Birthmarks are common skin markings present at birth or appearing shortly after. They vary widely in size, shape, and color, and are generally harmless. This article clarifies whether birthmarks are detectable through ultrasound.
Understanding Birthmarks
Birthmarks are categorized into two main types: pigmented and vascular. Pigmented birthmarks result from an overgrowth of melanocytes, the cells responsible for producing skin color. Examples include café-au-lait spots, which are flat, light brown patches, and moles (nevi), which can be flat or raised and vary in color. Mongolian spots are another type, appearing as bluish-gray patches, often on the buttocks or lower back, and are more common in individuals with darker skin tones.
Vascular birthmarks are caused by abnormally formed blood vessels, appearing as red, pink, purple, or blue patches or lumps on the skin. Common vascular birthmarks include hemangiomas, benign growths of blood vessels that often appear after birth and can grow rapidly before shrinking. Port-wine stains are flat, deep-red or purple marks made of dilated capillaries that are usually permanent. Most birthmarks, regardless of type, are superficial skin findings.
Ultrasound’s Visual Limitations
Ultrasound technology works by emitting high-frequency sound waves into the body, interpreting the echoes that return. These sound waves travel through tissues and reflect off different structures, creating an image based on their density and composition. This imaging method excels at visualizing organs, fluid-filled spaces, and deeper structures. However, birthmarks, whether pigmented or vascular, are superficial skin characteristics.
Ultrasound is not designed to capture surface details like skin color or pigmentation patterns. A café-au-lait spot is a discoloration on the outermost skin layer, which ultrasound waves pass over without significant reflection. Similarly, superficial vascular birthmarks like port-wine stains are too close to the surface and lack the depth or structural anomaly that ultrasound visualizes. Therefore, prenatal ultrasounds cannot detect these external skin markings.
Discoveries Possible Through Ultrasound
While superficial birthmarks are not visible on ultrasound, the technology can identify deeper or more complex conditions. Ultrasound is effective for assessing internal masses or structural anomalies, especially when they involve blood vessels. Large vascular malformations, extending beyond the skin’s surface into deeper tissues or organs, can be detected and characterized by ultrasound, often using color Doppler to assess blood flow. These are not merely skin discolorations but complex formations of abnormal blood vessels.
Ultrasound may also provide clues for conditions associated with birthmarks, particularly syndromes involving underlying structural issues. For instance, in ectodermal dysplasia, where skin and other ectodermal structures are abnormally developed, ultrasound might reveal related skeletal or dental anomalies. Such findings prompt further investigation, potentially including genetic testing, to confirm a diagnosis. This capability allows ultrasound to contribute to the diagnosis of internal anomalies that may coincide with external birthmarks.