Sir,

Despite increasing interest in the use of various imaging modalities such as ultrasound, magnetic resonance imaging, and positron-emission tomography, temporal artery biopsy remains the gold standard in the diagnosis of giant cell arteritis (GCA).1 Given that GCA can lead to profound irreversible blindness and other devastating complications, every effort must be made to ensure a correct diagnosis is made in each and every case.

Case report

We report a case of an 88-year-old patient referred with suspected GCA. A temporal artery biopsy was performed. Macroscopically, the specimen had a segmented, earthworm-like appearance. The 22-mm-long specimen was processed in toto and sectioned in the longitudinal plane at six levels, ∼120 μm apart. This demonstrated patchy focal inflammation, predominantly in the outer media, with ‘skip areas’ of 3–5 mm of uninflamed artery (Figure 1). The inflammatory infiltrate consisted predominantly of mixed mononuclear inflammatory cells (Figure 2). Had the artery been sectioned transversely alone, it is possible that the patchy inflammation would have been missed.

Figure 1
figure 1

Low magnification of longitudinal cross-section of TAB specimen demonstrating patchy areas of inflammation (arrowheads) with skip lesions of 3–5 mm of uninflamed artery.

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Figure 2
figure 2

Higher magnification showing inflammatory foci consisting of mononuclear inflammatory cells and a multinucleated histiocyte (‘giant cell’, marked by arrowhead).

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Simple geometrical calculation shows that the approximate area of a longitudinal section of artery is 2lr (where l is the length of the artery and r is its radius). The area of a transverse section is πr2. Where the entire artery is bread-loafed at intervals of about 3–4 mm, as is the standard textbook recommendation,2 then the total transverse area available for examination would be πr2l/3 (for transverse block length of 3 mm). Further calculation reveals that with an arterial transverse diameter of about 2.5 mm,3, 4 the area of tissue available for examination using longitudinal sections is about 50% greater than using transverse sections, and that difference doubles to the advantage of the longitudinal section if the transverse slices are 4 mm long. (The calculations are more complex in reality as we have not considered factors such as the diminishing areas obtained with deeper longitudinal sectioning and the influence of the variable size of the arterial lumen).

In the practical experience of one of the authors (AG) over several decades of practice, almost invariably, many of the transverse slices end up longer than 3–4 mm and the entire artery is not processed. Furthermore, any perceived advantage with transverse sectioning is on occasion lost owing to the difficulty of handling and orientating small pieces of tissue during processing. Despite the best intentions of the pathologist, this may result in many of the transverse pieces being actually embedded and sectioned in the longitudinal plane.

Comment

We therefore believe that longitudinal sectioning of the artery is a more appropriate strategy than transverse sectioning as it allows a greater proportion of the available specimen to be examined microscopically. That method of tissue handling is also considerably easier for laboratory staff to process.

To the best of our knowledge, there has been very little research into this area. A study presented at a conference in 2007 that examined 495 TAB specimens over a 15-year period reported that longitudinal sectioning yielded a 20% increase in positive biopsy results over transverse sectioning.5 However, to our knowledge these results were not published in the peer-reviewed literature.

It is important that all clinicians involved in the diagnosis and management of giant cell arteritis are aware of the issues of specimen length and sectioning strategy when evaluating the TAB result. We recommend surgeons discuss with their pathologist colleagues the sectioning strategy used to yield the most accurate result.