27. Principles of Interpretation of PET-CT Data in Suspected Tumor Infiltration

• SUV (Standardized Uptake Value): SUV >2.5 is highly suspicious for malignancy. It reflects the degree of FDG uptake relative to body weight and injected dose.
• Visual correlation: A "hot spot" on PET must be anatomically correlated with CT findings (mass, consolidation, lymph node enlargement).
• Staging value: PET-CT is superior to CT alone or PET alone for identifying mediastinal lymph node involvement and extrathoracic metastases (especially in NSCLC).
• Nodule size threshold: PET is most reliable for lesions >15 mm; lesions <8 mm frequently yield false negatives.
• False negatives: Seen in:
  • Hyperglycemia / diabetes (competitive glucose inhibition)
  • Slow-growing tumors (carcinoid, well-differentiated adenocarcinoma)
  • Small lesions (<8 mm)
• False positives: Active infections (TB, fungal), sarcoidosis, inflammatory granulomas — all can show elevated FDG uptake.
• Interpretation rule: Never interpret PET alone — always integrate with CT morphology, clinical context, and if needed, histological confirmation.

28. Role of Bronchoscopy in Differential Diagnosis of Infiltrative Syndrome

• Infectious: Bacterial pneumonia, TB, invasive pulmonary aspergillosis (BAL galactomannan + culture), PCP
• Malignant: Primary lung cancer, lymphoma, carcinomatous lymphangitis (cytology/biopsy)
• Non-infectious inflammatory: Sarcoidosis, hypersensitivity pneumonitis, cryptogenic organizing pneumonia (BAL lymphocytosis + TBB)
• Alveolar hemorrhage: BAL showing progressively bloodier return

• Low yield for peripheral nodular lesions — percutaneous CT-guided biopsy preferred
• BAL contraindicated in severe hypoxemia, refractory thrombocytopenia, or coagulopathy

29. Diagnostic Role of Microbiological Methods (Sputum Culture, PCR) in Infiltrative Changes

• Indication: First-line in community-acquired and hospital-acquired pneumonia presenting as consolidation/infiltrate
• Validity criteria: Adequate specimen = >25 neutrophils and <10 squamous epithelial cells per low-power field
• Identifies: Streptococcus pneumoniae, Klebsiella, Pseudomonas, Staphylococcus, Mycobacteria (AFB smear + culture)
• Limitations: Low sensitivity (~50%) due to prior antibiotics, specimen quality, fastidious organisms; results take 24–72h (mycobacteria up to 6 weeks)
• BAL culture is superior to expectorated sputum for immunocompromised patients and atypical organisms

• High sensitivity and specificity, rapid turnaround (hours)
• Key applications in infiltrative syndrome:
  • Respiratory multiplex PCR panels: Detect influenza, RSV, SARS-CoV-2, adenovirus, atypical bacteria simultaneously
  • Mycobacterium tuberculosis PCR (Xpert MTB/RIF): Detects TB and rifampicin resistance in sputum/BAL within 2 hours
  • Pneumocystis jirovecii PCR: High sensitivity in BAL — preferred over staining in immunocompromised
  • Fungal PCR (Aspergillus): Supplementary to galactomannan in BAL
  • Legionella PCR: When urinary antigen is negative but clinical suspicion remains high

30. Principles of Pathogenetic Therapy for Diseases Accompanied by Infiltrative Syndrome

Infectious Infiltration (e.g., pneumonia)

• Antimicrobials eliminate the causative agent → reducing inflammatory mediator release
• Mucolytics (ambroxol, acetylcysteine) → improve mucociliary clearance

Autoimmune / Inflammatory Infiltration (e.g., sarcoidosis, COP, hypersensitivity pneumonitis)

• Corticosteroids (prednisone): Suppress macrophage and lymphocyte activation, reduce granuloma formation
• Immunosuppressants (azathioprine, methotrexate, mycophenolate): Used in steroid-dependent or steroid-refractory cases (e.g., ILD, vasculitis)
• Biologic agents (rituximab, infliximab): In specific autoimmune-mediated infiltration (ANCA vasculitis, refractory sarcoidosis)

Tumor Infiltration

• Chemotherapy / targeted therapy (TKIs, immunotherapy): Reduce tumor mass and lymphangitic spread
• Anti-edema therapy (dexamethasone): Reduces peritumoral inflammation

Allergic Infiltration (eosinophilic pneumonia, ABPA)

• Corticosteroids are first-line
• Antifungals (itraconazole) in ABPA — reduce antigenic stimulus

Fibrotic Infiltration (IPF)

• Antifibrotics (nintedanib, pirfenidone): Slow progression by inhibiting fibroblast proliferation and TGF-β signaling

31. Use of Antibacterial Drugs in Treatment of Infiltrative Syndrome

1. De-escalation: Start broad empirically, narrow when cultures/sensitivity results available
2. Duration: CAP typically 5–7 days; confirmed S. aureus/Pseudomonas or complicated cases may require 14–21 days
3. Route: Oral in mild CAP; IV in hospitalized patients, switch to oral when clinically stable
4. Monitoring: Clinical response expected within 48–72h; failure to improve → broaden coverage, consider resistant organisms, non-bacterial etiology, or complications (empyema, abscess)
5. Combination therapy rationale: Covers atypical organisms not covered by beta-lactams alone (Legionella, Mycoplasma, Chlamydophila)
6. Avoid antibiotics when infiltrate is non-bacterial (viral pneumonia without bacterial superinfection, eosinophilic pneumonia, organizing pneumonia) — this is a common exam point.

27. PET-CT Interpretation in Suspected Tumor Infiltration

• SUV > 2.5 = highly suspicious for malignancy (tumor cells consume more glucose → "hot spot")
• Always correlate PET finding with CT anatomy — never interpret alone
• Best for lesions >15 mm; unreliable for <8 mm
• Superior to CT alone for mediastinal lymph nodes and distant metastases

• Diabetes, small lesions, slow-growing tumors (carcinoid)

• TB, fungal infection, sarcoidosis — all show high FDG uptake

When in doubt → biopsy for confirmation

28. Role of Bronchoscopy in Differential Diagnosis of Infiltrative Syndrome

• Pneumonia (bacterial, fungal, TB)
• Lung cancer / lymphoma
• Sarcoidosis, organizing pneumonia
• Alveolar hemorrhage (BAL turns progressively bloody)

• Poor yield for peripheral lesions → use CT-guided biopsy instead
• Avoid if: severe hypoxemia, severe thrombocytopenia

29. Microbiological Methods (Sputum Culture & PCR) in Infiltrative Changes

Sputum Culture

• Identifies bacterial pathogens causing infiltration
• Valid specimen: >25 neutrophils, <10 epithelial cells per field
• Takes 24–72h (TB culture: up to 6 weeks)
• Limitation: low sensitivity (~50%), affected by prior antibiotics

PCR

• Faster, more sensitive than culture
• Key uses:

30. Principles of Pathogenetic Therapy in Infiltrative Syndrome

31. Antibacterial Drugs in Treatment of Infiltrative Syndrome

Empirical Therapy by Setting:

Key Rules:

1. Start broad → narrow once culture results return (de-escalation)
2. Expect improvement in 48–72h — if no response, broaden or reconsider diagnosis
3. Duration: CAP = 5–7 days; complicated = up to 14–21 days
4. IV → switch to oral once patient is stable
5. Do NOT give antibiotics for viral pneumonia, eosinophilic pneumonia, or organizing pneumonia — common exam trap