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Can infection be differential
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Searching PubMed
"Positron Emission Tomography Computed Tomography"[MeSH Terms] AND "head and neck neoplasms"[MeSH Terms] AND "tuberculosis"
Searching PubMed
"Fluorodeoxyglucose F18" AND "false positive" AND "head and neck"
Yes. Infection can be a differential here, but only for some of the findings. The report itself calls everything "suggestive of malignancy", so it doesn't rule infection out.
Patient and report: 47-year-old man with buccal mucosa carcinoma, treated with surgery and radiotherapy. The scan was 18F-FDG PET-CT on 13/11/2026.
Findings by site
| Finding | Malignancy | Infection or inflammation |
|---|---|---|
| Operative bed soft tissue lesion, SUVmax 16.49, extending to the tonsillolingual sulcus and pharyngeal wall | Residual or recurrent tumour is most likely, given the high SUV and the mass-like extension | Post-radiotherapy and post-surgical inflammation, osteoradionecrosis or infected tissue can all take up FDG. These usually give lower, more diffuse uptake. |
| Presternal chest wall deposit, SUVmax 24.82, about 70x47x42 mm, at the right costochondral junction, with cortical irregularity of the manubrium | Metastasis is the leading possibility. | Strongest infection differential. Tubercular cold abscess or osteomyelitis, pyogenic abscess, or fungal or actinomycotic infection can look like this. A sternal or chest wall tubercular abscess is a classic mimic of a metastasis. |
| Left upper lobe cavitary density, SUVmax 3.04 | A cavitating squamous metastasis or a second primary is possible. | Strong infection differential. Pulmonary TB, fungal infection or a lung abscess can cause this. Low SUV with cavitation favours infection, but this does not settle it. |
| Left level II-III and supraclavicular nodes, SUVmax 3.65 and 2.66 | Nodal metastasis is possible. | Reactive nodes or tubercular lymphadenitis. The nodes are small and only mildly avid, so these findings are weak. |
Why infection fits
- The textbooks list FDG false positives from infection and inflammation. These include mycobacterial and fungal infection, granulomatous disease, abscess and chronic lymphadenitis. - Murray & Nadel's Textbook of Respiratory Medicine, section "Interpretation of PET Images"
- Grainger & Allison's Diagnostic Radiology also notes that false-positive results can come from inflammatory or infective causes.
- Fishman's Pulmonary Diseases says benign skeletal conditions, including infection, can give false-positive FDG PET results.
- A cavitary lung nodule suggests necrotising malignancy, particularly squamous cell carcinoma. However, septic emboli, mycobacterial and fungal granulomatous infections and bacterial abscesses are also typical causes. - Fishman's Pulmonary Diseases and Disorders, section "B"
- Case literature describes pulmonary TB mimicking lung cancer on PET/CT (PMID 23474190) and PET/CT findings in pulmonary and spinal TB (PMID 24835666).
- India has a high TB burden. Radiotherapy and cancer both lower immunity.
Points that favour malignancy
- The SUVmax of 24.82 is very high. TB can also reach high SUVs, so this alone does not decide it.
- This is a known squamous cell carcinoma of the buccal mucosa with a bulky local lesion.
- A solid mass with cortical erosion in a patient with known cancer is most likely a metastasis.
How to settle it
- Tissue diagnosis: a biopsy of the sternal lesion, by image-guided FNAC or core biopsy. Send it for histopathology, AFB smear, GeneXpert/CBNAAT, TB culture and fungal stains. This is the most useful step, because treatment changes completely between the two diagnoses.
- Lung lesion: sputum for AFB and CBNAAT, and bronchoscopy with lavage if needed. A CT-guided biopsy is an option.
- Clinical context: fever, night sweats, weight loss, cough, hemoptysis, local pain or swelling, and any TB contact. Also check ESR, CRP, Mantoux or IGRA, and the CBC.
- Operative bed lesion: biopsy or direct endoscopic evaluation, which the oncology team can arrange.
- Dedicated imaging: a dedicated contrast CT or MRI of the chest wall, looking for rim enhancement, a cold abscess with fluid and calcification, and sinus tracts.
- Follow-up PET-CT: the report advises this if the diagnosis stays unclear.
Caution: Don't label this as metastatic disease or as infection from the scan alone. Staging and treatment depend on biopsy results, and your oncologist should make the decision. I could not read the clinical history, so this is a reading of the report only.
Do you want me to go through how to tell tubercular from malignant sternal lesions on imaging?
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