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Light Transillumination

Exams and Signs

Historical Overview

  • Transillumination of an infected digit was first reported by Samuel in 1950 as a technique to determine the precise position of pus by virtue of its darker shade in the otherwise transilluminated pulp.1

Description

  • Other than mineralized bone, most tissues are somewhat translucent: if a bright light is placed in contact with the skin, the unaided eye can observe the spread of light through the immediately adjacent tissue. Transillumination, combined with palpation, offers a simple test of the extent and character of anomalous tissue.

Pathophysiology

  • Pathological changes to soft tissue can change its degree of translucence: a mucous cyst will transmit more light than will normal tissue and appear as a bright area when transilluminated. Pus, or a solid tumor, will tend to be more opaque and appear as a dark area when transilluminated.1,2 However, some solid tumors, such as schwannomas and lipomas are more translucent and can resemble cysts.2

Instructions

  1. Take patient history
  2. Place a light source against the region of interest. Ensure that the light source is shielded such that all of the light escaping it is transmitted into the skin
  3. Compare the transillumination of the suspected pathology with surrounding tissue

Variations

  • Changing the ambient lighting conditions can assist with the observation of transillumination.

Related Signs and Tests

  • Palpation
  • Aspiration

Diagnostic Performance Characteristics

  • Brighter transillumination suggests a ganglion cyst filled with clear liquid. Darker transillumination suggests: a solid tumor or a blood-filled cyst or, in the absence of a palpable hard mass, pus.1,2
  • >One study tested the accuracy of 8 observers using transillumination to distinguish simulated cysts and solid tumors in a cadaver model. The accuracy was 88% (56/64 observations).2
Presentation Photos and Related Diagrams
  • Transillumination of wrist ganglion
    Transillumination of wrist ganglion
  • Excised ganglion and stalk which attached it to wrist joint. Note almost transparent mass.
    Excised ganglion and stalk which attached it to wrist joint. Note almost transparent mass.
  • Excised ganglion. Note almost transparent mass.
    Excised ganglion. Note almost transparent mass.
  • Ganglion does not transilluminate well if the skin thick and/or lesion does not protrude from skin plane.
    Ganglion does not transilluminate well if the skin thick and/or lesion does not protrude from skin plane.
Definition of Positive Result
  • A positive result occurs when there is more or less transillumination at region of interest. 
Definition of Negative Result
  • A positive result occurs when there is more or less transillumination at region of interest. 
Comments and Pearls
  • A small “pen” flashlight is generally suitable for transillumination. If the casing does not overhang the lens, a wrap of opaque tape may be required to prevent light leakage.
  • Lipomas can transilluminate but tend to show more of a "ring flah' affect when this is performed.
  • Transillumination can help prevent mistaking common ganglion cysts from uncommon sarcomas and the necessity of reoperation.3
Diagnoses Associated with Exams and Signs
References
  1. Samuel EP. Transillumination of whitlows of the terminal phalanx. Lancet 1950;1(6608):763-5. PMID: 15416023
  2. Erne HC, Gardner TR, Strauch RJ. Transillumination of hand tumors: a cadaver study to evaluate accuracy and intraobserver reliability. Hand (NY) 2011;6(4):390-3. PMID: 23204965
  3. Crosby SN, Alamanda VK, Weikert DR, Holt GE. Avoiding unplanned resections of wrist sarcomas: an algorithm for evaluating dorsal wrist masses. Am J Orthop 2013;42(9):401-6. PMID: 24078963
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