13.3 Thoracic and Abdominal Imaging Conditions

13.3 Thoracic and Abdominal Imaging Conditions

Quick Answer: Lumbar and thoracic spine radiographs routinely capture the mediastinum, lung apices, abdominal aorta, kidneys, and bowel gas pattern at their margins. Part II tests whether you can recognize these incidental visceral findings — widened mediastinum, apical lung mass, AAA calcification, bowel obstruction, free air — and apply the correct triage decision before any chiropractic intervention proceeds.

Why Visceral Findings Appear on Chiropractic Films

Doctors of chiropractic order plain-film radiographs of the spine for musculoskeletal complaints, but the field of view routinely includes thoracic and abdominal soft-tissue structures. A patient presenting with thoracic pain may have an apical lung tumor; a patient with low back pain may have an abdominal aortic aneurysm or bowel obstruction visible on the lumbar series. Part II Diagnostic Imaging items in this subtopic test pattern recognition plus triage urgency — not definitive diagnosis of chest or abdominal disease, but whether the finding changes the treatment plan and how quickly referral is needed.

Thoracic Soft-Tissue Findings

Mediastinal Silhouette

The mediastinum is bounded by the sternum, vertebral column, and pleural cavities. On a well-positioned PA chest film, the mediastinal contour is smooth and symmetric with recognizable borders: aortic knob (left), right atrial border (right), and a cardiothoracic ratio ≤0.5.

Mediastinal widening — transverse measurement exceeding roughly 8 cm on an upright PA film, or a mediastinum-to-chest-width ratio above 0.25 — is a high-yield finding. Causes include:

• Traumatic aortic injury after deceleration trauma — an emergency; do not adjust, refer immediately
• Lymphadenopathy from lymphoma, metastatic disease, or granulomatous disease (sarcoidosis, tuberculosis)
• Anterior mediastinal masses — thymoma, germ cell tumors, thyroid goiter ("4 T's": thymus, teratoma, thyroid, terrible lymphoma)
• Aortic aneurysm — focal bulge along the aortic contour
• Technical rotation — falsely widens the mediastinum; confirm symmetric clavicle-to-spinous-process positioning before calling a pathologic finding

Lung Apex Lesions

The lung apices are visible on lateral cervical and upper thoracic spine films. Key patterns:

• Pancoast tumor (superior sulcus tumor): Apical opacity with first-rib or transverse-process erosion, ipsilateral Horner syndrome (ptosis, miosis, anhidrosis) from stellate ganglion involvement, and shoulder pain radiating down the ulnar nerve distribution
• Apical tuberculosis: Fibrocavitary disease with upper-lobe predilection, often with calcified granulomata and hilar lymphadenopathy
• Pleural thickening or apical cap: Bilateral, symmetric apical thickening is often a benign post-inflammatory scar; unilateral, progressive thickening warrants further evaluation

Pleural and Cardiac Findings

• Pleural effusion: Blunting of the costophrenic angle (minimum ~200 mL to detect on upright film), meniscus sign, mediastinal shift away from a large effusion
• Pneumothorax: Visceral pleural line with absent peripheral lung markings; tension pneumothorax adds mediastinal shift toward the contralateral side and is an emergency
• Cardiomegaly: Cardiothoracic ratio >0.5 on PA film suggests enlargement; different chamber enlargements produce characteristic contour changes (left atrial enlargement = "double density" and splayed carina; left ventricular enlargement = elongated left heart border)

Benign Thoracic Calcifications

Not every calcification requires referral. Normal age-related variants include:

• Costochondral cartilage calcification — irregular, bilateral, at costochondral junctions
• Granulomatous calcified lymph nodes — from prior histoplasmosis or tuberculosis exposure
• Aortic and mitral annular calcification — common in older adults

Abdominal Soft-Tissue Findings

Abdominal Aortic Aneurysm (AAA)

Atherosclerotic aortic wall calcification produces a curvilinear density paralleling the lumbar vertebral bodies at L1–L4.

• Normal aortic width: generally <3 cm wall-to-wall between calcified margins
• Aneurysmal dilation: ≥3 cm; rupture risk rises sharply above 5–5.5 cm (surgical threshold)
• "Double lucent line" sign on lateral lumbar film — two parallel calcified lines representing near and far walls of a dilated aorta
• Rupture triad: hypotension, severe abdominal/back pain, pulsatile abdominal mass — emergency

The Part II scenario: a lumbar series for low back pain incidentally reveals aortic calcification exceeding 3 cm. Correct response is referral for vascular imaging (ultrasound or CT) and avoidance of high-velocity thrust over the aortic region until evaluated.

Organomegaly and Silhouette Signs

Solid organs displace adjacent bowel gas and alter normal soft-tissue outlines:

• Hepatomegaly: Right upper quadrant mass effect, inferior displacement of the right kidney and hepatic flexure
• Splenomegaly: Left upper quadrant fullness, inferior displacement of the splenic flexure and left kidney
• Psoas shadow asymmetry: Loss of one psoas margin suggests retroperitoneal pathology (abscess, hematoma, tumor) — the psoas margin is normally visible as a soft-tissue stripe lateral to the lumbar spine

Phleboliths Versus Ureteral Calculi

This is a classic Part II distractor pairing on pelvic/lumbar films:

Bowel Gas Patterns

• Normal: Scattered gas in small and large bowel; haustral markings in colon
• Ileus: Diffuse, dilated loops of small and large bowel without a transition point — often postoperative or metabolic
• Small bowel obstruction: Dilated small-bowel loops (>3 cm) with air-fluid levels on upright film, string-of-beads sign (valvulae conniventes crossing the full bowel width), and a transition point where dilated proximal bowel meets collapsed distal bowel
• Large bowel obstruction: Dilated colon (>6 cm) with haustral markings that do not cross the full width (unlike valvulae conniventes); cecal diameter >9 cm risks perforation

Free Air (Pneumoperitoneum)

Free air beneath the diaphragm on an upright chest or abdominal film indicates hollow-viscus perforation — a surgical emergency. Causes include perforated peptic ulcer, diverticulitis, colonic perforation, and postoperative leak. Even a small amount of free subdiaphragmatic air is significant. This finding overrides any musculoskeletal complaint and requires immediate emergency referral.

Triage Framework for Part II

Exam Strategy

Visceral imaging items on Part II almost always pair a spine-film finding with a clinical scenario. Ask three questions: (1) Is this finding pathologic or a benign variant? (2) Does it contraindicate chiropractic treatment? (3) How urgently must the patient be referred? When in doubt between phlebolith and ureteral stone, look for the central lucency and comet-tail sign (phlebolith) versus alignment along the ureteral path (stone). When aortic calcification exceeds 3 cm, always choose referral over reassurance.