Case Presentation - Summer, 2009

Intranodal Palisaded Myofibroblastoma

NOTE: The diagnosis and analysis for this case study were provided by an independent physician. All conclusions and opinions are those of the physician and not Hologic, Inc.

History: 62 year old male

Specimen type: Right Inguinal Lymph node FNA

Case provided by: The laboratory providing the specimen prefers to remain anonymous

Intranodal palisaded myofibroblastoma (IPM) is a rare benign lesion of the lymph node that is derived from myofibroblasts or smooth muscle cells. It usually presents as a painless and slow-growing inguinal node. Patients with this lesion usually notice a groin mass, but since it is asymptomatic, may not seek medical attention. Although IPM almost always arises in the inguinal lymph nodes, occurrence in mediastinum and submandibular lymph nodes has been reported. It can occur in a wide range of ages, from 19 to 78 years. No pediatric cases have yet to be reported. Case reports (42 cases from 13 publications) suggest that there is a slight predominance in males over females (2:1 ratio). IPM doesn't seem to show any predilection for race and has been reported in people of white, African and Asian descent.

Initial case reports of IPM were published in 1968 and 1974. Originally, IPM wasn't well characterized and as a result was thought to belong to the schwannoma/neurilemmoma family. From 1968 to 1989, IPM was diagnosed as an intranodal form of schwannoma or as leiomyoma. The established characterization of IPM didn't occur until 1989 when 3 different groups published their findings. Intranodal palisaded myofibroblastoma was once referred to as intranodal hemorrhagic spindle-cell tumor with amianthoid fibers and solitary spindle cell tumor with myoid differentiation of the lymph node.

Surgical removal of this tumor is almost always curative. There is an approximate 6% chance of recurrence and no known malignant potential.

Macroscopic features
Upon gross inspection, the most common feature of intranodal palisaded myofibroblastoma is dark red areas of hemorrhage. These areas may be focal, multifocal or diffuse. IPM grows from the interior portion of the lymph node outward toward the periphery. As a result the normal lymphoid tissue is compressed to the periphery.

Microscopic Features
There are five distinct histological features of intranodal palisaded myofibroblastoma. The first feature is hemorrhage and a collagenous pseudocapsule located at the point where the remaining lymph node parenchyma is compressed and against the capsule. Second, the cells are bland spindle cells with abundant areas of nuclear palisading similar to the antoni- A pattern found in schwannomas. Third, intraparenchymal hemorrhage and extravasation of red blood cells are present between spindle cells. The presence of collagenous bundles of so-called amianthoid fibers are distributed throughout the lesion. These bundles have a darker eosinophilic center surrounded by a paler eosinophilic, stellate-shaped periphery. This feature is not pathognomonic to IPM due to the fact that other tumors demonstrate collagenous amianthoid change. Aminathoid changes have been noted to be present in virtually all cases. Therefore, the presence of these changes along with the other features of IPM helps to solidify the diagnosis. Lastly, extracellular and intracellular fuchsinophilic bodies are present in IPM. The fuchsinophilic bodies stain red with trichome stain and exhibit positive muscle specific actin reactivity in immunohistochemical studies. These bodies are very difficult to detect under light microscopy using hematoxylin-eosin stain but can be easily identified using smooth muscle actin immunohistochemical stain.

The use of immunohistochemical studies can be very helpful in confirming the diagnosis of IPM. IPM stains positive for both vimentin and muscle specific actin. It has a strong expression of cyclin D1 and a low proliferative index of Ki-679. Neural markers such as S100 and glial fibrillary acidic protein, along with endothelial markers like CD 34 and desmin are all negative. The center of the so called amianthoid fibers is made up of collagen type I, while the periphery is composed of collagen type III.

Differential Diagnosis
Although there are many soft tissue tumors that may mimic intranodal palisaded myofibroblastoma, histological features can help narrow down the differential diagnosis to the following lesions: schwannoma, Kaposi sarcoma (KS), hemangioendothelioma, and metastatic tumors.

  1. Intranodal Palisaded Myofibroblastoma.
  2. Nguyen T,et al. Intranodal Palisaded Myofibroblastoma. Arch.Pathol.Lab Med,Feb 2007[306:IPM]2.0.CO;2