Desmoid-type fibromatosis (DF) is a rare locally aggressive soft tissue tumor that can arise in any part of the body. Intra-abdominal localization is the least common; its clinical presentation is variable and depends chiefly on tumor site. Most patients present with asymptomatic masses; however, presence of acute symptoms, albeit uncommon, often warrants indication for surgical treatment [1],[2],[3],[4]. In this report we describe two cases of intra-abdominal DF presenting as acute abdomen, which underwent surgical resection between February and March 2020, highlighting their presentation, pathologic features, diagnostic workup, and surgical management.

Case 1

A 55-year-old man with a recent history of dyspepsia, epigastric pain, and occasional episodes of bowel-obstruction presented to our clinic due to a diagnosis of an abdominal mass. No suspected symptoms of COVID-19 were confirmed by negative thorax computed tomography (CT) scan and negative nucleic acid amplification test (NAAT) for SARS-CoV-2.

Physical examination and laboratory tests were negative. Colonoscopy showed complete obstruction of the hepatic flexure, ascribed to extrinsic compression. Abdominal CT showed a 9.6 cm solid, oval mass located in the mesentery, imprinting on the surrounding intestinal loops without full-blown infiltrative signs (Figure 1). This lesion could be traced back to the desmoid tumor in the first hypothesis, without being able to exclude other diagnostic hypotheses. Biopsy results were compatible with desmoid fibromatosis. No family history of fibromatoses or familial adenomatous polyposis (FAP) was reported; however, the patient had history of abdominal trauma.

A laparoscopy was performed which confirmed the voluminous solid oval mass, starting from the mesentery seemingly infiltrating an ileal loop and the transverse colon (Figure 2). Due to difficulty to isolate and identify the correct intestinal structures involved, an open laparotomy with en bloc resection of the mass, ileal loop, and colonic segment was performed (Figure 3) and two mechanical side-to-side anastomoses were carried out (ileo-ileal and colo-colonic).

Gross inspection of the surgical specimen showed a capsulated mass (measuring 12 × 11 × 7 cm) tightly adherent to the resected intestinal loops length about 75 cm; cut surface was firm and glistening white, with fasciculated appearance. Upon macroscopical examination, surgical margins were free of tumor. Histologic examination demonstrated a proliferation of bland, monomorphic spindle fibroblasts intercalated with collagenous stroma and prominent thick-walled blood vessels. Aberrant nuclear staining for β-catenin confirmed the diagnosis of desmoid-type deep fibromatosis (Figure 4).

Post-surgical course was uneventful and the patient was discharged on the 7th postoperative day. Currently he is undergoing outpatient oncologic follow-up.

Case 2

A 55-year-old man with a history of appendectomy and hypertension was admitted to the emergency department with fever (>38°C), abdominal pain associated, heartburn nausea, and reported bilious vomiting. No suspected symptoms of COVID-19 confirmed by negative thorax CT scan and negative NAAT tests for SARS-CoV-2 performed in the emergency department.

Physical examination revealed a distended abdomen with signs of peritonism. Laboratory test revealed only raised inflammatory markers (white blood cell, WBC 15.04 × 1000/mcL, C-reactive protein 16.86 mg/dL) with negative procalcitonin (0.22 ng/mL).

Abdominal computed tomography (CT) showed free air and an oval 8 cm mass located in the root of the ileal mesentery, characterized by contrast enhancement of the wall with a high density and air bubbles content, suspicious for an abscess or a stromal tumor (Figure 5). No family history of fibromatoses, FAP or abdominal trauma was reported.

The patient was eligible for emergency exploratory laparotomy which revealed diffuse fibrino-purulent peritonitis, resulting from spontaneous drainage of the abscess at the base of the ileal mesentery, but no evidence of perforation was found. In the small intestines multiple non-obstructive swellings of the ileal mesentery were found. Due to surgical difficulties to isolate an ileal loop that was tenaciously adhered to the mesentery and due to iatrogenic ischemia, a resection and mechanical side-to-side ileo-ileal anastomosis were performed.

Histologic diagnosis, limited by the paucity of the material, was of low-grade mesothelial proliferation.

The post-operative course revealed persistence of nausea and biliary vomiting. An enteral feeding catheter was placed. Due to feeding difficulties, persisting of symptoms, and not certain histologic diagnosis, a re-laparotomy was undertaken after 25 days and mechanical gastro-entero anastomosis was performed. An ileal loop was resected because of a massive retracting swelling of the ileal mesentery.

At grossing, within the mesenteric adipose tissue, pathologists found a firm, white, star-shaped lesion (3 cm in diameter) apparently retracting the bowel wall; no evidence of perforation was noted (Figure 6). Histology showed a hypocellular proliferation of spindle cells, immersed in a hyalinized thick stroma with very thin and compressed blood vessels. As the previous case, aberrant nuclear expression of β-catenin warranted a diagnosis of desmoid-type fibromatosis (Figure 7).

The immediate second postoperative course was characterized by symptoms of nausea which was successfully treated with fasting and prokinetics drugs.

The patient was transferred to the department of medical oncology in order to plan the best medical management after surgery.

Last update December 2020: In the latest CT scan, the first patient results apparently “disease-free.” The second one is undergoing second-line chemotherapy with MTXNAV (methotrexate-vinorelbine) due to the persisting of symptoms.

Desmoid-type fibromatosis (DF) accounts for 0.03% of all solid neoplasms and less than 3% of all soft tissue tumors [5]. Incidence is about 5–6 cases/1,000,000 per year [6] with a peak age of 30–40 years [7]. Although DF is mostly sporadic, studies report an association with familial adenomatous polyposis (FAP) in 5–6% of cases, and a patient with FAP has a 1000-fold higher risk of developing DF [8],[9],[10],[11].

According to their embryologic origin, desmoids tumor can virtually develop at any body site, but conventional DF can be divided into (a) extra-abdominal (60%) with a peak incidence between 25 and 30 years of age, and a predilection for the upper trunk and most commonly the upper extremities (approximately 30%) [12]; (b) abdominal wall (25%) most frequently in childbearing-age women within the first years from the pregnancy, also with oral contraceptives and following surgical procedures [13],[14]; (c) intra-abdominal (8–15%) particularly in the mesentery, retroperitoneum, and omentum, most often within the small bowel mesentery (the common primary tumor), where the neoplasm here are frequently large (up to 10 cm) [5],[13],[15]. This is the most aggressive type of DF because of its potential to infiltrate both pelvic and abdominal organs [5],[16],[17],[18],[19].

Pathogenesis of DF is multifactorial associated with physical, endocrine, and genetic causes and the pathological diagnoses are based on the investigation of assessment of morphological and immunohistochemical features [20],[21].

Both cases described here presented as an acute abdomen, but with some differences: the first one underwent emergency surgical resection due to bowel obstruction and the resection was performed with R0. The second one also underwent emergency surgical resection but due to perforation. In this case, resection was performed with positive microscopic margins resection R1.

In a non-emergency situation, there was no difference in event-free survival and long-term disease control between the patients undergoing surgery, and those managed with a conservative approach [22].

Active surveillance, under the supervision of an experienced team in connective tissue tumors from a referral center, can be suggested in an asymptomatic patient, independently of tumor size and site, despite the risk of progression being higher for larger tumors [23].

When active management for DF is necessary, surgery as first-line therapy can be considered, and wide (R0) microscopic margins resection should be the goal. Positive (R1) microscopic margins resection can be accepted when function or cosmesis is an issue, and there is insufficient evidence to recommend either perioperative radiotherapy or re-operation. When active management is required, but a surgical approach cannot be considered, and/or medical therapies are not available or not active, a moderate dose of radiotherapy has been shown to provide adequate local control [23].

An initial active surveillance approach, when active management is not required, is considered the first step after diagnosis in the majority of patients [23].

Regarding medical therapies, due to the lack of comparative studies, there is still no strong clinical evidence on which is the best therapy to use. Randomized data only exist for sorafenib, pazopanib, and methotrexate plus vinblastine. We can only assert that in a worst-case scenario with a mesenteric, potentially life-threatening DT there is consensus to administer more aggressive therapies [23].

Desmoid-type fibromatosis of the mesentery is a rare entity and the most aggressive form of DF because of its potential to infiltrate abdominal organs and related life-threatening complications [5],[16],[17],[18],[19].

Due to the rarity of these tumors, there are no clear guidelines on their management, the decision is left to the surgeon especially in emergencies situations. Emergent presentation requires emergency laparotomy.

The surgical approach of resectable intra-abdominal desmoid tumors with wide (R0) microscopic margins resection is the first-line treatment. In case of unresectable disease, non-surgical approach, such as radiotherapy and chemotherapy, is contingent on an accurate histologic diagnosis and is used to reduce the mass or inhibit tumor progression [23].

Experienced multi-disciplinary approach is recommended at the time of initial diagnosis, for optimal advice on the safety of an initial observation strategy [23].

In our cases, mesenteric fibromatosis was unusual since it was an incidental finding that required an emergency approach. In both cases, we performed R0 microscopic margins resection, although the significance of margins is still controversial in prognostic value [24].

Although uncommon, DF should be considered in the differential diagnosis when evaluating a patient with an abdominal mass of unknown origin presenting as acute abdomen in emergency settings.