(s). 2017
Received: 22 July 2016
Accepted: 12 January 2017
Published: 19 January 2017
Plexiform angiomyxoid myofibroblastic tumor (PAMT) is a very rare mesenchymal tumor of the stomach. Here we report a case of pathologically confirmed PAMT with an unique cyst formation.
A 55-year-old male with a 10-year history of a gastric subepithelial tumor underwent computed tomography (CT) and magnetic resonance imaging (MRI). Two cysts were observed in the tumor, and the cyst wall showed moderately high intensity on T2-weighted images compared with the gastric wall. On dynamic study, the cyst wall showed a gradual enhancement pattern, and prominent enhancement was observed in the delayed phase. Laparoscopic partial gastric resection was performed, and a pathological diagnosis of PAMT was rendered.
We present a rare case of gastric PAMT, which was uniquely presented as cysts. One of the cysts in the tumor had an epithelial wall lining, which had never been reported before in gastric mesenchymal tumor, in addition to partial glandular structure. We reviewed our case, focusing on radiologic-pathologic correlation, and suggested hypothesis of cyst formation. According to our findings, PAMT with cyst formation would be included of differential diagnosis of gastric subepithelial tumors.
KeywordsStomach Mesenchymal tumor Magnetic resonance imaging Computed tomography
Plexiform angiomyxoid myofibroblastic tumor (PAMT) is a rare mesenchymal tumor of the stomach that was first described by Takahashi et al. in 2007 . The incidence of PAMT is estimated to be less than 1 in 150 compared with gastric gastrointestinal stromal tumor (GIST) , and only 34 cases of PAMT have been reported in the English language literature, with scant data pertaining to computed tomography (CT) and magnetic resonance imaging (MRI) findings [3–19]. Here, we describe a case of PAMT with unique cystic formation, focusing on the imaging findings and radiological-pathological correlation.
A 55-year-old male with a 10-year history of a gastric subepithelial tumor followed-up by upper gastrointestinal endoscopy at other clinic visited our institution with a complaint of tumor enlargement. The patient did not experience any discomfort, and his laboratory test results were all normal.
Upper gastrointestinal endoscopy showed a subepithelial mass, 2 cm in diameter, at the posterior wall of the gastric angle. Small dimples were observed at the apex of the tumor. A biopsy was performed, and viscous liquid was ejected from the tumor. The biopsy results were insufficient for a diagnosis.
The differential diagnosis of the gastric subepithelial tumor included schwannoma, GIST, ectopic pancreas, duplication cyst with cyst wall inflammation, and adenocarcinoma arising from a duplication cyst. Although the patient had a long history of a tumor, laparoscopic partial gastric resection was performed, because the possibility of malignancy could not be ruled out.
PAMT of the stomach is a rare mesenchymal tumor that typically shows a multinodular plexiform growth pattern. PAMT is composed of myofibroblastic spindle cells, separated by intercellular myxoid or fibromyxoid matrix, with rich arborizing capillaries . Immunohistochemically, PAMT is positive for vimentin and muscle actin . c-KIT, CD34, and S-100 protein is negative in PAMT, which are usually positive in GIST, GIST and solitary fibrous tumor, and schwannoma and neurofibroma, respectively. Typically, PAMT is positive for alpha-smooth muscle actin, and focal immunoreactivity for desmin and caldesmon is occasionally seen .
PAMT may also contain tumor cells with fibroblastic or smooth muscle characteristics [2, 4, 16] and therefore is sometimes reported as “plexiform fibromyxoma” or “plexiform angiomyxoid tumor” [2, 4]. However, Sing et al. suggested that PAMT could be distinguished from plexiform fibromyxoma according to its immunohistochemical and clinicopathological features . Those authors claimed that vascular invasion and extragastric extension are usually seen in plexiform fibromyxoma, with no immunoreactivity against caldesmon or desmin; in contrast, PAMT does not show vascular invasion, and focal reactivity for desmin and caldesmon is seen occasionally. Takahashi et al., who discovered PAMT, suggested that plexiform fibromyxoma is a fibroblastic trait of PAMT . Although the precise nomenclature remains controversial, “plexiform fibromyxoma” was classified as a mesenchymal tumor of the stomach in the 2010 World Health Organization classification of digestive system tumors . Because the majority of tumor cells show a predominantly myofibroblastic nature, we believe that PAMT is the appropriate diagnostic term reflecting the histogenesis and histology of this tumor. Furthermore, we believe that this is supported by the fact that more cases have been reported as PAMT, rather than as plexiform fibromyxoma, even after 2010.
To date, including the present case, 35 cases of PAMT have been reported in the English language literature. Of these cases, the patient age ranged from 7–75 years (median = 43 years), and no sex difference was evident (M:F = 17:18). Tumor size varied from 1.5 to 15 cm (mean 5.2 cm), and the majority of the PAMTs occurred in the gastric antrum and pylorus. However, PAMTs can occur anywhere in the stomach, including the fundus and body [7, 12, 15]. Since mucosal ulceration was seen in approximately half of the cases [1, 2, 4–6, 11, 12, 15, 17], PAMT may cause hematemesis, gastrointestinal bleeding, and anemia, although incidentally found PAMTs are not rare [9, 12, 15, 16]. Although vascular invasion was seen in some of the cases reported by Miettinen et al. , the prognosis of PAMT seems to be benign tumor, since no recurrence or metastasis has been reported to date.
Radiological feature of 6 cases of PAMT
Tumor size (cm)
Dynamic CT or MRI
Cyst formation appears to be rare in PAMT, and only three cases have been reported previously. In two of those cases, the tumor was continuous and showed a sac-like structure that had a hemorrhagic inner wall with multiple perforations [8, 14]. In the other case, hemorrhage, necrosis, and cystic degeneration were seen in a tumor 14 cm in size . Unlike these former cases, unique cyst formations were observed within the tumor in our case. Of the two cysts, the shrunken cyst did not show an epithelial wall lining, while the enlarged cyst did. We speculate that both cysts had an epithelial lining, but that the lining in the shrunken cyst was exfoliated. The cause of these cysts is unclear, and two explanations can be offered: the first is that the PAMT grew until it surrounded the heterotopic epithelial cells, and a cyst formed from the mucus secreted from these cells. This hypothesis may be supported by the fact that the tumor showed a partial glandular structure. The other explanation is that the PAMT occurred near these cysts and then grew until it surrounded them. Our case is the first report of a gastric subepithelial mesenchymal tumor containing a cyst with an epithelial lining; therefore, more data are required to confirm the true nature of these cysts.
In conclusion, we reported a case of PAMT, a rare subepithelial mesenchymal tumor of the stomach. MRI and dynamic study findings reflected the myxoid nature of this tumor well. A cyst with an epithelial wall lining was observed in the gastric subepithelial mesenchymal tumor for the first time. We believe radiologist should be aware that PAMT should be included to differential diagnosis of cystic subepithelial tumor with myxoid imaging feature.
Gastric gastrointestinal stromal tumor
Magnetic resonance imaging
Plexiform angiomyxoid myofibroblastic tumor
This case report was not founded by any grant or company.
Availability of data and material
The dataset supporting the conclusions of this article is included within the article.
HA performed the background literature review, drafted the manuscript and performed manuscript revisions. MS performed the surgery and manuscript revisions. YO performed histopathological specimen analysis, presentation and manuscript preparation. SK, YN, KY and KO assisted with image selection, image presentation, manuscript preparation and manuscript revisions. All the authors read the final paper version and approved it.
The authors declare that they have no competing interests.
Consent for publication
Written informed consent was obtained from the patient for publication of this case report and any accompanying images.
Ethics approval and consent to participate
Patient presented in this report was investigated within a retrospective study approved by the ethical review board of the Institute of Medical Science, University of Tokyo (Protocol ID Number 26-73-1126).
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