This transcript provides a detailed pathology review of Myofibroma, focusing on its classic biphasic histological structure and its differentiation from similar tumors. Myofibroma is characterized by hypocellular, often blue/pseudochondroid, "myoid nodules" separated by hypercellular zones. These cellular areas consist of primitive round-to-spindle cells and display prominent vascularity, including dilated, branching vessels reminiscent of a hemangiopericytic (staghorn) pattern. The speaker notes that the former diagnosis of "infantile hemangiopericytoma" is now considered an exuberant form of myofibroma. Although histologically confusing and often mistaken for tumors like plexiform neurofibroma due to multi-nodularity, Myofibroma is fundamentally a benign tumor. While typically a solitary lesion in adults, its multifocal presentation in infants can be serious or fatal if internal organs are involved. The video concludes by contrasting Myofibroma with Myopericytoma, emphasizing that the presence of myoid nodules is the key distinguishing feature.
Myofibroma: Histology, Differential Diagnosis, and Clinical Behavior
0:29 Myofibroma Identification: The tumor is identified as Myofibroma, a lesion that can be confusing at first glance but becomes recognizable after seeing a few cases.
0:38 Biphasic Tumor Structure: Myofibroma is characterized by a biphasic morphology consisting of two main components.
0:42 Myoid Nodules: The first component consists of distinct nodules, termed "myoid nodules." Although pink/muscle-like (myofibroblastic), they often appear blue, mixoid, or pseudochondroid (1:01), which can be a source of diagnostic confusion.
1:33 Inter-Nodular Cellularity: The space between the nodules is filled with cellular material—primitive, bland, round-to-spindle cells (1:40).
2:22 Hemangiopericytic Features: These cellular areas contain dilated, branching vessels, often showing a "staghorn" or hemangiopericytic pattern. The speaker notes that the historical diagnosis of infantile hemangiopericytoma is now understood to be an exuberant form of Myofibroma (2:33).
2:55 Benign Behavior: Myofibromas are generally completely benign, rarely recur even when partially removed, and can sometimes spontaneously regress (3:05).
3:10 Clinical Presentation: While most well-known in children (where they can be multifocal), they can also be solitary lesions found in adults or even elderly patients (3:30).
3:15 Serious Pediatric Cases: Multifocal cases in babies, especially when involving internal organs, can be serious or fatal despite the tumor's benign nature.
3:55 Differential Diagnosis (Plexiform Neurofibroma): Myofibroma’s multi-nodularity is highlighted as the reason it is often confused with plexiform neurofibroma, although true plexiform lesions have an infiltrating, "bag of worms" appearance.
5:55 Second Example: A second example confirms the diagnosis but shows a less strikingly biphasic appearance, with smaller, more poorly formed nodules, yet maintaining the characteristic branching/staghorn vessel growth (6:25).
6:58 Distinction from Myopericytoma: Myofibroma and Myopericytoma are related and both typically benign. Myopericytoma is generally composed entirely of cellular pericytes with a whirling growth pattern and lacks the hypocellular myoid nodules that define Myofibroma (7:38).