The Lunula: A Magnetic Resonance Imaging Approach to the Subnail Matrix Area

Abstract

High-resolution sagittal magnetic resonance images depict an oval area in the dermis beneath the nail matrix that gives a particular signal. This study defines the magnetic resonance imaging characteristics of this area and examines its correlation with the lunula. A high-resolution surface gradient coil specially designed for skin imagining was used on a 1.5 T magnetic resonance unit. The subnail matrix (SNM) areas of 12 subjects had a significantly longer T2 relaxation time and a higher enhancement ratio after injection of gadolinium than did the nail bed dermis. The length of the SNM area distal to the free edge of the proximal nail fold was highly correlated with the length of the lunula (R = 0.98) in 30 fingers and 10 toes. The total length of the SNM area was somewhat correlated with the nail thickness (R = 0.86) in 30 fingers. The histology and microvascularization of the subungual tissue in 21 fingers showed that this SNM area had specific features: The area was composed of loose connective tissue without bundles, and the reticular and subdermal vascular networks had large regular meshes in this oval area. The lunula is shown to be linked to a well-defined area in the underlying dermis with a specific histology and microvascularization.

Advances in MR imaging of the skin

“…In addition to relaxation times, MT ratios and the ADC, other parameters could be used to study skin physiology. For example, the ability of MR imaging to detect flow in very small vessels (40,41) could provide information on skin vascularization in normal and pathologic conditions. Multiple quantum-filtered images, the contrast of which depends on the coupling of water and macromolecules (42) such as skin collagen, could provide more new information on the water status of the body's largest organ.…”

Feasibility study of 3-T MR imaging of the skin

“…MRI could also be useful for exploring nail beds and their pathology. All in all, this area is difficult to study clinically, and MRI could provide additional information such as precise localisation, extension and even lesion characterisation [20,21].…”

Importance of visible lunula in healthy and diseased fingernail plates

“…As the thumbnail plate is the largest one (length and width), and the dermis of the lunula region acts as a sliding system; 5 we suggest that a large sized nail must be formed from a large matrix that leads to forward extension of the distal matrix as visible lunula. A small sized nail must be formed from a small matrix with limited extension and invisible lunula.…”