Lung Carcinoma Radiology

Imaging is central to detecting, characterising, and staging bronchogenic carcinoma. This note covers the chest radiograph and CT signatures of central versus peripheral tumours, Pancoast tumour, hilar/mediastinal disease, obstructive collapse, pleural involvement, histology-specific patterns (including ground-glass adenocarcinoma), and the principles of TNM staging by imaging — the angles NEET PG keeps returning to.

Classification and the radiology-relevant histology

Lung cancers are broadly split into small cell lung carcinoma (SCLC, ~15%) and non-small cell lung carcinoma (NSCLC, ~85%). The NSCLC group includes adenocarcinoma, squamous cell carcinoma (SCC), and large cell carcinoma. The single most useful radiological dichotomy is central versus peripheral location, because it predicts histology, complications, and the imaging appearance.

Feature	Central tumours	Peripheral tumours
Typical histology	Squamous cell carcinoma, SCLC	Adenocarcinoma, large cell
Arises from	Main/lobar/segmental bronchi	Smaller airways / alveoli, lung periphery
Classic X-ray sign	Hilar mass, obstructive collapse/pneumonitis	Solitary peripheral nodule/mass
Cavitation	SCC may cavitate	Less common
Pancoast (apical)	—	Adenocarcinoma/SCC at apex
Relation to smoking	Strong (SCC, SCLC)	Weakest for adenocarcinoma

High-yield: Central = squamous cell carcinoma and small cell carcinoma; peripheral = adenocarcinoma. Adenocarcinoma is now the commonest lung cancer overall and the commonest in non-smokers and women. SCC is the classic cavitating lung cancer.

Chest radiograph features

The plain film is still the first investigation and the source of most exam stems. Recognisable patterns:

• Solitary pulmonary nodule (SPN) — a single round opacity ≤3 cm surrounded by aerated lung. >3 cm is a mass and is malignant until proven otherwise.
• Hilar enlargement / mass — central tumour or nodal disease; look for lobulated, dense, unilateral hilum.
• Obstructive collapse (atelectasis) and obstructive pneumonitis — bronchial occlusion causing volume loss of the distal lung.
• Cavitation — thick (>15 mm), irregular, eccentric wall favours malignancy (classically SCC).
• Apical (Pancoast) opacity with rib/vertebral destruction.
• Pleural effusion, often large and recurrent.
• Elevated hemidiaphragm from phrenic nerve palsy.

Named radiographic signs

High-yield: Golden S sign (reverse S of Golden / S sign of Golden) — right upper lobe collapse around a central obstructing hilar mass produces a concave peripheral collapse and convex central bulge, forming a reverse "S" of the minor fissure. It strongly suggests a central tumour causing RUL collapse.

• Luftsichel sign — a crescent of hyperlucent air (aerated superior segment of lower lobe) seen medially in left upper lobe collapse; "Luftsichel" = air sickle/crescent.
• Rigler notch sign / corona radiata / spiculation — irregular, spiculated margins of a peripheral mass favour malignancy over a benign nodule.
• Cervicothoracic sign — an apical mass whose margin is lost above the clavicles lies posterior (in the mediastinum/posterior thorax), as the anterior mediastinum ends at the clavicles.

Central tumours, hilar enlargement and obstructive collapse

Central bronchogenic carcinoma arises in or near a major bronchus. Endobronchial growth narrows the lumen → impaired ventilation distally. The sequence:

Bronchial obstruction → air resorption → lobar/segmental collapse → +/- obstructive pneumonitis → +/- distal mucoid impaction.

Key signs:

• Hilar enlargement — the commonest manifestation of a central tumour; may be the tumour itself or hilar nodal metastasis.
• Obstructive collapse with displaced fissures, crowded vessels/bronchi, mediastinal shift toward the collapse, and a raised hemidiaphragm.
• Obstructive pneumonitis — consolidation distal to obstruction that does not resolve with antibiotics (a recurrent or non-resolving "pneumonia" in a smoker = suspect cancer).
• On CT, bronchial cut-off with a soft-tissue mass and post-obstructive collapse/mucus.

High-yield: A non-resolving or recurrent pneumonia in the same lobe of an older smoker must prompt a search for an obstructing central bronchogenic carcinoma — do a CT and bronchoscopy.

Peripheral tumours and the solitary pulmonary nodule

A peripheral carcinoma usually presents as an SPN or mass. Distinguishing benign from malignant is a heavily tested topic.

Feature	Favours benign	Favours malignant
Size	<8 mm (low risk)	>3 cm (mass) high risk
Margin	Smooth, well-defined	Spiculated, lobulated, corona radiata
Calcification	Central, laminated/concentric, "popcorn", diffuse	Eccentric, stippled, or absent
Growth (doubling time)	<1 month or >2 years (often stable)	1 month–2 years
Fat within	Present (hamartoma)	Absent
Cavity wall	Thin (<4 mm)	Thick (>15 mm), irregular
Contrast enhancement	<15 HU	>15 HU

High-yield: Four benign patterns of calcification in a nodule are central, diffuse (complete), laminated/concentric, and popcorn (hamartoma). Eccentric or stippled calcification can occur in malignancy. Fat within a nodule = hamartoma (benign). A nodule stable for ≥2 years is very likely benign.

Doubling time refers to volume; a 26% increase in diameter equals a doubling of volume. Malignant nodules typically double in 1 month to 2 years; very fast (<1 month, infection) or very slow (>2 years, benign) growth argues against typical cancer.

Adenocarcinoma and ground-glass opacity

Adenocarcinoma has a characteristic CT spectrum reflecting its lepidic (along alveolar walls) growth, which is a favourite high-yield topic since the reclassification that abolished "bronchioloalveolar carcinoma (BAC)."

• Pure ground-glass nodule (GGN) — hazy increased attenuation that does NOT obscure underlying vessels/bronchi. Correlates with adenocarcinoma in situ (AIS) or atypical adenomatous hyperplasia; indolent.
• Part-solid (mixed) nodule — a GGO with a solid component; the solid portion correlates with invasion and carries the highest malignancy risk among nodule types.
• Solid nodule — invasive adenocarcinoma or other histology.

High-yield: A persistent part-solid nodule has the highest probability of malignancy. The size of the solid component drives both invasiveness and the T descriptor in current TNM (T is measured on the solid/invasive component, not the whole GGO). Multifocal GGOs suggest multifocal adenocarcinoma (formerly multicentric BAC).

Other adenocarcinoma signs: pleural tag/tail (linear strand to the pleura), bubble-like lucencies (pseudocavitation), and the CT halo sign (ground-glass rim) — though halo is classically described in angioinvasive aspergillosis.

Pancoast (superior sulcus) tumour

A tumour at the lung apex/superior sulcus invading the thoracic inlet. Usually NSCLC (adeno or SCC).

Apical mass → invades brachial plexus (C8–T1), sympathetic chain, and ribs/vertebrae.

Clinico-radiological features:

• Pancoast syndrome — shoulder/arm pain along C8–T1, wasting of small hand muscles.
• Horner syndrome — ptosis, miosis, anhidrosis, enophthalmos (sympathetic chain/stellate ganglion involvement).
• Radiograph: apical soft-tissue cap with rib/vertebral destruction; asymmetric apical thickening >5 mm warrants CT/MRI.

High-yield: MRI is the imaging modality of choice for Pancoast tumour to assess brachial plexus, subclavian vessels, vertebral, and chest-wall invasion — these determine resectability.

Pleural and chest-wall involvement

• Malignant pleural effusion — exudative, often haemorrhagic, recurrent; categorised as M1a (within thoracic cavity).
• Pleural nodularity, circumferential/mediastinal pleural thickening, and "rind" suggest malignant pleural disease (differential: mesothelioma, metastases).
• Chest-wall invasion (rib destruction, soft-tissue mass, obtuse angle with pleura, >3 cm contact) = T3.

Diagnosis and investigation of choice

A stepwise imaging-to-tissue approach:

1. Chest radiograph (PA + lateral) — first test; detects mass, collapse, effusion.
2. Contrast-enhanced CT chest + upper abdomen (to adrenals/liver) — investigation of choice for characterising and staging the primary and nodes.
3. PET-CT (FDG) — best for distant metastases and mediastinal nodal staging (high sensitivity); upgrades/downstages and guides nodal sampling. Brain (low FDG uptake) needs separate imaging.
4. MRI brain — for cerebral metastases (especially SCLC, adenocarcinoma) and for Pancoast local extent.
5. Tissue diagnosis — bronchoscopy + biopsy/EBUS for central lesions; CT-guided percutaneous biopsy for peripheral lesions; pleural fluid cytology/biopsy for effusions.

High-yield: CECT chest is the investigation of choice for evaluating and staging a lung mass; PET-CT is best for detecting distant metastases and nodal staging; MRI is best for Pancoast tumour and brain metastases. Tissue diagnosis is mandatory before treatment.

TNM staging principles (imaging)

Staging uses the TNM system; recent NEET PG questions track the size-based T cut-offs.

Descriptor	Imaging definition (key cut-offs)
T1	≤3 cm surrounded by lung/visceral pleura (T1a ≤1, T1b >1–2, T1c >2–3 cm)
T2	>3–5 cm, OR involves main bronchus/visceral pleura, OR atelectasis/obstructive pneumonitis
T3	>5–7 cm, OR chest wall/phrenic nerve/parietal pericardium, OR separate nodule same lobe
T4	>7 cm, OR invades mediastinum, heart, great vessels, trachea, carina, oesophagus, vertebra, diaphragm; OR separate nodule different ipsilateral lobe
N1	Ipsilateral hilar/peribronchial nodes
N2	Ipsilateral mediastinal/subcarinal nodes
N3	Contralateral mediastinal/hilar or any scalene/supraclavicular nodes
M1a	Malignant pleural/pericardial effusion or contralateral lung nodule
M1b/M1c	Single / multiple distant metastases

High-yield: A short-axis mediastinal node >1 cm on CT is considered enlarged (suspicious), but CT size alone is unreliable — PET-CT and tissue sampling (EBUS/mediastinoscopy) confirm nodal stage. N3 or M disease generally means unresectable.

High-yield: SCLC is staged separately and pragmatically as limited stage (confined to one hemithorax/single radiation port) versus extensive stage. SCLC presents as a central mass with bulky mediastinal/hilar adenopathy and is usually unresectable — treated primarily by chemotherapy +/- radiotherapy.

Management/treatment of choice (radiology-relevant)

• NSCLC, early stage (I–II, resectable): surgery (lobectomy) is the treatment of choice; SBRT/stereotactic radiotherapy if inoperable.
• NSCLC locally advanced (III): concurrent chemoradiotherapy +/- immunotherapy.
• NSCLC metastatic (IV): systemic therapy guided by molecular markers (EGFR, ALK, PD-L1).
• SCLC: chemotherapy (platinum-etoposide) is the mainstay +/- thoracic and prophylactic cranial radiotherapy.
• Pancoast tumour: neoadjuvant chemoradiotherapy followed by surgery if resectable.

Complications

• Post-obstructive pneumonia/abscess and recurrent infections.
• Lobar collapse with respiratory compromise.
• Superior vena cava (SVC) obstruction — usually a right-sided central tumour or SCLC; facial/arm swelling, distended neck veins; CT shows SVC narrowing with collaterals.
• Pancoast/Horner syndrome.
• Phrenic nerve palsy (raised hemidiaphragm) and recurrent laryngeal nerve palsy (hoarseness, left more common).
• Malignant pleural and pericardial effusion, tamponade.
• Lymphangitis carcinomatosa — interlobular septal thickening, nodular thickening, often unilateral in lung cancer.
• Metastases — brain, bone (lytic), liver, adrenal.

Key differentials of a lung mass/nodule

Differential	Distinguishing imaging clue
Hamartoma	"Popcorn" calcification, intralesional fat
Tuberculoma / granuloma	Central/laminated calcification, satellite nodules, stable
Carcinoid	Central, strongly enhancing, well-defined endobronchial nodule
Pulmonary metastases	Multiple, well-defined "cannonball" nodules, basal/peripheral
Round pneumonia / abscess	Air bronchograms, thin smooth cavity wall, clinical sepsis
Aspergilloma	Mass within cavity, air-crescent sign, mobile
Lymphoma / mesothelioma	Bulky nodes / circumferential pleural rind

Recently asked / exam angle

• Golden S sign identification on a chest X-ray → RUL collapse with central hilar mass (central carcinoma).
• Most common lung cancer overall and in non-smokers = adenocarcinoma; central cavitating = SCC; central with bulky nodes = SCLC.
• Investigation of choice distinctions: CECT for primary/staging, PET-CT for metastases/nodes, MRI for Pancoast and brain.
• Benign vs malignant nodule — patterns of calcification, fat = hamartoma, doubling time, thick irregular cavity wall.
• Part-solid GGN = highest malignancy risk; T measured on solid component.
• Pancoast tumour → Horner syndrome, MRI for resectability.
• Luftsichel sign = left upper lobe collapse.
• SVC obstruction most often from right-sided/SCLC central tumour.
• Malignant pleural effusion = M1a and confers unresectability.

Rapid revision

1. Central tumours = SCC and SCLC; peripheral = adenocarcinoma (commonest overall, commonest in non-smokers).
2. SCC is the classic cavitating cancer (thick, irregular, eccentric wall >15 mm).
3. Golden S sign = RUL collapse around a central obstructing mass; Luftsichel = LUL collapse.
4. Non-resolving/recurrent pneumonia in a smoker → exclude obstructing central carcinoma.
5. Benign nodule calcification: central, diffuse, laminated, popcorn; fat = hamartoma.
6. Nodule stable ≥2 years is likely benign; malignant doubling time 1 month–2 years.
7. Part-solid GGN has the highest malignancy risk; T = solid component size.
8. CECT is investigation of choice for the primary/staging; PET-CT best for metastases/nodes.
9. MRI is best for Pancoast tumour (brachial plexus/vessels) and brain metastases.
10. Pancoast → C8–T1 pain + Horner syndrome (ptosis, miosis, anhidrosis).
11. Mediastinal node >1 cm short-axis = suspicious, but confirm with PET-CT/EBUS.
12. Malignant pleural effusion = M1a (unresectable); SCLC = limited vs extensive stage, chemo-based.