I usually post monthly, following a group teaching session, but this case is worth commenting on separately.
It was a routine specimen that arrived one Monday morning with clinical information of: endothelial cell failure, DMEK surgery.
We receive about a dozen corneal specimens per week, and there wasn’t anything of note macroscopically. Descemet’s membrane specimens can be difficult to locate in the specimen pot because they’re transparent, so we often add a drop of Alcian blue, which stains the tissue and aids visibility.
On microscopy, however, the appearance was like nothing I’d seen before.
This low power view shows a sheet of Descemet’s membrane with a conspicuous layer of cells on one surface.
For comparison, here’s a more typical Descemet’s membrane (pseudophakic bullous keratopathy) with only a couple of endothelial cells.
On higher power, the cells don’t resemble endothelium (or even epithelium) at all. They’re large, with bizarre spindled and stellate shapes, big nuclei and prominent nucleoli. There’s even a mitosis (marked with an asterisk)
The appearance was rather alarming, although in a research setting I might be thinking of fibroblasts in tissue culture. As a diagnostic histopathologist, my two immediate thoughts were: 1. Is this some tumour, perhaps even a sarcoma, metastatic to the aqueous? and 2. Maybe some odd viral infection?
Establishing either diagnosis would require more work, including immunohistochemistry, maybe asking a microbiology laboratory to attempt PCR on the small amount of tissue in the paraffin wax block. Potentially expensive and time-consuming.
Instead, we did a quick and simple test, described in this article.
If we add Schiff’s solution to neutral buffered formalin, it turns pink as in this series of photos. We’d added a drop of Alcian blue to this formalin, just for equivalence with our specimen.
However, with the specimen pot that contained our specimen, there was no pink reaction on addition of Schiff’s, demonstrating that the liquid the specimen arrived in wasn’t formalin.
We don’t know what liquid the specimen pot really contained. As we expect all tissue specimens to be submitted in formalin, we had no reason to suspect otherwise. But presumably over the weekend after surgery, the unfixed endothelial cells survived and multiplied, hence the odd appearance on microscopy.
Take home message? Please, surgeons, submit all histopathology specimens in formalin unless you have explicitly arranged otherwise with the laboratory.