Use of double-bladed biopsy in distinguishing keratoacanthoma from squamous cell carcinoma—a case report

“The SCC Biopsy Tool” (name provided by current authors) is a double-bladed scalpel handle (manufactured and distributed by Surgidental Instruments, Deer Park, NY, USA) with two No. 11 scalpel blades (Swann-Morton, Sheffield, England) set in parallel, 1.5 mm apart (Figure 1). It provides an alternative to other partial biopsy methods and provides advantages over established techniques of shave and punch biopsy, particularly in differentiating squamous cell carcinoma (SCC) from keratoacanthoma (KA) on the leg and foot. The method of obtaining a full-thickness sample across the total width of a lesion with histologic sectioning in a longitudinal plane enables both architecture and cytology to be assessed accurately; precisely the requirement for distinguishing SCC from KA. The advantage over traditional incisional biopsy with a single blade is precision of parallel edges in a situation where central keratin provides an obstacle to such precision.

"The SCC Biopsy Tool" (name provided by current authors) is a double-bladed scalpel handle (manufactured and distributed by Surgidental Instruments, Deer Park, NY, USA) with two No. 11 scalpel blades (Swann-Morton, Sheffield, England) set in parallel, 1.5 mm apart ( Figure 1). It provides an alternative to other partial biopsy methods and provides advantages over established techniques of shave and punch biopsy, particularly in differentiating squamous cell carcinoma (SCC) from keratoacanthoma (KA) on the leg and foot. The method of obtaining a full-thickness sample across the total width of a lesion with histologic sectioning in a longitudinal plane enables both architecture and cytology to be assessed accurately; precisely the requirement for distinguishing SCC from KA. The advantage over traditional incisional biopsy with a single blade is precision of parallel edges in a situation where central keratin provides an obstacle to such precision.

Case report
A 94-year-old lady presented with a rapidly growing, nonpigmented nodular lesion on the lateral side of the right foot ( Figure 2). Clinically there was central keratin, as can be seen in both KA and SCC. The symmetry of the lesion was consistent with KA but it was tender to palpation, a feature commonly regarded as a clue to SCC. At approximately 2 mm in thickness it was at the threshold of metastatic potential if it was to be an SCC [13].
Dermatoscopic assessment revealed central structureless white (keratin) with blood spots. It has been shown that KA cannot be reliably distinguished from SCC with dermatoscopy [9], and certainly in this case dermatoscopy did not clarify the differential diagnosis.
The lesion was 13 mm in diameter, in which case excisional biopsy with 1 mm margins would have created a defect 15 mm in diameter, and it was assessed that primary closure While KA is often suspected clinically due to the features of a rapidly appearing and growing raised, non-pigmented lesion with a central keratin plug, SCC can also have this appearance. Furthermore, cases of KA with SCC arising from the base have been reported [8]. It has been shown that SCC and KA cannot be reliably distinguished dermatoscopically [9]. Whether KA is a form of SCC with benign, non-metastasizing behavior [10] or, as the current authors believe, a distinct, benign histologic entity [11], we believe that the differentiation is of practical significance. While it is regarded as appropriate to treat KA rather than to monitor them, it is also accepted that the majority of KA have a good prognosis with conservative treatment [12].
We propose that, because of the potential for increased morbidity with complex surgery on the leg and foot, histologically confirmed KA on these locations can be monitored for a limited time in anticipation of resolution and subsequently excised if this does not occur. Due to the properties of skin of the leg and foot, excisional biopsy at these locations may require a complex closure with a significant risk of flap or graft failure, and for this reason we believe an effective but minimally invasive biopsy method is desirable.
The case presented here illustrates such a biopsy method. It provides a biopsy specimen through the center of a suspect lesion, which provides the dermatopathologist with information on both cytology and architecture through the entire central cross section and depth of the lesion. Since the tissue removed is only 1.5 mm in width, the defect can easily be closed even in very tight tissue, such as in cases of lipodermatosclerosis, and in more pliant tissue, closure can usually be achieved simply with Steristrips. If the lesion is a KA, we believe this can be confirmed with a high degree of confidence. The KA can then be observed for anticipated resolution. We have also observed anecdotally that regression often follows immediately after the act of biopsy, although we have   [14].
In this case, the assessment was made that even a defect created by a 4 mm punch biopsy might not be able to be closed without excessive skin tension.  [14,15]. There was no superimposed SCC, as is seen would not be possible. An experienced dermatopathologist would be able to diagnose KA on a punch biopsy from the unique histologic characteristics of KA because the cells in a KA have a distinct hue in their cytoplasm that is paler than that seen in SCC, best visualized in the large central cells in the squamous nests which may be up to double the size of the peripheral cells [14,15]. These central pale cells of KA tend to be much larger than the cells of SCC [14,15]. The diagnosis of KA from a punch biopsy may not detect SCC arising in the base, which has been shown to occur in 5-13% of KA [8]. To diagnose KA with more confidence, most pathologists would also prefer to see the architecture of the squa-   A B in at least 10% of KA in patients of this age [8]. On the basis of this report the decision was made not to immediately proceed to formal excision and complex closure but to observe for up to two months in anticipation of resolution. The lesion had clinically regressed completely when reviewed two months after the biopsy procedure. We believe that this was a favorable course of action for the patient, who, at the age of 94, was agreeable to avoiding any potentially unnecessary procedure.

Warning
Mounting blades on a double-bladed scalpel is technically more difficult than with conventional scalpels. The authors advise physicians and/or support staff to perform this task with care.

Conclusion
The double bladed scalpel with blades 1.5 mm apart has been shown in this case report to have utility as an "SCC biopsy tool." It enabled an optimum dermatopathologic assessment to distinguish KA from the differential diagnosis of SCC. An immediate formal excision with associated complex closure was avoided in a 94-year-old patient. We believe the double-bladed scalpel, used as described in this report, is a useful tool especially for lesions on the leg and foot when it is desirable to differentiate KA from SCC and to minimize surgical trauma.