This video discusses the diagnostic challenges and differentiating features between two benign melanocytic lesions: cellular blue nevus (CBN) and deep penetrating nevus (DPN). Dr. Jared Gardner and Dr. Edward Fulton highlight that despite their often "atypical" appearance – including hypercellularity, deep dermal/subcutaneous extension, larger nuclei, and occasional mitotic activity – both entities are benign and should not be misdiagnosed as melanoma.
The video details the characteristic "dumbbell" architecture of CBN, often presenting with peripheral areas resembling conventional blue nevi and sometimes hypopigmentation. DPN, in contrast, typically exhibits a "wedge" or "upside-down pyramid" shape, with melanocytes showing abundant pale pink-to-gray cytoplasm, prominent nucleoli (Spitzoid features), and a tendency to track along adnexal structures. Differential diagnoses, such as Clear Cell Sarcoma for CBN and Spitz Nevus for DPN, are explored, along with the utility of molecular studies for definitive diagnosis in ambiguous cases. The speakers emphasize a pragmatic diagnostic approach, prioritizing the benign versus malignant distinction based on overall architecture and context, and stress the importance of consultation for difficult cases due to inherent overlaps and the evolving understanding in melanocytic pathology.
Summarizing Cellular Blue Nevus (CBN) vs. Deep Penetrating Nevus (DPN):
0:00 Introduction to Challenging Diagnoses: The video focuses on differentiating Cellular Blue Nevus (CBN) and Deep Penetrating Nevus (DPN), two benign melanocytic lesions often confused due to overlapping features.
Key Takeaway: Despite their unusual appearance, both are benign, and the main goal is to avoid misdiagnosing them as melanoma.
Architecture: Often exhibits a "dumbbell pattern," pushing from the dermis into the subcutis.
Cellularity: Hypercellular centrally, with cellularity tending to decrease in the upper dermis.
Pigmentation: Can be hypopigmented, but scattered melanin (melanocytes and melanophages) is present.
Peripheral Clue: Frequently, areas resembling conventional blue nevus can be found at the periphery, which is a useful diagnostic indicator.
Cytology: Oval to spindle cells, packed in nodules, sheets, or elongated fascicles/nests.
Differential Diagnosis: Consider Clear Cell Sarcoma due to fascicular growth and cellularity; distinguishing features include nucleoli prominence and molecular testing.
Atypia & Mitoses: Scattered atypical cells (pleomorphism) and occasional mitotic activity are acceptable and do not indicate malignancy in an otherwise classic CBN.
8:43 Deep Penetrating Nevus (DPN) Characteristics:
Architecture: Typically has a "wedge shape" or "upside-down pyramid" pointing deep into the biopsy.
Cellularity: Melanocytes form elongated nests that intercalate with dermal collagen bundles.
Cytology: Cells generally have more abundant, pale pink-to-gray cytoplasm; nuclei are large, oval-to-round, with vesicular chromatin and prominent nucleoli (often described as "Spitzoid cytologic features").
Pigmentation: Abundant melanin deposition in background melanophages and dusty, grayish-brown melanin in melanocytes is common.
Adnexal Association: Tends to track along adnexal structures like eccrine ducts and hair follicles.
Differential Diagnosis: Molecular studies suggest overlap with Spitz Nevi.
11:01 Overlapping Features & Important Considerations:
Benign Nature: Both DPN and CBN are benign lesions despite features that might be worrisome in other contexts (e.g., deep penetration, cellularity, nuclear atypia, occasional mitoses).
Perineural Involvement: Melanocytes wrapping around nerves (perineural involvement) is a normal and acceptable growth pattern for benign nevi (including DPN and CBN) and should not be interpreted as perineural invasion or malignancy.
Maturation/Zonation: These lesions break the conventional rule of maturation where cells become smaller and less cellular deeper down; DPN and CBN can maintain high cellularity and cell size even at deep aspects.
Diagnostic Approach: Always start with low-power architecture before examining high-power cytology. Consider clinical context (patient age).
Combined Nevus: If classification is difficult, consider the possibility of a "combined nevus" with components of different nevus types.
Pragmatism: The most crucial distinction is between benign and malignant for patient care, even if specific sub-classification is challenging or subject to evolving definitions.
Consultation: For any doubt, especially with melanocytic lesions, seeking consultation from experienced colleagues is highly recommended.