Cellulitis

What it means

Cellulitis is an infection that spreads through the skin and the layer of soft tissue underneath it, rather than staying in one contained pocket. Bacteria — most often a type of strep or staph — get in through a break in the skin, such as a cut, an insect bite, a surgical incision, or even just very dry or cracked skin, and then spread outward through the tissue. The area becomes inflamed, swollen, and tender, and on imaging that inflammation shows up as a hazy thickening and increased fluid in the fat and soft tissue rather than a defined lump.

Why it appears on a CT or MRI report

Radiologists mention cellulitis when they see stranding — a streaky, hazy pattern — and thickening in the fat just under the skin, usually with mild skin thickening over the top. It is frequently noted near a surgical site, a wound, or an area of recent trauma, because scans done for other reasons (checking for a deeper collection, a fracture, or how well a wound is healing) will pick up this soft-tissue change along the way. Reports often specifically comment on whether there is an underlying abscess (a walled-off pocket of pus) or gas in the tissue, because that changes the treatment plan, and will often state clearly when no abscess is seen.

What it usually means

Cellulitis is one of the most common skin infections and is usually straightforward to treat with a course of oral or, if more severe, intravenous antibiotics. Near a surgical incision, mild redness and soft-tissue swelling in the first week or two can be a normal part of healing rather than true infection, so the finding is interpreted alongside how the wound actually looks and whether there is fever or spreading redness. The main thing radiologists and clinicians want to rule out alongside cellulitis is a deeper abscess or, rarely, a more aggressive infection tracking along muscle or fascia, which need a different, more urgent approach. When a report says an abscess was "ruled out" or "not identified," that is reassuring — it means the infection is likely superficial and should settle with antibiotics alone.

When to follow up

Cellulitis identified on a scan should be discussed with your doctor promptly, generally within a day, so antibiotics can be started or adjusted if they have not been already. Seek urgent care the same day if you notice rapidly spreading redness, a red streak moving up a limb, fever or chills, increasing pain out of proportion to how the area looks, blistering, or a feeling of being generally unwell — these can signal a more serious or deeper infection that needs prompt treatment. Most straightforward cellulitis improves within a few days of starting antibiotics, and follow-up is mainly about making sure the redness and swelling are shrinking rather than growing.

A plain-language way to picture it

Think of the skin and the tissue just under it like a sponge. A pocket of infection (an abscess) is like a marble dropped into the sponge — a defined lump you could point to and would need to squeeze out. Cellulitis is more like spilling a cup of tea onto that same sponge — the liquid spreads outward through the material, soaking a wide, blurry area rather than sitting in one spot. Antibiotics work like letting the sponge dry out from the inside, calming the spread down over a few days.