Foreign body granuloma is a chronic inflammatory granulomatous reaction developing against a foreign body remaining in soft tissue (glass, wood, metal, thorn, splinter, plastic, surgical material). US is the primary diagnostic modality and the foreign body itself appears as a hyperechoic linear structure; posterior acoustic shadowing (glass, metal, bone) or posterior reverberation artifact (metal, glass) are pathognomonic findings. Surrounding granulation tissue appears as hypoechoic halo or mass. US sensitivity for foreign body detection is 87-98% and is superior to radiography because it can also demonstrate non-opaque materials (wood, plastic, thorn).
Age Range
5-80
Peak Age
30
Gender
Equal
Prevalence
Common
Foreign body granuloma is a type IV delayed hypersensitivity reaction developing against foreign material that enters tissue and cannot be removed. Macrophages attempt to phagocytose the foreign body but cannot digest large or inert materials — consequently, epithelioid cells and multinucleated giant cells (Langhans type) form and granulomatous inflammation develops. Granulation tissue contains new capillaries, fibroblasts, and collagen — on US, this tissue appears as hypoechoic halo because the vascular and cellular structure shows different acoustic impedance from surrounding fat and connective tissue. The hyperechoic appearance of the foreign body on US results from the large acoustic impedance difference between foreign material and surrounding tissue — glass (~13 × 10⁶ kg/m²s), metal (~45 × 10⁶ kg/m²s), wood (~2-4 × 10⁶ kg/m²s) all have higher impedance compared to soft tissue (~1.6 × 10⁶ kg/m²s), creating strong reflection. Posterior acoustic shadowing results from the foreign body blocking ultrasound wave transmission — high-attenuation materials (glass, metal) do not transmit energy to the distal region, creating shadow. Reverberation artifact in highly reflective flat-surfaced materials (metal, glass) results from multiple back-and-forth reflections of the ultrasound wave between the material-tissue interface and probe surface — each reflection cycle produces an echo, creating a series of equally spaced parallel echoes.
The combination of hyperechoic linear structure with posterior acoustic shadowing and/or reverberation artifact in soft tissue is the pathognomonic US finding for foreign body, seen in all foreign body types including non-opaque materials.
On B-mode US, the foreign body appears as a hyperechoic linear or fragmented linear structure. Glass and metal foreign bodies show prominent posterior acoustic shadowing. Wood and organic materials may have more irregular contours and their echogenicity may change over time due to swelling. Size, depth, and orientation of the foreign body can be accurately assessed with US.
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A hyperechoic linear structure with posterior acoustic shadowing is seen in the soft tissue, consistent with a foreign body.
Posterior reverberation (comet-tail) artifact may be seen with metallic and glass foreign bodies — appearing as a series of equally spaced parallel echogenic lines distal to the foreign body. This artifact results from multiple reflections of the ultrasound wave between the highly reflective flat surface of the foreign body and probe surface, having pathognomonic diagnostic value.
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Reverberation (comet-tail) artifact is noted distal to the foreign body, suggesting metallic/glass material.
A hypoechoic halo (granulation tissue) develops around chronic foreign bodies. This halo represents the granulomatous inflammatory reaction surrounding the foreign body. Halo thickness is directly proportional to chronicity and inflammation severity. In some cases, granulation tissue may form an irregular hypoechoic mass mimicking a tumor.
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A hypoechoic halo representing granulation tissue is seen surrounding the foreign body, consistent with chronic foreign body reaction.
On power Doppler, minimal-mild peripheral vascularity may be detected in granulation tissue surrounding the foreign body. This vascularity reflects chronic inflammatory neovascularization. The foreign body itself is avascular. Absence of internal vascularity is a distinguishing finding from solid tumors.
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Minimal peripheral vascularity is noted in granulation tissue surrounding the foreign body on power Doppler.
On CT, metal and glass foreign bodies show high density. Glass is generally >100 HU, metal >1000 HU. Wood and organic materials show low density and detection is more difficult — near air density in acute phase, may approach soft tissue density in chronic phase after water absorption.
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A high-density structure is seen within the soft tissue on CT, consistent with a foreign body (glass/metal).
On MRI, the foreign body generally shows low signal on all sequences (signal void) — especially metal foreign bodies create prominent susceptibility artifact. Surrounding granulation tissue shows low-intermediate signal on T1, high signal on T2, and enhancement. MRI may be contraindicated for metallic foreign bodies (ferromagnetic risk).
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Enhancing granulomatous tissue surrounding a low-signal structure is seen on MRI, consistent with foreign body granuloma.
Criteria
High impedance, prominent shadowing and/or reverberation, visible on radiography
Distinct Features
Easily detected by US and radiography. High density on CT.
Criteria
Low-intermediate impedance, shadowing present in acute phase may diminish in chronic phase, not visible on radiography
Distinct Features
US is primary diagnostic modality (radiography negative). Echogenicity may change in chronic phase from water absorption. Higher infection risk.
Criteria
Surgical history, foreign body location consistent with surgical field
Distinct Features
Suture granuloma most commonly encountered type in postoperative period. Hyperechoic focus + peripheral granulation tissue on US.
Distinguishing Feature
Hematoma does not contain hyperechoic linear structure, shows time-dependent echogenicity change, avascular. Granuloma contains central hyperechoic foreign body.
Distinguishing Feature
Glomus tumor is subungual, hypervascular, contains no foreign body structure. Granuloma shows foreign body + shadowing/reverberation.
Distinguishing Feature
Fibromatosis is fascia-associated fusiform nodule, no foreign body structure. Granuloma shows central foreign body + peripheral granulation pattern.
Urgency
routineManagement
surgicalBiopsy
Not NeededFollow-up
3-monthSymptomatic foreign bodies should be surgically removed. US-guided localization increases surgical success rate — preoperative US determines depth, orientation, and relationship to adjacent structures. Asymptomatic, deep-seated inert foreign bodies may be followed. If infection develops, antibiotherapy + drainage is required.
Treatment of foreign body granuloma is surgical removal of the foreign body. US-guided localization improves surgical success. Antibiotic treatment is added for infected granulomas. Wooden foreign bodies carry high infection risk. Some foreign bodies (silicone, suture reaction) may cause chronic granulomatous reaction.