Infection on PET-CT
Fungal Infection and Abscess — on PET-CT
Both fungal infections and abscesses show up on PET-CT scans, and they can appear as bright as cancer. A hot spot on a scan is not the same as finding cancer — but it does mean your team needs to work out what the cause is.
Medically reviewed by Dr. C. Raghavendra Reddy, Medical Oncologist, MBBS (Gold Medal) · DNB · DM (Medical Oncology, Gold Medal) · Last reviewed September 2026
- Infections do show up — Fungal infections and abscesses are metabolically active and accumulate glucose on PET-CT, just as tumours do.
- Intensity is not a diagnosis — A very bright finding can be infection, inflammation, or cancer. The uptake value alone does not tell them apart.
- Pattern helps, tissue decides — The shape of uptake offers clues, but biopsy or culture is usually needed to confirm what a finding is.
- Immunosuppressed patients are most at risk — Patients on chemotherapy, steroids, or with blood cancers have the highest risk of invasive fungal infections.
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Yes, both fungal infections and abscesses accumulate glucose on PET-CT, often as intensely as cancer. There is no uptake threshold that reliably separates infection from malignancy. Your team uses your clinical history, blood tests for fungal markers, and usually a tissue sample to establish what the finding represents.
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Do fungal infections and abscesses show up on PET-CT?
Yes — both show up, and for the same reason cancer does. PET-CT measures glucose uptake, and the inflammatory cells that flood an infected area are highly metabolically active. They consume glucose intensely.
This means PET-CT picks up active infections reliably. It also means a hot spot on the scan cannot be assumed to be cancer simply because it is bright.
In India, this differential is especially important. Tuberculosis, fungal infections, and cancer can all appear as bright lesions in the lungs, lymph nodes, or elsewhere on PET-CT. The scan begins the investigation. It does not end it.
How bright does an infection appear — could it look like cancer?
Fungal infections and abscesses can appear as intensely bright on PET-CT as many cancers. The uptake intensity overlaps substantially between infection and malignancy. There is no threshold value your radiologist can use to say with certainty which one a finding is.
The shape of uptake sometimes offers clues. An abscess often shows a ring of bright uptake around a cooler centre. Certain fungal lesions in the lung have characteristic appearances on the CT component of the scan. Radiologists note these patterns, but they support a hypothesis — they do not confirm a diagnosis.
Your radiologist will describe what the scan shows and list the most likely explanations. Your clinical team then decides which fits best given everything else they know about you.
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How does your team tell infection apart from cancer on the scan?
The scan is one piece of evidence. Your team combines it with your clinical history — whether you have fever, whether you are immunosuppressed, whether you have been recently unwell — and with blood tests.
For fungal infections specifically, blood tests for markers such as galactomannan can point toward Aspergillus. These are not cancer markers, but they help narrow the differential.
When the picture remains unclear, tissue is needed. A biopsy or fluid sample can be sent for histopathology — to look for cancer cells — and microbiological culture — to identify any organism present. Both questions can often be answered from the same sample.
Tell your team about any new symptoms between appointments. Fever, new pain, or breathlessness should be reported the same day, not saved for your next scheduled visit.
Questions people in this situation ask most
Am I at higher risk for fungal infection because I am on chemotherapy?
Yes. Chemotherapy suppresses the immune system, which reduces your ability to contain fungi that a healthy immune system would normally keep in check. Invasive fungal infections — including Aspergillus and Candida — are significantly more common in patients on cancer treatment. If you develop fever, a new cough, or chest pain during or between cycles, report it the same day rather than waiting for your next appointment.
If a hot spot turns out to be infection, does that mean cancer is not there?
No. A finding attributed to infection does not clear the rest of the scan. Cancer and infection can coexist in the same patient, and sometimes in the same site — a partially broken-down tumour can harbour organisms. Your team interprets each finding in the context of the full clinical picture. One explanation does not close the question for everything else.
What is galactomannan and why has my doctor ordered it?
Galactomannan is a component of the cell wall of Aspergillus, a fungus that causes serious lung infections in immunosuppressed patients. When Aspergillus is active, galactomannan can be detected in blood or in fluid from the lungs. A positive result, in the right clinical context, supports a diagnosis of invasive Aspergillus infection. It is not a cancer test. Your doctor may order it when fungal infection is part of the differential.
Does the pattern of uptake on PET-CT help identify the cause without a biopsy?
Pattern raises or lowers probability — it does not replace tissue diagnosis when the stakes are high. A ring of uptake around a cold centre suggests an abscess. Certain fungal infections have recognisable appearances in the lung. These features inform the clinical hypothesis. When a cancer diagnosis is being made or reconsidered, pattern alone is rarely sufficient — tissue confirmation protects you from both under-treatment and over-treatment.
Will a follow-up PET-CT look normal once the infection is treated?
Treating an active infection usually reduces the uptake it was causing, but how much and how quickly depends on the type of infection and your response to treatment. Your team will typically arrange a follow-up scan after treatment. A finding that resolves or significantly improves after antibiotics or antifungals supports infection as the cause. If any uptake persists or changes shape, further assessment may still be needed.
What if the biopsy finds both infection and abnormal cells?
This is uncommon but it can happen. Some cancers create local conditions that favour infection — a necrotic tumour can harbour organisms. Finding infection in a biopsy does not mean the tissue is free of cancer cells. Your pathologist reports both findings separately, and your oncologist uses the full report to decide next steps. Both issues can often be addressed in parallel, and both need to be considered.
PET-CT at CION starts from Rs 10,499 — among the lowest published prices in Hyderabad — across 4 partner centres in Banjara Hills, Punjagutta, Himayatnagar and Narayanaguda. Indicative price, as of September 2026.
Explore 94 more Understanding Your PET-CT Report topics
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- Dental Infection and Jaw Uptake on PET
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- An Incidental Bone Finding on PET-CT
- An Incidental Breast Finding on PET-CT
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- Incidental Findings on a PET-CT Scan: What They Are
- Incidental Heart Findings on a Cancer PET Scan
- The Cost of Chasing an Incidental Finding
- What to Ask Your Doctor About an Incidental Finding
Reading Your Report: Core Terms
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- 'Deauville Score' on a Lymphoma PET Report
- 'FDG Avid': What It Means on Your Report
- 'Hypermetabolic': What the Word Actually Means
- 'Hypometabolic' and 'Photopenic' Findings
- 'Impression' vs 'Findings': Which Section Should You Read?
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- 'Metabolically Active Disease': What It Tells You
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- 'No Abnormal FDG Uptake': Is That a Clear Scan?
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- 'Sub-Centimetre Node' and Why Size Matters on PET
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- How Long Does a PET-CT Report Take?
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- Should You Read Your Own PET-CT Report Before the Consult?
- TNM Staging on a PET-CT Report
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Response Assessment Scores & Criteria
- Complete Metabolic Response: What It Means
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- End-of-Treatment PET Scan: What It Decides
- How Doctors Judge Whether Treatment Is Working on PET-CT
- Interim PET Scan During Chemotherapy: Why It Is Done
- Metabolic Response vs Size Response: Why They Differ
- PERCIST Criteria: How Metabolic Response Is Measured
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SUV Values Explained
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- Does a Higher SUV Mean a More Aggressive Cancer?
- Factors That Change Your SUV Reading
- High SUV but Not Cancer: When the Number Misleads
- Is My SUVmax of 4 High? Reading Your Specific Number
- Low SUV but Still Cancer: The PET-Negative Cancers
- SUV in Non-Cancer Conditions
- SUVmax, SUVmean and SUVpeak: What Is the Difference?
- What Is SUV on a PET Scan?
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- What SUV Value Indicates Cancer?
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Common questions
Frequently asked questions
Do all infections light up on PET-CT, or only serious ones?
Most active infections produce some FDG uptake because they involve metabolically active inflammatory cells. Superficial infections may show only faint uptake. Invasive infections — including abscesses and invasive fungal disease — commonly produce intense uptake that can resemble cancer. There is no reliable threshold that separates trivial from serious, or infection from malignancy. Your radiologist and oncologist assess uptake within the full clinical picture rather than from the number alone.
Which fungal infections are most common in cancer patients in India?
Aspergillus is the most common invasive fungal infection in patients with blood cancers or on high-dose chemotherapy. Candida is more common in those with prolonged antibiotic use or central lines. Mucormycosis occurs more often where diabetes coexists with immunosuppression. Your team will consider which organisms are most likely based on your specific treatment, blood counts, and clinical situation — not from the imaging alone.
What cancers are most often confused with fungal infection on PET-CT?
Lung lesions cause the most diagnostic difficulty. Invasive Aspergillus in the lung can look very similar to primary lung cancer or pulmonary metastases on both the PET and CT components. Enlarged lymph nodes caused by infection rather than tumour involvement are also a source of confusion. Tuberculosis, bacterial pneumonia, and sarcoidosis add to the same differential in India. The approach to resolving all of these is clinical assessment combined with tissue diagnosis.
How is tissue taken from a deep hot spot in the lung or abdomen?
For lung lesions, bronchoscopy — a camera through the airway — can collect washings or a small biopsy. CT-guided needle biopsy reaches deeper chest lesions through the chest wall. Abdominal collections are often sampled by ultrasound or CT-guided drainage. The approach depends on where the finding is and your overall condition at the time. Your team will explain the options and the procedure before anything is done.
Does treating the infection affect how accurately PET-CT tracks my cancer?
Yes. Active infection creates false-positive findings — areas that look like cancer spread but are caused by inflammation rather than tumour cells. This makes accurate staging harder. Your radiologist will flag possible non-malignant uptake, but the picture is clearer once infection is resolved. This is one reason your team may want to clarify an ambiguous finding before changing your cancer treatment plan.
Can cancer treatment and treatment for the infection happen at the same time?
In many cases, yes. Antifungal or antibiotic treatment can run alongside cancer treatment, or during a brief pause, depending on your condition and whether the medicines interact. Your oncologist and the relevant specialist coordinate this. Starting treatment for infection does not mean cancer treatment has permanently stopped — your team will tell you when it is safe to continue or resume.