Seroma is a sterile serous fluid collection that develops after surgery or trauma. Serous fluid seeping from transected lymphatic and blood vessels accumulates in the dead space. It is most commonly seen after mastectomy, abdominoplasty, hernia repair, liposuction, and lymph node dissection. Incidence varies from 15-80% depending on surgery type. Clinically, it presents as a painless, fluctuant swelling at the surgical site. Most seromas resolve spontaneously; persistent or symptomatic ones may require aspiration. If infection develops, it can transform into an abscess. Ultrasonography is the primary diagnostic modality — diagnosed by anechoic fluid collection, thin wall, avascular content, and surgical/trauma history.
Age Range
20-80
Peak Age
50
Gender
Equal
Prevalence
Common
Seroma formation is a process triggered by tissue damage during surgery or trauma. Lymphatic vessels and blood capillaries are transected → lymphatic fluid and serum (protein-rich plasma filtrate) accumulate in dead space. The inflammatory response also contributes: tissue damage → proinflammatory cytokines → increased capillary permeability → exudative fluid. Serous fluid is a clear-yellow transudate/exudate mixture with low cell content. It appears anechoic on ultrasonography because the fluid is acoustically homogeneous — no particles to scatter (unlike purulent abscess or hematoma). The thin wall (pseudocapsule) forms from fibroblast proliferation. Prominent posterior enhancement because serous fluid attenuation is very low (≈0.02 dB/cm/MHz). Avascular because the collection contains no vascular component. Spontaneous resolution occurs through lymphatic drainage and capillary absorption.
An anechoic, thin-walled, avascular fluid collection at the surgical site in a patient with surgical/trauma history strongly supports seroma diagnosis. Clinical-radiological correlation is essential for differentiation from abscess (heterogeneous, rim vascularity, cellulitis) and hematoma (echogenic, time-dependent signal changes).
On B-mode ultrasonography, an anechoic or low-echogenic, well-defined fluid collection is seen at the surgical/trauma site. The wall is thin (<1 mm), smooth-bordered with pseudocapsule structure. Internal structure is typically homogeneously anechoic — no particles or debris. Prominent posterior acoustic enhancement. Seroma size can vary from a few millimeters to 15-20 cm. Shape may be oval, lenticular, or irregular — conforming to surgical bed anatomy.
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A thin-walled, anechoic, well-defined fluid collection with prominent posterior enhancement is seen at the surgical site; consistent with postoperative seroma.
No vascular signal is detected within the seroma or its wall on Color and Power Doppler — completely avascular. This finding is the most critical ultrasonographic criterion for differentiating seroma from abscess (which shows rim vascularity). No inflammatory hyperemia in surrounding tissues (unless infected). Minimal reactive vascularity in surrounding tissues may be seen in chronic seromas.
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No vascular signal detected within the fluid collection or its wall on Color Doppler; avascular structure consistent with non-infected seroma.
No cobblestone pattern (perilesional cellulitis) in subcutaneous fat around the seroma — fat lobules show normal echogenicity and normal separation. This negative finding is as important as positive findings in differentiating seroma from abscess. No surrounding tissue edema or hyperemia in non-infected seroma. However, in the early postoperative period (<1-2 weeks), mild perilesional edema may be seen due to surgical trauma — these are normal postoperative changes.
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No cellulitis findings (cobblestone pattern) in subcutaneous fat surrounding the fluid collection; no findings suggesting infection.
The seroma collection may be partially compressed with probe pressure — confirming fluid collection. No pulsation — important for differentiation from vascular pseudoaneurysm. Fluid movement may be observed during compression-decompression but no debris movement (squish sign) as in abscess — anechoic fluid contains no particles.
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The fluid collection is partially compressible with probe pressure and shows no pulsation.
On CT, a low-density (0-20 HU), well-defined fluid collection is seen at the surgical/trauma site. No enhancement on contrast-enhanced sequences — thin wall may show minimal enhancement. No inflammatory stranding in surrounding fat (unless infected). Density value near water, varying 5-15 HU depending on protein content.
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A low-density, non-enhancing fluid collection is seen at the surgical site; consistent with postoperative seroma.
On T2-weighted MRI, seroma shows homogeneous high signal — reflecting long T2 relaxation time of serous fluid. Low signal on T1. No enhancement on contrast-enhanced sequences. No diffusion restriction on DWI — free fluid does not restrict water molecule movement (different from abscess).
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The lesion shows homogeneous hyperintense signal on T2-weighted images with no diffusion restriction on DWI; consistent with seroma.
Criteria
Develops within first 2-4 weeks after surgery/trauma. Anechoic, smooth-walled collection.
Distinct Features
Completely anechoic, thin wall, minimal surrounding tissue reaction. Most resolve spontaneously. Aspiration rarely needed.
Criteria
Seroma persisting longer than 4-6 weeks. Wall thickening and fibrous organization.
Distinct Features
Thickened wall (pseudocapsule), septations may develop, low-level internal echoes (protein accumulation), mild wall vascularity. Aspiration or sclerotherapy may be needed.
Criteria
Infection developing from secondary bacterial contamination. Fever, pain, erythema develop clinically.
Distinct Features
Heterogeneous internal structure (debris), rim vascularity develops, perilesional cellulitis/cobblestone pattern appears — transformation to abscess. Emergency drainage + antibiotics needed.
Distinguishing Feature
Abscess shows heterogeneous fluid (debris), rim vascularity, and perilesional cellulitis (cobblestone). Seroma is anechoic, avascular, no cellulitis. Clinically abscess presents with fever and pain.
Distinguishing Feature
Ganglion shows joint/tendon stalk — no surgical history. Typical periarticular location. Seroma is at surgical site without stalk.
Distinguishing Feature
Lipoma is solid, isoechoic/hyperechoic with parallel echogenic lines — not a fluid collection. Compressible with no posterior enhancement.
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
3-monthSeroma is a benign process and most (80-90%) resolve spontaneously within 4-8 weeks. Follow-up is sufficient for asymptomatic small seromas. US-guided aspiration may be performed for symptomatic ones — but repeat aspiration may be needed (50-70% recurrence). Sclerotherapy or surgical capsulectomy for chronic persistent seromas. If infection signs develop, emergency drainage and antibiotics are needed. Prevention includes dead space minimization, closed drainage systems, and compression.
Small seromas usually resolve spontaneously. Aspiration is performed for large or symptomatic seromas. Compression bandage is applied for recurrent seromas. Infected seroma may progress to abscess formation — if rim vascularity develops, antibiotic therapy and drainage are needed. Chronic seromas may encapsulate and require surgical excision.