Key points

Introduction

Laboratory technicians and pathologists often fear receiving a nail unit specimen because there are significant challenges in both getting the nail plate to adhere to a glass slide and because the soft tissue specimens of the nail unit matrix and bed are often small and fragmented. Interpretation by the pathologist is challenging, not only because of the often difficult nature of the specimen but also because orientation at the microscopic level is tricky, especially when examining a diseased nail unit.

When routine skin specimens are obtained in a clinic, the specimens are usually placed free floating in a container with an appropriate amount of formalin (10% formaldehyde) before the specimen is sent to the laboratory. With nail unit specimens, however, placing these specimens free in formaldehyde results in loss of orientation and frequent loss of critical tissue needed to make a diagnosis. Maintenance of tissue integrity and orientation streamlines specimen processing—from grossing to embedding to sectioning—and significantly improves pathologic diagnostic ability. Thus, in the clinic, nail unit specimens require additional work to preserve tissue integrity and orientation.

It is helpful to be able to send nail unit specimens to a laboratory with expertise in nail specimen processing. However, the clinic is often required to send to a variety of laboratories. By preparing a nail unit specimen in the clinic in a way that preserves orientation and prevents loss of tissue, the specimen may thus be processed and interpreted in a variety of laboratories with better success. Thus, the onus is on the clinician and the clinic to submit nail specimens in a manner as discussed later.

Clear communication with the laboratory is important in nail unit specimen submission. Of primary importance is instruction to the laboratory to pay close attention to small fragments of tissue. Instructions to perform initial level sections and unstained sections on positively charged slides are important because the small nail matrix/bed specimens may not survive refacing the paraffin block for additional sections. Also important is a clear clinical history and differential, especially because the histologic features of some nail tumors such as onychopapilloma are not distinct. A pathologist not given a clear differential will diagnose an onychopapilloma as a verruca, as both have hyperkeratosis and hypergranulosis. Similarly, a diagnosis of a mold infection requires direction by the clinician to the laboratory to consider a mold; otherwise, the microbiology laboratory will consider the mold a contaminant and not characterize the mold.

For submission in a way that preserves specimen orientation, a couple of methods have previously been proposed. George and colleagues describe a technique of marking the epithelial surface with colored ink, dipping the specimen in glacial acetic acid to fix the ink, and then placing it in formalin for transport. Although this technique may certainly improve orientation by maintaining the ability to identify the epithelial surface, placing the specimen floating free in formalin will lead to a loss of proximal-distal and medial-lateral orientation, and small fragments of potentially diagnostic tissue may be lost. Richert and colleagues describe a different technique for submission in which the specimen is placed on cardboard with a nail diagram and covered with a sheet of filter paper. The cardboard and filter paper are then stapled together so that the specimen remains flat and oriented, preventing tissue loss.

Introduction

Laboratory technicians and pathologists often fear receiving a nail unit specimen because there are significant challenges in both getting the nail plate to adhere to a glass slide and because the soft tissue specimens of the nail unit matrix and bed are often small and fragmented. Interpretation by the pathologist is challenging, not only because of the often difficult nature of the specimen but also because orientation at the microscopic level is tricky, especially when examining a diseased nail unit.

When routine skin specimens are obtained in a clinic, the specimens are usually placed free floating in a container with an appropriate amount of formalin (10% formaldehyde) before the specimen is sent to the laboratory. With nail unit specimens, however, placing these specimens free in formaldehyde results in loss of orientation and frequent loss of critical tissue needed to make a diagnosis. Maintenance of tissue integrity and orientation streamlines specimen processing—from grossing to embedding to sectioning—and significantly improves pathologic diagnostic ability. Thus, in the clinic, nail unit specimens require additional work to preserve tissue integrity and orientation.

It is helpful to be able to send nail unit specimens to a laboratory with expertise in nail specimen processing. However, the clinic is often required to send to a variety of laboratories. By preparing a nail unit specimen in the clinic in a way that preserves orientation and prevents loss of tissue, the specimen may thus be processed and interpreted in a variety of laboratories with better success. Thus, the onus is on the clinician and the clinic to submit nail specimens in a manner as discussed later.

Clear communication with the laboratory is important in nail unit specimen submission. Of primary importance is instruction to the laboratory to pay close attention to small fragments of tissue. Instructions to perform initial level sections and unstained sections on positively charged slides are important because the small nail matrix/bed specimens may not survive refacing the paraffin block for additional sections. Also important is a clear clinical history and differential, especially because the histologic features of some nail tumors such as onychopapilloma are not distinct. A pathologist not given a clear differential will diagnose an onychopapilloma as a verruca, as both have hyperkeratosis and hypergranulosis. Similarly, a diagnosis of a mold infection requires direction by the clinician to the laboratory to consider a mold; otherwise, the microbiology laboratory will consider the mold a contaminant and not characterize the mold.

For submission in a way that preserves specimen orientation, a couple of methods have previously been proposed. George and colleagues describe a technique of marking the epithelial surface with colored ink, dipping the specimen in glacial acetic acid to fix the ink, and then placing it in formalin for transport. Although this technique may certainly improve orientation by maintaining the ability to identify the epithelial surface, placing the specimen floating free in formalin will lead to a loss of proximal-distal and medial-lateral orientation, and small fragments of potentially diagnostic tissue may be lost. Richert and colleagues describe a different technique for submission in which the specimen is placed on cardboard with a nail diagram and covered with a sheet of filter paper. The cardboard and filter paper are then stapled together so that the specimen remains flat and oriented, preventing tissue loss.