This pathology review focuses on the diagnosis and characteristics of Nodular Fasciitis (NF) based on microscopic examination of a tissue sample. The speaker highlights key histological features, emphasizing the presence of spindle cell proliferation within a loose, myxoid background, often interspersed with keloidal collagen bundles. The most diagnostic feature cited is the presence of "myxoid cystic degeneration"—pockets where cells have separated, leaving empty space. Although NF was historically viewed as a reactive process following trauma, it is now understood to have a genetic translocation, classifying it as a self-limited, benign neoplasm. The speaker discusses the cellular morphology (plump spindle cells or stellate cells) and notes that immunohistochemical staining for smooth muscle actin often reveals a characteristic "tram track" pattern along the cell membranes, though staining is often unnecessary for diagnosis when the classic features are present on H&E stain. Clinical context is provided: lesions are typically fast-growing, painful, usually found in young adults/children, and most importantly, usually small (under 3 cm); larger lesions warrant further differential consideration (e.g., sarcomas).
Microscopic Diagnosis of Nodular Fasciitis
0:00 Subcutaneous Nodule: Examination of a deep subcutaneous nodule, potentially attached to fascia, showing wavy connective tissue indicative of fascia/tendon.
0:00 Spindle Cell Proliferation: The lesion is characterized by proliferating spindle cells in a loose myxoid background, sometimes forming small fascicles.
0:42 Key Diagnostic Feature: The most helpful feature for diagnosing Nodular Fasciitis (NF) is the presence of myxoid cystic degeneration (pockets where cells separate, leaving empty space).
1:05 Lesion Aging: Early lesions are more cellular with mitotic activity; older lesions show more breakdown, increased cystic change, and sclerotic collagen.
1:29 Cell Type: The cells are myofibroblasts, morphologically similar to those in granulation tissue.
1:59 Neoplastic Nature: NF is now recognized as a self-limited, benign neoplasm due to a discovered translocation, despite often arising after trauma.
2:37 Cytology: Cells are plump spindle cells or stellate (star-shaped/triangular) cells; mitotic activity is common but pleomorphism is absent.
3:21 Smooth Muscle Actin Stain: Staining for SMA often reveals a "tram track pattern" highlighting the cell periphery, common in myofibroblastic lesions.
3:47 Diagnostic Strategy: The speaker typically diagnoses NF solely on H&E stain and rarely uses additional stains or molecular workup unless the case is difficult or a partial biopsy is received.
4:09 Terminology: The loose appearance of stellate cells in a myxoid background is sometimes termed "tissue culture" by some pathologists, but the speaker prefers "loose and feathery."
4:42 Inflammation: Despite the "-itis" suffix, inflammation is not required for a diagnosis of NF.
4:53 Clinical Presentation: Lesions typically grow quickly, are painful, often affect extremities of young adults/children, and are usually small (under 3 cm).
5:11 Caution on Size: Lesions exceeding 3 cm raise suspicion that the diagnosis might be a more aggressive process (like sarcoma) rather than NF.
5:44 Growth Patterns: NF usually presents as a nodule but can occasionally grow linearly along the fascia.
6:00 Prognosis: NF is totally benign and usually does not recur, even if excised with positive margins.