PMC3171926_01
Representative image of the inflammatory myofibroblastic tumor (IMT) in the distant tracheal portion in a 57-year-old lady. (a) Overview of the lesion spanning three cartilage rings (PAS). (b) Note the partly spindly architecture of the lesion, with only very mild nuclear atypia and absent mitotic activity (H&E). Immunohistochemical documentation of CD68 expression (clone PGM1, (c)) and of ALK1 expression (d). The lower four panels (e)-(h) depict representative images of one of 15 peritracheal lymph nodes in the vicinity of the tracheal lesion shown in panel (a). (e) Overview over the deep sections through the lymph node, which shows that the granulomatous lesions largely replaces the lymph node and focally transgresses its capsule (H&E). (f) Higher power magnification of the marked area in (a). Note the striking granulomatous reaction replacing large parts of the lymph node, with extensive extracapsular extension into the adjacent adipose tissue. Immunohistochemical documentation of CD68 expression (clone PGM1, (g)) and absence of ALK1 expression (h). The space bars represent 0.5 cm in (a), 1 mm in (e), and 100 mum in (b)-(d) and (f)-(h).
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About one month after laser resection, the patient was referred to the thoracic surgery center of the Lausanne University, medical center, where the lesion was entirely resected transthoracically with a 2.1 x 2.2 cm tracheal fragment (Figure 1(a)).  Histological Examination of the Tracheal Lesion showed a dense proliferation of spindle cells, partly with an epithelioid aspect, arranged in well-organized fascicles (Figure 1(b)). The lesion had a total thickness of 0.5 cm, traversing the tracheal mucosa, but without invasion into the adjacent cartilage (Figure 1(a)). By immunohistochemistry, the tumor cells showed a cytoplasmic decoration with antibodies to CD68 (both KP-1 and PGM1, Figure 1(c)), S-100 and of ALK1 (Figure 1(d)). The granulomas were very well delimited, sometimes confluent into large masses, with an admixture of multinucleated giant cells, but with no evidence of caseous necrosis (Figures 1(e) and 1(f)). In at least one large lymph node, the capsule was transgressed by the granulomatous reaction, extending widely into the adjacent adipose tissue, focally associated with coagulation necrosis (Figures 1(e) and 1(f)). By immunohistochemistry, the epithelioid cells reacted positively with CD68 (PGM1, Figure 1(g)) and focally with S-100, with an admixture of mostly CD4 positive (T-), less frequent CD20-positive (B-) lymphocytes. No reaction was detected with CD1a, nor with ALK-1 (Figure 1(h)), despite repetition of the reaction in parallel with the tracheal lesion, in which ALK-1 positivity was confirmed (Figure 1(a)). Arguments against this idea are the reported rarity of IMT metastases into single, let alone multiple lymph nodes and the different histomophological appearance and immunostaining pattern (see Figure 1). 
PMC3171926_02