Infantile fibromatosis is a benign tumour that consists of dense masses of fibroblasts and myofibroblasts with marked collagen production. Although it is a nonmetastasising tumour, it has significant potential for local invasion and recurrence and may be fatal because of its size and location. The authors report an unusual case of infantile fibromatosis of the cheek in an 8-month-old boy, present since birth. The patient underwent surgical treatment with tumour-free margins and the 6-month follow-up revealed no signs of recurrence. Infantile fibromatosis of the cheek is a very rare condition at this location, especially congenital cases. It should be considered in the differential diagnosis of congenital lesions in childhood.
The fibromatoses are characterized by proliferation of fibroblasts and myofibroblasts with marked collagen production. The cells are spindle-shaped or oval, bland and uniform, without pleomorphism or giant cells. Clinically, they are hard tumours which can infiltrate locally and recur, sometimes repeatedly and especially when incompletely excised, but which do not metastasize so they are technically benign .
Fibromatoses occurring at extra-abdominal sites are most common in patients between puberty and 40 years of age with only 5% in those 10 years or less. E nzinger & W eiss have observed the following incidences: head and neck 34% of the cases, shoulders and upper arm 32%, trunk 18% and thigh 16% . In the head and neck more than 54% of the lesions are present in soft tissues adjacent to mandible, 19% in parotid or cheek region, 7% in tongue, 7% in maxillary gingiva and palate, and more than 4% in the lip .
Infantile fibromatosis (IF) represents the childhood counterpart of extra-abdominal fibromatosis in adults . It is generally treated by excision of the lesion, including a margin of healthy tissue. Complete excision is often accompanied by deformity and/or functional disability because IF may involve extensive areas of the maxillofacial region. Alternative modes of therapy have been suggested for lesions considered inoperable or associated with functional disability . Management of the condition remains unclear because of the rarity of the disease, and general recommendations for clinical management of residual or recurrent disease are lacking.
A review of the English language literature shows that there are 11 previous reports of IF in the cheek . The aim of this article is to report a rare case of congenital IF of the cheek describing its clinical, radiographic, histological and immunohistochemical features, and to discuss the related literature and differential diagnoses.
An 8-month-old boy was referred to the oral pathology clinic of the João de Barros Barreto University Hospital, with a chief complaint of dysphagia, limited mouth opening and a painless swelling in the region of the right cheek, present since birth ( Fig. 1 ). The parents related that the mass had slowly enlarged until the date of the evaluation. There were no abnormalities in pregnancy, delivery and growth of other organs. His family history and review of systems were noncontributory.
Under physical examination, the patient appeared otherwise healthy. No enlarged cervical lymph nodes were palpable. On intraoral examination, a smooth, firm swelling was palpable in the right cheek with no apparent expansion to the buccal or palatal cortical plate of the maxilla or tooth mobility. The overlying mucosa appeared intact and normal.
Magnetic resonance imaging (MRI) revealed a soft tissue mass in the right cheek region, with neither cystic nor fatty components. In the axial view, the T1 weighted image showed a latero-lateral expansion of the lesion involving the right lateral pterygoid muscle ( Fig. 2 A ); and the T1 weighted sequence, coronal view, showed a high signal lesion, well defined, occupying the masticatory space ( Fig. 2 B). The mass appeared to have caused some bony erosion of the lateral aspect of the right maxilla. The patient underwent incisional biopsy. A histologic frozen section did not reveal signs of malignancy. The lesion was completely excised en bloc with tumour-free margins.
Microscopic examination revealed an unencapsulated proliferation of neoplastic tissue composed of spindle-shaped fibroblastic cells within abundant collagen fibres, arranged in fascicular to interlacing patterns ( Fig. 3 A ). Neoplastic cells showed no nuclear atypism or pleomorphism and mitotic figures were absent or scarce ( Fig. 3 B).
Immunohistochemistry revealed that the neoplastic cells were strongly positive for vimentin (DAKO, 1:2000) ( Fig. 4 A ) and α-smooth muscle actin (DAKO, dilution 1:50) ( Fig. 4 B), and focally positive for desmin (DAKO, 1:2000) ( Fig. 4 C) and calponin (DAKO, dilution 1:150) ( Fig. 4 D). They were negative for S-100 protein (DAKO, dilution, 1:800) and muscle specific actin (HHF-35) (DAKO, dilution 1:50). These reactions confirm the diagnosis of infantile fibromatosis.
The postoperative course was uneventful. At the time of writing, the patient had been under regular follow-up for 6 months and remained free of recurrence or new lesion as proven by CT scans and lack of clinical findings.
IF is a benign tumour arising from connective tissue, the fascial sheaths, and musculo-aponeurotic structures of muscle. The tumour consists of dense masses of fibroblasts with a poorly defined margin making complete surgical excision difficult. Although IF is a nonmetastasising tumour, it has significant potential for local invasion and recurrence and may be fatal because of its size and location . To the authors’ knowledge, 11 cases of IF in the cheek have been described in the English language literature. In the present article, the authors report a rare case of IF of the cheek, this is only the second case arising congenitally.
Few data are available concerning the incidence. The estimated incidence in the general population is 2–4/1,000,000/year. No significant racial or ethnic distribution is reported . In the head and neck region, F owler et al. reviewed four congenital cases in the oral and paraoral region with no defined location. The literature reveals only one recognized case of congenital fibromatosis in the cheek , so it is thought that congenital cases in the cheek are rare.
IF usually manifests as a slow growing solitary mass within muscle tissue, showing a variable histological picture largely dependent on the age of the child. Lesions occurring in children of 2 years or older tend to be more cellular and consist of interlacing bundles of fibroblasts associated with varying amount of collagen. Some of these blend with lesions that are virtually indistinguishable from adult forms of extra-abdominal desmoids . In contrast, lesions found chiefly in infants during the first few months of life, are characterized by small, haphazardly arranged, round or oval cells deposited in a myxoid background . Despite the pathological variants, there is no difference in clinical tumour behaviour between these two types .
In the present case, the differential diagnosis included congenital/infantile fibrosarcoma, spindle cell type embryonal rhabdomyosarcoma (ERMS) and desmoplastic fibroma. The most difficult problem in the differential diagnosis is distinguishing the more cellular variants of IF from congenital/infantile fibrosarcoma. The latter tumour resembles the adult form of fibrosarcoma, with characteristic high cellularity, arrangement in a uniform herringbone pattern, and a high mitotic rate . In some cases, distinction between these entities is difficult, if not impossible. Cytogenetic and molecular genetic analyses are highly reliable in determining this distinction because congenital/infantile fibrosarcoma is characterized by a t(12;15)(p13;q25), which is not found in IF .
The distinction from fibromatosis is not necessarily critical, as both behave and are managed similarly (i.e. by adequate local excision) . The spindle cell type of ERMS is a rare subtype that accounts for 4% of all RMS, with the head and neck as the second most common site of involvement . Histologically, this variant has a uniform appearance that resembles smooth muscle tumours . The immunohistochemical analysis consistently reveals expression for myogenic antigens, including HHF-35 and desmin , unlike the case reported where the HHF-35 was negative and desmin was focally positive. Desmoplastic fibroma represents the osseous counterpart of the soft tissue fibromatosis with the mandible as the most common site of involvement . Microscopically, desmoplastic fibroma arising within bone cannot be separated from extra-abdominal fibromatosis of soft tissue infiltrating bone. In these cases, clinical and radiographic features are critical in the separation of these two entities . Determination of origin in more advanced lesions is problematic and may be arbitrary.
Immunohistochemistry has been an immensely helpful tool in diagnosing challenging and otherwise histologically indistinct lesions ( Table 1 ). The tumour cells of IF show uniform strong vimentin positivity; as expected, given that it is a recognized fibroblastic entity. A subset may also stain for desmin and muscle-selective isoforms of actin to a variable extent; a feature that is also seen in a number of other neoplasms from muscular origin that may be included in the histopathologic differential diagnosis. The reproducible reactivity for S-100 protein amongst peripheral nerve sheath tumours is useful for distinguishing these lesions from IF, since the expression of this marker in IF is absent . Calponin is a cytoplasmic protein that binds to actin in myoepithelial and smooth muscle cells. IF typically demonstrate intermediate to strong cytoplasmic staining for this marker. Another useful marker is beta-catenin, which is a transcription factor stored as an inactive protein complex in the cytoplasm of the cell. When activated, it translocates to the nucleus to drive cell proliferation. 80–100% of fibromatosis stains positively for nuclear beta-catenin . In the present case, the neoplastic cells stained positively for vimentin, desmin, calponin and α-smooth muscle actin, confirming myofibroblastic differentiation.
|Lesions||Desmin||Vimentin||S-100||α-Smooth muscle actin||Muscle specific actin (HHF-35)||Calponin||Beta-catenin|