Myofibroblastic Tumour

ICD-O:8825/1

Inflammatory myofibroblastic tumour (IMT) is clinico-pathologically a well-defined fibroinflammatory proliferative lesion with unpredictable biological behaviour. Lung, gastrointestinal and genitourinary tract systems are the commonest sites for IMT, although the lesion has been reported throughout the body [382]. It rarely affects the head and neck region, and only a few well documented IMTs have been found in the larynx and pharynx [65, 96, 167, 188, 382].

The aetiology of the lesion is unknown, but different infections with an exaggerated response to some unknown microorganism or post-traumatic events have been attributed as causal factors [9, 76, 167, 382]. Most reported laryngeal IMTs are polypoid or pedunculated lesions that occur in the true vocal cords or in the subglottic area. Hoarseness, foreign body sensation, dyspnoea and stridor are presenting symptoms. Patients with laryngeal IMTs are mainly adult males [382].

Histologically, IMT is composed of myofibroblas-tic spindle cells, admixed with a prominent infiltrate

Fig. 7.9. Inflammatory myofibroblastic tumour. Lesion is composed of uniform spindle cells, intermingled with inflammatory cells

of lymphocytes, plasma cells and neutrophils. The nuclei of the spindle cells are elongated, slightly polymorphous, containing one or more small nucleoli, the cytoplasm is palely eosinophilic (Fig. 7.9). Occasional regular mitoses are seen. Inflammatory cells are unevenly distributed within the lesion.

Three basic histological patterns have been described:

1. Myxoid/vascular pattern, resembling inflammatory granulation tissue;

2. Compact spindle cell pattern with fascicular and/or storiform areas with various cellular density;

3. Hypocellular pattern, densely collagenised and reminiscent of a fibrous scar [64].

Immunohistochemistry confirms the myofibroblastic phenotype of the spindle cells, which are typically reactive to vimentin, smooth muscle actin, and muscle-specific actin [64, 382]. Additionally, ALK1 and/or p80 were reported in a cytoplasmic pattern in 40% of cases of IMT [56]. Both markers are useful indicators of a 2p23 abnormality, suggesting the neoplastic nature of positive cases of IMT. However, it must be interpreted in the context of histologic and other clinicopathologic data if used as an adjunct to differential diagnosis [56].

Radical excision of the lesions has been reported to be curative in more than 90% of extrapulmonary IMTs, including head and neck lesions [63]. Six out of seven patients with laryngeal IMTs in Wenig's series were free of disease over periods of 12 to 36 months after complete excision. In one patient, laryngectomy was required after recurrence of the disease [382]. A metastatic potential has been exceptionally noted in patients with abdominal and mediastinal IMTs. However, a fatal outcome of a patient with IMT of the paranasal sinuses has

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