Foreign Bodies in the Skin: Ultrasound as a High-Precision Detector

Dr. Segnini
Dec 19, 2025
3 min read

Updated: Dec 22, 2025

Dr. Segnini Foreign body in skin ultrasound

When Exploration Is Not Enough

Wood splinters, glass fragments, thorns, needles, graphite shavings, or metal splinters are foreign bodies that can penetrate the skin after an accident, a fall, or everyday activity. Often, the superficial wound closes, but the fragment remains inside, potentially causing persistent pain, infection (abscess), granulomatous inflammation, or damage to nearby structures such as tendons or nerves. When the object is not visible or palpable, ultrasound becomes the imaging method of choice for its detection and localization.

Why is ultrasound the best tool for this problem?

Ultrasound far surpasses X-rays in this field, with decisive advantages:

High Resolution for Surface Structures: It is exceptionally good for visualizing the dermis, subcutaneous cellular tissue, and fascia.
Radiopacity Independent : X-rays only see radiopaque objects (metals, some types of glass). Ultrasound detects any material that has a different density than the surrounding soft tissue, including wood, thorns, plastic, and fiberglass , which are radiolucent.
Real-Time and Dynamic Visualization: Allows you to see the relationship of the foreign body with the anatomical structures in motion (tendons, muscles).
Millimeter Precision for Extraction: Provides a 3D "treasure map" (depth, distance to vessels/nerves), drastically reducing surgery time, incision size and damage to healthy tissue.
Active Extraction Guide: Can be used in the same surgical procedure to guide the forceps or scalpel directly towards the object.

Ultrasound Findings: The Signature of Different Materials

The sonographic appearance of a foreign body depends on its composition, size, shape, and the tissue reaction it elicits. The key is to look for a disruption of the normal architecture of the soft tissues.

1. Direct Ultrasound Signs:

Hyperechoic (Bright) Structure : Most foreign bodies appear as very bright ( hyperechoic ) spots or lines due to the large difference in density with the surrounding soft tissue. This is typical in:
- Glass: Very hyperechoic , with a sharp posterior acoustic shadow (a black area behind).
- Metal: Intense hyperechoic , with a posterior acoustic shadow of "comet tail" or reverberation (repetitive parallel lines behind the object).
- Plastic/Hard: Less echoic than metal/glass, but still visible.
Hypoechoic (Dark) Structure : Organic objects such as wood or thorns often appear in the initial stages as hypoechoic (dark) lines or fragments , and may be surrounded by a hyperechoic halo due to the foreign body reaction. Over time, they become more hyperechoic .

2. Indirect Ultrasound Signs (Tissue Reaction):

These signs are sometimes the only clue and are crucial for locating small or poorly echogenic fragments :

Hypoechoic Halo (Edema or Granuloma): A dark area surrounding the foreign body, caused by inflammation and fluid accumulation.
Abscess Formation: A fluid collection ( anechoic or with debris ) that can form around the infected object.
"Invisible" Foreign Body: If the inflammatory reaction is intense, the object may be completely enveloped in a hypoechoic granuloma , this lump being the key to its location.

Exploration Protocol: A Systematic Search

Medical History and Physical Examination: Knowing the suspicious material and the point of entry is fundamental.
Exploration Technique:
- high-frequency linear transducer (12-18 MHz) is used for maximum surface resolution.
- Apply plenty of gel to avoid excessive compression and to displace surface objects.
- It is explored methodically and slowly , in two orthogonal planes (longitudinal and transverse), starting from the point of pain.
Pre-Surgical Marking: Once located, its projection in both planes is marked on the skin. Its depth from the skin is measured , and its relationship to critical structures (vessels, tendons, nerves) is described.
Intraoperative Ultrasound : In complex cases, the probe (with sterile sheath) can be used in the operating room to confirm location and guide extraction in real time.

Limitations and Challenges

Minimum Size: Objects smaller than 1-2 mm may go unnoticed.
Deep Localization: Its resolution decreases in very deep objects.
Very Soft Material: Objects such as textile fibers are extremely difficult to visualize.
Operator Experience: Interpretation requires practice to distinguish a foreign body from other normal structures (fascia, vessels) or scars.

Conclusion: Precision that Avoids Complications Foreign body in skin ultrasound

When a foreign body is suspected, ultrasound is the surgeon's natural extension of their eyes . It transforms a blind search, which often results in large and repeated incisions, into a minimally invasive, rapid, and highly effective procedure . Its ability to detect non-radiopaque materials and guide their removal with millimeter precision makes it an indispensable tool in Emergency Medicine, Traumatology, and Plastic Surgery, ensuring better recovery and fewer complications for the patient.