Using Transillumination to Diagnose a Foreign Body

Transilluminated foot.

A 4-year-old female, who is otherwise healthy, presented to the emergency department (ED) for evaluation of left foot pain. Three days prior, the patient had been on a wooden dock with family friends. She suddenly developed pain to the plantar aspect of the foot without any obvious trauma. She had not ambulated since then. At urgent care, two small splinters were removed from the foot and a small amount of purulence was noted. She was discharged home with expectant management. After continuing to have poor pain control, the mother brought her to the ED. She was vitally stable and afebrile, but unable to be consoled. On physical exam, she cried continuously and had significant tenderness to the plantar aspect at the distal second and third metatarsals. Purulence was able to be expressed from a small opening as well.

FIGURE 1: Radiograph of foot without identifiable foreign body. (Click to enlarge.)

The X-ray of the foot was read as “Salter-Harris III fracture involving the proximal 1st metatarsal. There was no evidence of foreign body” (Figure 1). In discussion with orthopedics, this was thought to be a variant and not the cause of her pain. With further discussion with the mother, she mentioned they had transilluminated the foot at home and thought they saw “something.” Indeed, with transillumination of the foot in the exam room with a light from a cell phone showed a faint linear foreign body was appreciated at approximately four cm in length (Figure 2). Podiatry was consulted and they recommended an MRI and antibiotics, plan for operative removal given the purulence and her level of discomfort. MRI did not appreciate a foreign body due to what was initially thought to be motion artifact (Figure 3). She was still brought to the operating room and an eight cm wooden splinter was removed from her foot. She was discharged from the hospital the following day on levaquin and cephalexin. Her wound culture ultimately grew Clostridium tertium.

FIGURE 2: X-ray of foot revealing faint linear foreign body. (Click to enlarge.)

Foreign body-related injuries are often missed on first visits and are common causes of malpractice claims. There were more than eight million ED visits for open wounds.3 One study evaluating foreign bodies in cadaver feet evaluated sensitivity and specificity for detection via radiographs, CT, and MRI. Overall detection for radiography was 29 percent (sensitivity) and 100 percent (specificity), 63 percent and 98 percent for CT, and 58 percent and 100 percent for MRI.4 Interestingly, CT was superior to MRI in identifying water-rich fresh wood. Ultrasound has become a highly reliable modality for detecting non-radiopaque foreign bodies. Sensitivity and specificity were 63 percent and 95 percent respectively in a study from 2013.4 Although, this is often operator dependent and can be difficult given echo patterns which vary with size, nature, and retention time.2 In areas such as hands and feet, transillumination can also help identify the presence of a retained foreign body, as in this case.

FIGURE 3: MRI of foot without identifiable foreign
body secondary to motion artifact. (Click to enlarge.)

  • Transillumination can be used in soft tissue areas to further evaluate foreign bodies. Many foreign bodies are not radiopaque for X-ray imaging, and this was nearly missed on MRI due to the small nature.
  • Early closure is a pitfall that was thankfully avoided by listening to the parents.
  • Ultrasound could also be an imaging modality, if the patient would tolerate this.

Dr. Anderson is a board-certified emergency physician at a community hospital in St. Cloud, MN.

Mr. Miller is a first-year medical student at the University of Minnesota-Duluth.

  1. Campbell EA, Wilbert CD. (2023). Foreign body imaging. In: StatPearls (Internet). Treasure Island (FL): StatPearls Publishing; 2024. Accessed February 27, 2024.
  2. Chen K-C, Lin AC-M., Chong CF, et al (). An overview of point-of-care ultrasound for soft tissue musculoskeletal applications in the emergency department. J Intens Care. 2016;4:55.
  3. Halaas GW. (). Management of foreign bodies in the skin. Am Fam Physician.2007;76(5):683-8.
  4. Pattamapaspong N, Srisuwan T, Sivasomboon C, et al. Accuracy of radiography, computed tomography and magnetic resonance imaging in diagnosing foreign bodies in the foot. La Radiologia Medica. 2013;118, 303-10.
  5. Wright E, Somwaru B. POCUS and soft tissue foreign bodies. REBELEM website. Published January, 2021. Accessed February 27, 2024.