Teaching Case

A 49-year-old female patient presented with a progressively growing swelling of the neck for 1 year, until it was complicated by dyspnoea. No relevant medical history. No history of surgery or smoking.

A cervical CT scan showed a retropharyngeal tumour extending from C2 to the thoracic inlet measuring 111x42x30 mm, with local mass effect and erosion of the vertebral bodies adjacent to it. Contrast enhancement was avid and homogenous (Fig. 1, 2). There was no calcification or lymphadenopathy. The patient underwent surgery with unsuccessful resection due to neurovascular and bone involvement and a final tracheotomy was performed. Histopathology of biopsy confirmed a desmoid tumour.
On MR imaging which was performed 3 months after radiotherapy, the lesion had isointense T1 signal compared to muscle and hypointense T2 signal, with moderate heterogeneous enhancement after gadolinium administration. The tumour was relatively stable in size (Fig. 3).

Desmoid tumours or fibromatosis are a benign lesion with a great propensity for local extension and recurrence [1].
They are most frequent in patient with familial adenomatous polyposis (FAP) and Gardner ’syndrome [2]. Other risk factors, such as trauma, surgery, pregnancy or taking oral contraceptives have been reported [3]. Furthermore, genetic factors have been identified in patients with desmoid tumours [3].
They typically occur in the abdominal wall or within the abdomen but also may occur extra-abdominally [3].
They correspond to a clonal proliferation of well-differentiated fibroblasts arranged in bands in a matrix of collagen fibres, the mitotic index is low and there are no nuclear atypia [4].
These tumours represent 0.03% of all solid neoplasias [1]. They preferentially affect women (sex-ratio 2/1), with an average age between 20 and 40 years [1].
Aggressive fibromatosis in the head and neck has been reported to constitute approximately 11% of extraabdominal cases [4].
They generally present as a painless swelling that has been present for less than a year, often fixed to underlying muscle or bone but not to the skin [1].
Imaging has an important role in the diagnosis and monitoring of desmoid tumours. Ultrasound allows the exploration of superficial locations showing a hypoechoic and homogeneous lesion with variable vascularization on Doppler [3]. On CT, it appears as an isodense lesion compared to the muscle as illustrated in our case. After contrast administration, the lesions are usually hyperdense, but can be isodense or hypodense [5]. On the CT examination in our case, the tumour followed these more common attenuation characteristics. MR is more specific for the evaluation of tumour boundaries. On T1W, desmoid tumours are isointense compared with the muscles. Their signal on T2W is usually intermediate. In cases of major cellularity or myxoid components, the T2 signal is higher. However, if the collagen contingent is predominant, the signal is reduced as it was observed in our case. Finally, contrast enhancement after injection of gadolinium chelates is also variable, more intense when the lesion is highly cellular [3].
The only curative treatment is wide surgical excision, but the risk of local recurrence is high [1]. Several adjuvant or complementary treatments have been proposed and the results are promising [2].
Our patient had an extremely rare location for a desmoid tumour but clinical history, CT and MR characteristics and evolution were compatible with this. Surgical biopsy confirmed the diagnosis.