This pathology review focuses on the histological features and differential diagnosis of Myofibroma, a benign mesenchymal tumor. The speaker describes Myofibroma as a typically biphasic tumor characterized by alternating components: hypocellular, eosinophilic, or often bluish/mixoid-appearing "myoid nodules," and hypercellular interstitial zones. These cellular areas are composed of primitive, bland spindle cells often associated with prominent, dilated, branching vessels resembling a staghorn or hemangiopericytoma-like pattern. The presentation discusses why the tumor's multi-nodularity often leads to confusion with tumors like Plexiform Neurofibroma or Mixoid/Chondroid tumors. Historically, this lesion was sometimes misclassified as infantile hemangiopericytoma. Myofibromas are generally benign, though multifocal involvement in infants (myofibromatosis) can rarely be fatal if internal organs are involved. The video concludes by differentiating Myofibroma from Myopericytoma based on the presence of distinct hypocellular myoid nodules.
Myofibroma: Histological Features and Diagnosis
0:29 Identifying Myofibroma: Myofibroma is the correct diagnosis, noted as a tumor that is easy to identify after seeing a few cases, but often confusing at first glance.
0:38 Biphasic Morphology: The tumor exhibits a biphasic pattern consisting of distinct nodules and a surrounding cellular substance.
0:42 Myoid Nodules (Phase 1): These nodules are supposedly myofibroblastic/muscle-like (myoid), staining pink (eosinophilic). However, they are often predominantly blue, mixoid, or pseudochondroid-appearing (1:01), which is a key diagnostic pitfall often leading to misdiagnosis as a cartilaginous or mixoid tumor.
1:33 Cellular Areas (Phase 2): The areas between the nodules are filled with primitive, cellular, bland, round-to-spindle cells (1:40). These cells are similar to those seen in myopericytomas.
2:22 Vascular Pattern: The cellular areas often contain prominent, dilated, branching vessels, giving a staghorn or hemangiopericytic appearance.
2:30 Historical Context: The tumor previously known as Infantile Hemangiopericytoma is now recognized as an exuberant form of Myofibroma, and the use of the older term is discouraged.
2:55 Benign Nature and Clinical Presentation: Myofibromas are entirely benign. They rarely recur even after incomplete removal and sometimes regress spontaneously (3:05).
3:08 Clinical Range: Most recognized in children (where they can be multifocal—infantile myofibromatosis). If internal organs are involved (e.g., lungs), the condition can be serious or fatal (3:15). Myofibromas can also occur as solitary lesions in adults or elderly patients (3:30).
3:48 Differential Diagnosis (Plexiform Neurofibroma): The tumor's multi-nodularity can be confused with Plexiform Neurofibroma (PN). The key difference is that PN exhibits "twisty infiltrating nerve trunks" (4:00), whereas Myofibroma's nodules have a distinct myoid/pseudochondroid nature.
5:06 Unique Pediatric Feature: A viewer noted that in pediatric cases, it is common to see less cellular areas bulging and growing into vessel lumens.
7:26 Differentiating from Myopericytoma: Both Myofibroma and Myopericytoma are related and generally benign (WHO groups them similarly). The main morphological distinction is that Myopericytoma is composed entirely of whirling cellular pericytes and lacks the hypocellular myoid nodules seen in Myofibroma.