‘Venetian blinds’ artifact in dermatohistopathology

Abstract

The ‘Venetian blinds’ artifact is an uncommon tissue cutting artifact that leads to the formation of parallel series of strips of tissue separated from one another by narrow clear spaces. It has been attributed to either hardening of the tissue in the paraffin block or defective assembly of the microtome knife. This artifact occurs in both inflammatory and neoplastic conditions in which there are nodular collections of cells and may reflect vibration-induced disintegration of fragile cellular aggregates that lack dermal stromal support. At scanning magnification, it serves to draw the histopathologist's eye to the site of pathology.

INTRODUCTION

The ‘Venetian blinds’ artifact is an uncommon tissue cutting artifact that leads to the formation of parallel series of strips of tissue separated by narrow clear spaces that resemble Venetian blinds. This artifact has been attributed to vibration of the specimen in the paraffin block, caused either by excessive hardening of the tissue in it or by improper maintenance and consequent defective operation of the microtome knife assembly during the process of cutting.[1]

A few articles have described the ‘Venetian blinds artifact’ in histopathology;[2,3] however, in dermatopathology there is a dearth of articles on this artifact which may be seen in several neoplastic and inflammatory diseases.

In this article, we describe the Venetian blinds artifact in neoplastic, granulomatous, and infective conditions and hypothesize the causes for this distinctive artifact.

REPORT OF CASES SHOWING THE VENETIAN BLINDS ARTIFACT

Case 1 is non-Hodgkins lymphoma that shows diffuse dermal infiltration by atypical lymphocytes [Figure 1]. At the upper right hand corner of the sections are seen oblique knife marks while in the lower left and central part the nodular lymphocytic infiltrate is broken up into parallel strips giving rise to the Venetian blinds artifact [Figures 2 and 3].

Figure 1.

Low power view of NHL, showing diffuse dermal infiltration by lymphoid cells, knife marks at the upper right corner, Venetian blinds effect in the lower central and left areas (H and E, ×40)

Figure 2.

Medium power view showing Venetian blinds artifact in the nodular collection of neoplastic lymphoid cells (H and E, ×100)

Figure 3.

High power view with parallel strips of tissue containing atypical cells, irregularly broken up, with clear spaces between adjacent strips of tissue (H and E, ×400)

Case 2 depicts the Venetian blinds artifact in lupus vulgaris, involving a large epithelioid cell granuloma with many large Langhan's giant cells. The granuloma is seen in the upper dermis and hugs the overlying epidermis. The granuloma and the individual giant cells are broken up into parallel strips of tissue made up of cytoplasm of epithelioid histiocytes [Figures 4 and 5].

Figure 4.

Lupus vulgaris with a large epithelioid cell granuloma in the upper dermis with many Langhan's type giant cells (H and E, ×100)

Figure 5.

High power showing Venetian blinds artifact involving the giant cells (H and E, ×400)

Case 3 is actinomycetoma, with suppurative nodules in the dermis consisting of collections of neutrophils surrounded by histiocytes. Two such suppurative nodules contain in the centre, ‘grains’ made up of basophilic, finely filamentous organisms [Figure 6]. At higher power, the actinomycotic ‘grain’ is seen to be split up into parallel strips with clear spaces in between, and is surrounded by many neutrophils and few histiocytes and foreign body giant cells [Figure 7].

Figure 6.

Scanning power showing suppurative nodules in the dermis with two actinomycotic grains (H and E, ×25)

Figure 7.

High power of grain showing artifact, with surrounding neutrophils, histiocytes, and foreign body type giant cells (H and E, ×400)

DISCUSSION

It has been suggested that the Venetian blinds artifact (also referred to as the ‘chattering’ or ‘stuttering’ of the knife) occurs due to vibration of the specimen in the paraffin block and can be corrected if the microtome knife assembly is optimally maintained. The knife holder, all adjusting screws, and other components of the mechanism that hold the paraffin block, must be checked regularly and tightened properly.[1]

It is an artifact causing tissue damage, and cuts across nuclei and other cellular structures without following normal tissue planes. It is often accompanied in the same tissue sections by knife marks that indicate a blunt cutting edge of the microtome knife.

Diseases where this artifact occurs have as their cardinal histological presentation nodular collections of cells, either inflammatory or neoplastic with the cells replacing the surrounding fibrous stroma. The lack of stromal support, normally afforded by collagen in the dermis may be an important factor in vibration-induced fragmentation of the fragile collection of cells of the neoplasm or granuloma.

Interestingly, while this artifact has been seen in actinomycotic ‘grains’, we have not observed it in eumycotic ‘grains’, owing probably to the structural support that the large hyphae of eumycetes lend the eumycotic ‘grain’.

Apart from the cases described above, we have seen the Venetian blinds artifact in epithelial malignancies (Basal cell carcinoma, squamous cell carcinoma), other granulomatous conditions (Borderline tuberculoid Hansens) and even in the epidermis adjacent to granulomas.

At scanning magnification, this distinctive artifact serves to draw the histopathologist's eye to the site of pathology, namely, collection of cells either neoplastic or inflammatory, and serves to remind histotechnicians to check and optimally tighten microtome blade holder screws to prevent vibration of the knife as it cuts through the tissue.