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The interpretation of dermatopathology specimens can be confounded by artifacts unrelated to the primary pathology. Before making a histopathological diagnosis, tissue specimens must undergo a series of steps in preparation for microscopic examination. When errors occur in any stage of the tissue preparation process, artifact introduction to tissue specimens may result. Tissue artifact refers to an artificial structure on a microscopic slide resulting from an extraneous factor.[1][2] Many artifacts in dermatopathology specimens are present before tissue removal from the patient. Artifacts in tissue specimens can make interpretation difficult, especially if the pathologist is unfamiliar with the underlying etiology. Clinically, artifacts can be the primary reason for a biopsy, as in the case of a graphite tattoo.[3] Both clinicians and pathologists should be aware of potential artifacts in tissue specimens, the etiology of the artifacts, and if the artifact is related to the primary pathology.

Prefixation Artifacts Hemorrhage Hemorrhage of erythrocytes into surrounding tissue is a finding in some tissue specimens. Bleeding can be related to the underlying pathology, as seen in solar purpura. Hemorrhage artifact refers to extravasated erythrocytes that occur during the procedure and have no relation to the underlying pathology. (see Image. Histology Slide Hemorrhage) Thermal/Heat Thermal or heat artifacts are common in specimens where the provider utilizes excessive heat via laser or electrosurgery. The characteristic epidermal changes include loss of polarity of the epidermis, spindled keratinocytes, and, in extreme cases, epidermal necrosis with separation from the underlying basement membrane.[8] When deeper tissues are exposed to excessive heat, similar findings can occur, but the tissue may also take on more of an opaque or amorphous appearance.[9] (see Images. Histology Collagen and Histology Collagen Folds) Freeze Artifact In dermatopathology, freeze or ice artifacts are commonly encountered in the setting of frozen specimens utilized in Mohs micrographic surgery. Freeze artifacts can also be found in tissue frozen with liquid nitrogen before removal. The characteristic finding is vacuolated keratinocytes in the epidermis, but other findings include splaying of dermal collagen and loss of cell architecture.[10] (see Image. Vacuolar Change) Suture Surgeons may place sutures as a marker for orientation during the grossing process of the tissue specimen. Sutures can also be encountered at previous biopsy sites that were subsequently excised. The appearance of the suture will depend on the composition of the suture placed. Polyfilament sutures often appear as numerous round structures filling a lumen and are often birefringent when polarized.[10] (see Images. Polyfilament Suture and Suture Birefringence.) Injected Material Tissue samples may have injectable substances, such as intralesional corticosteroids. Intralesional corticosteroid is a common finding in keloids. The steroid may resemble light blue pools of mucin with occasional granulomatous inflammation.[11] Histologic findings are similar regardless of the type of corticosteroid injected and the steroid dosage.[12] (see Image. Corticosteroid Keloid) Aluminum Chloride

Tissue samples may have injectable substances, such as intralesional corticosteroids. Intralesional corticosteroid is a common finding in keloids. The steroid may resemble light blue pools of mucin with occasional granulomatous inflammation.[11] Histologic findings are similar regardless of the type of corticosteroid injected and the steroid dosage.[12] (see Image. Corticosteroid Keloid) Aluminum Chloride Aluminum chloride is used as an antiperspirant and hemostatic agent. Aluminum chloride is commonly encountered in dermatopathology excision specimens when used as a hemostatic agent at a prior biopsy site. The aluminum particles are seen within histiocytes with a granular cytoplasm. Aluminum chloride can also result in basophilic collagen alteration.[13][14] Granular deposition of aluminum chloride is a potential pitfall for considering other causes of parasitized histiocytes.[13] Ferrous Subsulfate (Monsel's solution) Ferrous subsulfate is sometimes used as a hemostatic agent and is also commonly encountered at previous biopsy sites in excision specimens. Ferrous subsulfate will appear as prominent pigmented deposits that are granular or more diffuse and "smudgy." The pigment may be found in macrophages, fibroblasts, or around collagen bundles.[15] If unfamiliar with this solution, distinguishing the pigmented ferrous subsulfate deposits from hemosiderin or melanin can be difficult.[14][15] (see Image. Ferrous Subsulfate) Gelfoam Gelfoam is sometimes used as a hemostatic agent and placed after a punch biopsy. Excision of the prior biopsy site will reveal the striking nature of the gelfoam. Gelfoam appears as distorted spaces surrounded by basophilic gelatin walls.[16] (see Image. Gelfoam) Tattoo Pigment Tattoo pigment may be found in dermatopathology specimens as a part of the primary pathology, as in granulomatous tattoo reactions. Tattoo pigment can also be an artifact or incidental finding unrelated to the primary pathology, such as in the background of skin cancer. Tattoo pigment is often found around the superficial dermal plexus but can sometimes be found with macrophages or between collagen bundles.[17] (see Image. Tattoo Pigment) Other Prefixation Artifacts Many other potential prefixation artifacts can be found in tissue related or unrelated to the primary pathology. The list is not exhaustive and includes injectable fillers, glass, metals, and many other substances.

Tattoo pigment may be found in dermatopathology specimens as a part of the primary pathology, as in granulomatous tattoo reactions. Tattoo pigment can also be an artifact or incidental finding unrelated to the primary pathology, such as in the background of skin cancer. Tattoo pigment is often found around the superficial dermal plexus but can sometimes be found with macrophages or between collagen bundles.[17] (see Image. Tattoo Pigment) Other Prefixation Artifacts Many other potential prefixation artifacts can be found in tissue related or unrelated to the primary pathology. The list is not exhaustive and includes injectable fillers, glass, metals, and many other substances. Fixation Artifacts Incomplete Fixation Ideally, tissue is fixed in an appropriate solution immediately upon removal from the patient to prevent any significant tissue alterations or protein degradation. Delay in fixation is not typically an issue in dermatopathology, but increased demand for turnaround time could lead to a decrease in total fixation time. If the tissue specimen is placed in an inadequate volume of formalin or not given enough time in formalin, tissue microtomy is compromised.[18] (see Image. Poorly-Fixed Specimen) Microwave Fixation Artifact Microwave fixation aids in the speed of tissue fixation, but the process can result in tissue texture alteration, tissue shrinkage, and breakdown of erythrocytes.[6] Microwave-induced tissue artifacts appear as increased vacuolization of cells, overstaining of cytoplasm, or pyknotic nuclei.[2] Improper Fixation (Saline) The storage of a tissue specimen in an improper fixative, such as saline for transport or as a temporary medium, can result in vacuolization of the basal layer epithelium, widespread vacuolization of cells, and eventually lysis of cells. The dermis displays the separation of collagen and eventual lysis of cell architecture.[19] Processing Artifacts Embedding During the embedding and microtomy process, if the tissue specimen is not aligned correctly, the specimen can be cut at an unfavorable angle. Improper embedding can lead to deeper connective tissue of the dermis appearing in the same plane as the epidermis. The result can give an appearance similar to an invasive squamous cell carcinoma.[2] Chatter/Venetian Blind Artifact

During the embedding and microtomy process, if the tissue specimen is not aligned correctly, the specimen can be cut at an unfavorable angle. Improper embedding can lead to deeper connective tissue of the dermis appearing in the same plane as the epidermis. The result can give an appearance similar to an invasive squamous cell carcinoma.[2] Chatter/Venetian Blind Artifact Chatter, also commonly referred to as Venetian blind artifact, is multiple parallel bands of tissue separated by narrow clear spaces that are said to resemble Venetian blinds.[20] The introduction of chatter artifact is often the result of the vibration of the specimen in the paraffin block during the operation of the microtome knife, especially if the blade is not tightly screwed down into its mount. Chatter artifact is also more common in certain conditions where nodular aggregates of inflammatory or neoplastic cells replace the stromal support within the dermis typically provided by collagen.[20] Floater Tissue floater artifact refers to tissue specimens contaminated by pathology from extraneous tissue. The classic example of a floater artifact in dermatopathology is a piece of basal cell carcinoma contaminating an unrelated tissue specimen, leading to a diagnostic dilemma. Although the grossing process can induce tissue floaters, the most common cause of tissue floater introduction is contamination of the water bath.[21] (see Image. Floater Artifact) Tissue Folds Tissue folds are among the most common artifacts encountered in daily practice. Tissue folds, or wrinkles, occur when thin sections fold over on themselves when placed onto the slide.[22] Tissue folds appear as darker stained sections due to the folded tissue being thicker and retaining more of the stain.[2] (see Image. Tissue Fold) Tissue Scores/Tears Tissue scoring artifact refers to a tissue tear extending linearly across the specimen.[2] The artifact results from imperfections in the microtome knife edge or "nicks" in the microtome blade. This artifact can result when sectioning hard material such as calcium.[2] (see Image. Tissue Tear) Crush Artifact Crush artifact refers to clusters of cells, often "small blue cells," with cellular details blending to become unrecognizable. Nuclei are less sensitive to crush artifacts and often appear stacked with distorted chromatin.[23] Mounting Artifacts

Tissue scoring artifact refers to a tissue tear extending linearly across the specimen.[2] The artifact results from imperfections in the microtome knife edge or "nicks" in the microtome blade. This artifact can result when sectioning hard material such as calcium.[2] (see Image. Tissue Tear) Crush Artifact Crush artifact refers to clusters of cells, often "small blue cells," with cellular details blending to become unrecognizable. Nuclei are less sensitive to crush artifacts and often appear stacked with distorted chromatin.[23] Mounting Artifacts Even while mounting the coverslip to the slide, there is potential for the insertion of artifacts. Air bubble entrapment can occur between the slide and coverslip.[9] Artifacts can also occur if a coverslip is mounted to a dry specimen or the mounting media peels away from the coverslip. Improper mounting can give a brown appearance over the areas where the coverslip is peeling away from the slide, making interpretation difficult. Distinguishing features of the specimen can be impossible to discern depending on the degree of artifact. (see Image. Improper Mounting)