Fibromatosis is a rare fibroblastic or myofibroblastic tumor of uncertain aetiology though genetic, hormonal factors, irradiation and trauma have been ascribed to its predisposition7–8. The incidence is 4–6/1,000,000 population per year, accounting for 0.03% of all tumours and 3% of soft tissue tumours8. There is increased association of fibromatosis with FAP and GS, associated with abnormalities in the APC gene. CTNNB1 mutations are observed in 90% of sporadic cases. Hormonal contribution is suggested by increased incidence of fibromatosis during and after pregnancy. Fibromatosis developing after previous surgery, irradiation or trauma is also observed7–8. Our patient is a sporadic case with no history of FAP or GS. Her last pregnancy was in 2008, fourteen years earlier than the episode of intestinal obstruction and is unlikely a contributing factor in the development of fibromatosis. There was also no history of previous abdominal surgery, trauma or irradiation. There were apparently no predisposing causes or antecedent events in our patient.
Fibromatosis is classified as superficial or deep7–9. It is a recurrent disease without metastatic potential. Deep fibromatosis is more prone to recurrence and regarded as a borderline tumour. It includes extra-abdominal, abdominal and intra-abdominal types. Among intra-abdominal types, mesentery fibromatosis is more common than that of the ileocecal ligament, omentum or retroperitoneum8. Fibromatosis grows rapidly initially followed by slow progression to involve nearby structures, causing symptoms related to the anatomical involvement. Intra-abdominal fibromatosis is mostly asymptomatic or may present as abdominal distension or mass. Intestinal obstruction, intestinal perforation with acute peritonitis or symptoms related to compression of adjacent anatomical structures such as ureteric obstruction are less common presentations of fibromatosis1–2, 8. Our patient presented as intestinal obstruction, an uncommon presentation.
The histology of fibromatosis is myriad, requiring full recognition for diagnosis. There are seven histological patterns10; conventional, hypocellular/hyalinized, staghorn vessel, myxoid, keloidal, nodular fasciitis-like and hypercellular. Most fibromatosis manifest several patterns with the mean number of two. The conventional pattern is the most common and is present in almost all cases. In all patterns, the spindle-shaped fibroblasts and myofibroblasts have bland pale-staining nuclei, inconspicuous nucleoli with or without mild cytological atypia and minimal mitotic activity. The histology of our case was unusual, lacking the conventional pattern and exhibits prominent NF-like and staghorn vessel patterns. This poses NF and solitary fibrous tumour (SFT) the two most important differential diagnoses. Fibromatosis is distinguishable by nuclear β-catenin expression and genetic changes related to β-catenin/Wnt signalling pathway1–8,11−13. Though β-catenin immunopositivity is not entirely specific for fibromatosis7, its morphologic differences from the mimickers and the different immunophenotypic and genotypic features of these various conditions enable their distinction. NF, a major differential diagnosis in our patient, is negative for nuclear β -catenin staining immunohistochemically. Further, NF lacks staghorn vessels present in our case. NF is also characterized by USP gene rearrangement14. SFT may be more problematic as it morphologically may also manifest keloidal fibres, staghorn vessels and that 40% may be nuclear β-catenin positive. It is however distinctive in STAT-6 positive immunophenotype15. Other differential diagnoses of fibromatosis encompass various malignant/borderline spindle cell tumours (spindle cell carcinoma and melanoma, leiomyosarcoma, malignant peripheral nerve sheath tumour, synovial sarcoma, angiosarcoma, fibrosarcoma and gastrointestinal stromal tumour). These tumours could be easily distinguished by their characteristic morphology, immunophenotypes and genotypes. Differential diagnoses7 from reactive fibroblastic/myofibroblastic proliferations, myxoma, keloid, sclerosing mesenteritis/idiopathic retroperitoneal fibrosis (Ig4-related disease) and inflammatory myofibroblastic tumour (IMT) can usually be made by differences in morphology, immunophenotypes and nuclear β-catenin positivity in fibromatosis. IMT may morphological range from bland to atypical spindle cells with frequent ALK immunopositivity and ALK gene rearrangement, allowing its distinction from fibromatosis7.
The treatment of asymptomatic fibromatosis could be surveillance. In emergencies such as intestinal obstruction, treatment is surgical intervention. Recurrence occurs in about 50% of deep fibromatosis, and is related to age (younger age being a risk factor), tumour location and resection margin status8. Wide negative resection margins are associated with a lower recurrence rate, compared with positive margins (10% vs 80%)7–8. Negative resection margins in our patient portend an expected lower recurrence rate. Other treatment modalities are radiotherapy or systemic therapy (hormonal, cytotoxic drugs, targeted therapy)8.
To conclude, we reported a rare case of intestinal obstruction caused by intra-abdominal intestinal/mesenteric fibromatosis which required urgent surgery. Wide surgical excision with negative resection margins in our case should confer a lower recurrence rate. The tissue diagnosis was challenging due to the prominent NF-like and staghorn vessel patterns, but was confirmed by bland-looking fibroblastic proliferation with infiltrative border, β-catenin nuclear staining and negative immunostaining for markers of its mimickers. Distinction from various other spindle cell tumours and malignancies is important as the post-surgical management and prognosis are materially different from fibromatosis.