Intranodal Palisaded Myofibroblastoma. (IPM)

Initially the lesion was defined as a malignant neurilemmoma by Deligdish et al. in 1968 and by Katz et al. in 1974. In 1989, three independent groups of investigators described this tumor, giving it different names. Weis et al proposed the name “palisaded myofibroblastoma”, Suster et al. “intranodal hemorrhagic spindle-cell tumor with amianthoid fibers” and Lee et al.  “solitary spindle-cell tumor with myoid differentiation of the lymph node”.
Less than 100 cases described so far.  IPM commonly affects the 2^nd to 8^th decade, with a peak incidence between 40 - 60 years of age. Occurrence of this tumor in infants has been reported. Most often inguinal lymph node is affected, but lesion is seen also from neck, axilla and mediastinum. No metastases, but single recurrences reported.
Histology shows some variation but palisading of cytologicaly bland nuclei of spindle cells is characteristic and found in almost all cases. Mild nuclear atypia is rare. Stroma is finely collagenous or myxo-collagenous with hemorrhages and hemosiderin. Eosinophilic collagenous bodies and eosinophilic intracytoplasmic inclusions (highlighted by Actin staining) are often found. Expression of Actin (SMA), Vimentin and Cyclin D1 (often in >50% of spindle cells) and a low proliferating index of Ki-67 are typical. In 2015 Miettinen et al. showed frequent mutations of β- Catenin gene and nuclear expression of  β-Catenin in absolute majority of cases, which explains also the overexpression of Cyclin D1 (via Wnt signaling pathway).
In some publications the IPM has been associated with the infections from Epstein-Bar Virus (EBV) and Human Herpes Virus-8 (HHV-8) but no final proof is presented yet.

• Kandemir NO, Barut F, Ekinci T, Karagülle C, Ozdamar SO. Intranodal palisaded myofibroblastoma (intranodal hemorrhagic spindle cell tumor with aminathoid fibers): a case report and literature review. Diagn Pathol. 2010 Feb 9;5:12. doi: 10.1186/1746-1596-5-12.
• Koseoglu RD, Ozkan N, Filiz NO, Kayaoglu HA, Aydin M, Culha EN, Ersoy OF. Intranodal palisaded myofibroblastoma; a case report and review of the literature. Pathol Oncol Res. 2009 Jun;15(2):297-300. doi: 10.1007/s12253-008-9122-0. Epub 2008 Nov 8.
• Laskin WB1, Lasota JP, Fetsch JF, Felisiak-Golabek A, Wang ZF, Miettinen M. Intranodal palisaded myofibroblastoma: another mesenchymal neoplasm with CTNNB1 (β-catenin gene) mutations: clinicopathologic, immunohistochemical, and molecular genetic study of 18 cases. Am J Surg Pathol. 2015 Feb;39(2):197-205. doi: 10.1097/PAS.0000000000000299.
• Nguyen T, Eltorky MA. Intranodal palisaded myofibroblastoma. Arch Pathol Lab Med. 2007 Feb;131(2):306-10.