• Lymph node
• myofibroblastoma
• amianthoid fibre
• lymph node pathology

Intranodal palisaded myofibroblastoma (IPM) is a rare lymph node lesion that has been recognised as an entity since 1989, initially having been known by different names, including ‘solitary spindle cell tumour with myoid differentiation of the lymph node’1 and ‘intranodal hemorrhagic spindle cell tumour with amianthoid fibres’.2 More than 50 cases have now been described, the majority of which have involved inguinal lymph nodes. The tumour is slightly more common in men and occurs over a wide age range (19–71 years).3 We report another case and discuss the nature, nomenclature and differential diagnosis of this entity.

A 74-year-old man presented with a 2-year history of a lump in the right groin, which had recently increased in size. On examination it was found to be firm, mobile and non-pulsatile. There was no surrounding inguinal lymphadenopathy. An ultrasound scan revealed a focal solid area (2×2 cm) of mixed echogenicity with some vascularity. Possible differential diagnoses were thought to be fat necrosis, calcifying epithelioma or epidermal cyst. The mass was excised and macroscopically it was a smooth grey nodule, 30 mm in maximum dimension, with a solid fibrous cut surface that appeared slightly gelatinous. Microscopy showed a tumour arising within a lymph node, with a capsule and peripheral rim of lymphoid tissue (figure 1) surrounding the well-demarcated tumour, which was composed of a fascicular proliferation of spindle cells with focal nuclear palisading (figure 2). Acellular stellate-shaped collagen rich amianthoid fibres were evident throughout the lesion. Immunohistochemistry was performed which showed diffuse strong positivity for smooth muscle actin (SMA) and strong nuclear positivity for cyclin D1 in more than half of the nuclei (figure 3). Desmin, S100, epithelial membrane antigen and p63 were all negative. CD34 highlighted the amianthoid fibres but was negative in the lesional cells. A diagnosis of IPM with amianthoid fibres was made. The patient was well at 6-month follow-up.

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Figure 1

Low power view of nodal mass (left) with peripheral rim of lymphoid tissue and areas of fresh haemorrhage (right).

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Figure 2

Proliferation of bland spindle cells with areas of nuclear palisading and interspersed amianthoid fibres.

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Figure 3

Diffuse positivity for smooth muscle actin (left) and nuclear staining with cyclin D1 (right).

IPM is a rare mesenchymal lymph node neoplasm characterised by a bland spindle cell proliferation, showing areas of nuclear palisading, admixed with extravasated red blood cells in areas of haemorrhage and bounded by a pseudocapsule and rim of compressed nodal tissue.4 Dispersed throughout the tumour are so-called amianthoid fibres, which are of smaller calibre than true amianthoid fibres and are composed of a core of type I collagen surrounded by type III collagen.5 Such fibres are not pathognomonic of IPM and have been described in other mesenchymal tumours.2

The spindle cells of IPM show positive immunohistochemical staining for SMA and vimentin but are negative for S100 protein, glial fibrillar acidic protein, CD34, desmin, cytokeratins and epithelial membrane antigen, with a low proliferation index.4 6

It was originally suggested that IPM originates from smooth muscle-like cells of blood vessels present in lymph nodes, being particularly prominent in nodes of the groin. More recently, the pathogenesis of IPM has been postulated to be linked, at least in part, to cyclin D1 overexpression,6 as demonstrated immunohistochemically in the current case.

The finding of a spindle cell lesion in a lymph node raises several other diagnostic possibilities, including Kaposi sarcoma, schwannoma, spindle cell haemangioma, inflammatory myofibroblastic tumour, spindle cell melanoma, spindle cell carcinoma and dendritic cell sarcoma/tumour. Morphologic and immunohistochemical features enable distinction between these entities (table 1). As is evident, not all of the immunohistochemical markers presented in the table were performed in our case. The panel chosen may be tailored according to the microscopic features.

Another mesenchymal lesion that most commonly occurs in the inguinal/groin region is mammary-type myofibroblastoma, which shows an apparent predilection for occurence along a milk-line extending from the axilla to the groin, possibly due to tissue in this anatomic distribution being hormone sensitive. Both mammary-type myofibroblastoma and IPM, despite being named in relation to ‘myofibroblasts’, do not in fact show ultrastructural evidence of myofibroblastic differentiation, with a lack of the distinctive fibronexus.7 Instead, both lesions show features of smooth muscle differentiation. However, the immunohistochemical staining of these two lesions differ, with IPM classically positive for SMA and not desmin whereas mammary-type myofibroblastoma shows diffuse desmin expression with SMA positive in only one-third of cases.8 In view of these features, perhaps the original, more descriptive designations of IPM, such as intranodal haemorrhagic spindle cell tumour with amianthoid fibres, may have been preferable, as they were not misnomers.

IPM is a benign tumour with occasional local recurrence reported but no cases that have undergone distant metastasis.3 4 The importance of this tumour lies in its recognition and distinction from other, more aggressive neoplasms.