Letter to the Editors

Slit creation is one of the most important steps in a hair transplant. The recipient site creation process is an art and ultimately decides the impact of the result. The process of slit making is described in two terms: the sequence of slit making and the orientation of slits. In terms of sequence, slits are described as premade and “stick and place.” In terms of slit orientation, they are described as sagittal and coronal.1,2 These terms are primarily used in describing the orientation and only occasionally, and often parenthetically, are parallel and perpendicular used. It is our contention that in terms of what is practically done, the terms sagittal and coronal are often inaccurate. We propose that the terms parallel and perpendicular are more explanatory of the orientation and should be primarily used in communicating slit orientation. A sagittal plane is defined as one that divides the body into left and right sections. A coronal plane is one that divides the body into a dorsal (back) and ventral (front) section. If these definitions are strictly followed in the process of slit making, all sagittal slits would have hairs directed straight anteriorly with no angulation to the left or right. All coronal slits would have hairs directed left or right with no angulation to the front or back (Figure 1). However, as we know, this is not how slits are usually made. Slits are typically made in orientation to the existing hair pattern. Sagittal slits are usually made parallel to the hair direction, with the result that these so-called “sagittal” slits actually end up becoming almost coronal laterally in the temporal peak. Coronal slits are usually made perpendicular to the hair direction, and these slits become near sagittal in the temporal region. These definitions thus hold true only in the center of the scalp. These definitions become even more problematic and untenable when it comes to the vertex, where they are made in a circular manner following the whorl pattern of the hairs. Hence, the current description is inaccurate in many areas of the scalp, and we would like to propose the use of nomenclature that we believe more accurately depicts what is routinely followed in practice. What is commonly called “sagittal” actually refers to slits that are made parallel to the direction of the hair. Hence, we believe these slits should be called PARALLEL slits. What is commonly called “coronal” actually refers to slits that are made perpendicular to the direction of the hair. Hence, we believe these slits should be called PERPENDICULAR slits (Figure 2). There are important implications of the nomenclature. First, this nomenclature places emphasis on the orientation of the slit with regard to the direction of the hair being implanted. Hence, a parallel or perpendicular slit can be made in any direction: frontal, back, left, or right. This nomenclature, therefore, holds its meaning in all areas, even in the temporal and vertex regions. While we initially believed we were the first to coin this term, we found an earlier paper by Jerry Wong in 2002 suggesting the use of the term perpendicular slits in the temporal region. The author stated: “Although it is labeled coronal incisions, it is actually the direction of hair flow that determines the incisional plane. Because the incisional plane is always 90° to the directional of hair flow, perpendicular incisions may be a more accurate description.”3 However, this term did not gain popularity as this paper was focused on comparing slits in the temporal region only and did not lay out the logical fallacy of these terms completely. Since then, the terms parallel and perpendicular have been used but usually secondarily and often in parenthesis behind the primary terms being used, sagittal and coronal. Second, as a parallel slit is along the hair direction, the length of the slit at the surface increases as the angle of the hair decreases. However, when the slit is perpendicular to the hair direction, the length at the surface of the slit does not change with angulation. This allows smaller size of slits, more dense packing, and less popping. This concept has been described before with mathematical elucidation.4,5 To summarise, the terms parallel and perpendicular are more explanatory of the slit arrangement and direction in all scalp locations and should replace the existing terms sagittal and coronal. We hope that this letter sparks conversation and helps correct longstanding misnomers in hair transplant terminology. We also hope the new terminology is adopted to ensure accurate anatomical description and reporting of the slit-making process. FIGURE 1. Sagittal and coronal slits FIGURE 2. Parallel and perpendicular slits