Image Interpretation III: Tumors, Miscellaneous Osteoarticular Disease and Soft Tissue

A lytic hole in a vertebra can be a harmless hemangioma, a myeloma, or a metastasis that will collapse next week; a dense vertebra can be Paget disease or prostate cancer. The board shows you the film and asks what it is, what else it could be, and how fast the patient must be seen. This chapter teaches a systematic approach to bone lesions, the hallmarks of tumors, infection, vascular and metabolic disease, and the chest and abdominal findings that turn up on spinal films, each with the recommendation you would write.

Section 1Benign tumors and tumor like lesions

A systematic approach to any bone lesion

Before naming a lesion, describe it. The features that predict behavior are, in order of usefulness:

• Age of the patient: the single most powerful filter. Under 30, think of primary tumors and cysts; over 40, think first of metastasis and myeloma, whatever the lesion looks like.
• Number: multiple lytic lesions in an older adult are metastasis or myeloma until proven otherwise.
• Location: in a long bone, epiphysis (chondroblastoma, giant cell tumor after physeal closure, infection), metaphysis (most primary tumors: osteosarcoma, osteochondroma, simple bone cyst, nonossifying fibroma) or diaphysis (Ewing sarcoma, fibrous dysplasia, myeloma, lymphoma); central, eccentric or cortical. In the spine, the body (hemangioma, metastasis, myeloma, giant cell tumor, chordoma) versus the posterior elements (osteoid osteoma, osteoblastoma, aneurysmal bone cyst).
• Margin and zone of transition (Lodwick pattern): a geographic lesion with a thin sclerotic rim and a narrow zone of transition grows slowly and is usually benign. A geographic lesion without a rim is less certain (giant cell tumor, myeloma). A moth eaten pattern (multiple coalescing holes) or a permeative pattern (innumerable tiny holes with a wide, indistinct zone of transition) indicates aggressive disease: Ewing sarcoma, lymphoma, myeloma, metastasis or osteomyelitis.
• Matrix: chondroid matrix forms rings and arcs or popcorn calcification (enchondroma, chondrosarcoma); osteoid matrix is fluffy, cloudlike and dense (osteosarcoma); ground glass is fibrous dysplasia.
• Periosteal reaction: solid or thick undulating reaction means slow, benign processes; lamellated (onion skin), spiculated (sunburst or hair on end) and the Codman triangle (periosteum lifted at the edge of a mass) mean an aggressive lesion that outruns the periosteum.
• Soft tissue mass and cortical destruction favor malignancy or infection.

Benign lesions of the spine

Vertebral hemangioma is the most common benign tumor of the spine, present in roughly 10 percent of adults, usually in the thoracic or lumbar body. Thick vertical trabeculae separated by lucent vascular spaces produce the corduroy (or jailhouse, vertical striation) appearance on plain film and the polka dot appearance on axial CT. The body is normal in size and shape; the lesion is bright on both T1 and T2 MRI because of fat. Nearly all are incidental. Rarely, an aggressive hemangioma expands into the posterior elements and canal and causes cord compression, especially in pregnancy. Recommend nothing further for a typical lesion; recommend MRI only if there are neurological signs or atypical features.

Osteoid osteoma occurs from about age 10 to 25, more in males, in the femur and tibia (cortical diaphysis or metaphysis) and in the posterior elements of the spine. The hallmark is a small lucent nidus under 1.5 cm, sometimes with a central dot of calcification, surrounded by dense reactive sclerosis that may hide the nidus on plain film (CT shows it best). The history is diagnostic: night pain relieved dramatically by aspirin or NSAIDs (the nidus produces prostaglandins). In the spine it causes painful scoliosis with the lesion on the concave side near the apex. Differential: Brodie abscess (lucent tract), stress fracture (linear), osteoblastoma (nidus over 1.5 to 2 cm, less sclerosis, less NSAID response). Refer for CT guided radiofrequency ablation. Osteoblastoma is the larger cousin: expansile, posterior elements of the spine in about 40 percent, and it may behave aggressively.

A bone island (enostosis) is a dense focus of compact bone in the medulla, round or oval, with brush border thorny spicules blending into surrounding trabeculae. It is common in the pelvis and proximal femur, is usually under 1 cm and is "cold" or only mildly warm on bone scan. A dense lesion that is large, growing or hot on bone scan in an older adult needs workup for blastic metastasis.

Cartilage lesions

Osteochondroma (exostosis) is the most common benign bone tumor. It is a cartilage capped bony projection from the metaphysis, most often around the knee and proximal humerus, that points away from the joint. The defining feature is that the cortex and medulla of the lesion are continuous with those of the parent bone. It may be pedunculated (on a stalk) or sessile. Growth stops at skeletal maturity. Malignant transformation to chondrosarcoma occurs in under 1 percent of solitary lesions and in a few percent of hereditary multiple exostoses. Warning signs are new pain or growth after skeletal maturity, a cartilage cap thicker than about 1.5 to 2 cm on MRI, and irregular calcification in the cap. Osteochondromas also cause mechanical symptoms: bursitis, tendon snapping, nerve or vessel compression and fracture of the stalk.

Enchondroma is a medullary cartilage tumor, the most common tumor of the small bones of the hand (phalanges and metacarpals), where it is a well defined lytic lesion with endosteal scalloping, mild expansion and stippled or rings and arcs calcification. It often presents with a pathological fracture. In long bones, the distinction from low grade chondrosarcoma is critical: enchondromas are painless, small, and scallop less than two thirds of the cortical thickness. Ollier disease is multiple enchondromas; Maffucci syndrome is multiple enchondromas with soft tissue hemangiomas (phleboliths visible on film); both carry a high risk of chondrosarcoma.

Cysts and fibrous lesions

The simple (unicameral) bone cyst occurs before age 20, in the proximal humerus or proximal femur, as a central metaphyseal lytic lesion with a thin sclerotic margin and mild expansion. Its long axis parallels the shaft, and it migrates away from the physis with growth. It usually presents with fracture, and a fragment of cortex may fall to the dependent part of the fluid filled cyst: the fallen fragment sign, which is pathognomonic.

The aneurysmal bone cyst (ABC) also occurs under age 20 but is eccentric, markedly expansile and blown out, with a thin eggshell cortex and internal septations (soap bubble). In the spine it involves the posterior elements and may extend into the body. MRI shows fluid fluid levels. About a third are secondary to another lesion (giant cell tumor, chondroblastoma, osteosarcoma, especially telangiectatic osteosarcoma, which must be excluded).

The nonossifying fibroma (and its small cortical version, the fibrous cortical defect) is an eccentric, metaphyseal, lytic lesion with a scalloped, sclerotic, often multilocular border in a child or teenager, most often around the knee. It is a classic do not touch lesion that heals by sclerosis.

Fibrous dysplasia replaces medullary bone with fibrous tissue and woven bone. Lesions are long, expansile, and have a hazy ground glass matrix with a thick sclerotic margin (the rind sign). Common sites are the ribs (the most common benign rib lesion), proximal femur (where repeated microfractures produce the shepherd crook deformity), tibia, skull and facial bones (leontiasis ossea). It may be monostotic (about 70 to 80 percent) or polyostotic. McCune Albright syndrome combines polyostotic fibrous dysplasia, cafe au lait spots with irregular coast of Maine borders, and precocious puberty or other endocrinopathy.

Giant cell tumor

Giant cell tumor (GCT) occurs between about 20 and 40, after physeal closure. It is a lytic, eccentric, epiphyseal lesion that extends from the metaphysis to within about 1 cm of the subarticular bone, with a narrow zone of transition but no sclerotic margin. Sites are the distal femur, proximal tibia and distal radius; in the spine, the sacrum is classic. It is locally aggressive, recurs after curettage in a meaningful fraction, and rarely metastasizes to lung. The four rules for GCT are: open physes exclude it, it reaches the articular surface, it is eccentric, and its margin is not sclerotic.

Section 2Primary malignant and metastatic disease

Why age and location decide most cases

Primary malignant bone tumors are rare; metastases are far more common than all primary bone malignancies combined in adults, and multiple myeloma is the most common primary malignancy of bone. A destructive lesion in a patient over 40 is metastasis or myeloma until proven otherwise. Primary sarcomas cluster by age: osteosarcoma and Ewing sarcoma in the second decade, chondrosarcoma after 40, and secondary osteosarcoma in older adults with Paget disease or prior radiation.

Osteosarcoma

Conventional osteosarcoma has a peak between about 10 and 25 years with a second peak in older adults (secondary to Paget disease or radiation). About half arise around the knee (distal femur, proximal tibia), then the proximal humerus, in the metaphysis. The film shows a poorly defined, mixed lytic and sclerotic lesion with cloudlike osteoid matrix, cortical destruction, a soft tissue mass containing tumor bone, and aggressive periosteal reaction: sunburst spiculation and Codman triangles. Pain that is constant and worse at night, swelling and a mass are typical; alkaline phosphatase may be raised. Lungs are the main metastatic site, so chest CT is part of staging. Variants: parosteal osteosarcoma (adults 20 to 40, a dense lobulated mass stuck to the posterior distal femur, with a thin lucent cleft between tumor and cortex; low grade) and telangiectatic osteosarcoma (lytic, mimics ABC).

Chondrosarcoma

Chondrosarcoma affects adults over about 40, in the pelvis, proximal femur, shoulder girdle and ribs. It is a lytic lesion with chondroid (rings and arcs) matrix that differs from an enchondroma by being larger (over about 5 cm), painful, by deep endosteal scalloping over two thirds of the cortical thickness, by cortical thickening or breakthrough, periosteal reaction and a soft tissue mass. Pain in a known cartilage lesion of a long bone or pelvis in an adult is a red flag. It may arise from an enchondroma or osteochondroma (secondary chondrosarcoma).

Ewing sarcoma

Ewing sarcoma is a small round blue cell tumor (EWSR1 translocation, typically t(11;22)) of children and teenagers aged about 5 to 20. It arises in the diaphysis or metadiaphysis of long bones and in flat bones (pelvis, ribs, scapula). The classic film shows a permeative lytic lesion with a wide zone of transition, lamellated (onion skin) periosteal reaction, sometimes a saucerized cortex and a large soft tissue mass out of proportion to the bone change. Because patients often have fever, raised ESR and leukocytosis, it mimics osteomyelitis; other differentials are lymphoma and Langerhans cell histiocytosis (eosinophilic granuloma, which in the spine causes vertebra plana, a uniformly flattened body in a child).

Multiple myeloma and plasmacytoma

Multiple myeloma is a malignant plasma cell proliferation in adults over about 50, presenting with bone pain (often back pain), fatigue, recurrent infections and the CRAB features: hypercalcemia, renal insufficiency, anemia and bone lesions. Laboratory clues are a very high ESR, rouleaux on the smear, a monoclonal (M) protein on serum protein electrophoresis and immunofixation, serum free light chains, and Bence Jones protein in the urine. Radiographic patterns:

• Multiple small, round, uniform, punched out lytic lesions without sclerotic rims, especially in the skull (raindrop skull), spine, ribs, pelvis and proximal long bones.
• Diffuse osteopenia with multiple compression fractures, which may be indistinguishable from osteoporosis on film (the most common presentation in the spine).
• Endosteal scalloping of long bones.
• Because myeloma begins in the vertebral body (red marrow) and lacks osteoblastic response, the pedicle is preserved until late, unlike metastasis; and bone scan is often cold (normal), so a skeletal survey, low dose whole body CT, MRI or PET CT is used instead.

A solitary plasmacytoma is a single expansile lytic lesion, often in a vertebral body or pelvis, sometimes with a soap bubble look; many progress to myeloma. POEMS syndrome is a rare sclerotic form.

Skeletal metastasis

Metastases travel in the blood to red marrow, so they favor the axial skeleton: spine (especially the thoracic and lumbar bodies, via the valveless Batson venous plexus), pelvis, ribs, skull and proximal femur and humerus. Lesions below the elbow and knee are uncommon (acral metastases suggest lung primary). The most common primaries are breast, prostate, lung, kidney and thyroid (with breast and prostate dominating), plus myeloma and lymphoma in the differential.

About 30 to 50 percent of trabecular bone must be lost before a lytic lesion is visible on plain film, so a normal film does not exclude metastasis; MRI is the most sensitive test for the spine, and bone scan screens the whole skeleton for blastic and mixed disease. The pedicle sign (winking owl sign) is the classic plain film finding: on the AP lumbar or thoracic view, each vertebra resembles an owl face with the pedicles as eyes, and destruction of one pedicle makes the owl wink. The pedicle is destroyed because the tumor extends from the posterior body into the pedicle; it is often the first visible sign. Other signs are a collapsed body with a convex posterior border, an ill defined lytic area in a body, a soft tissue mass and, typically, a preserved disc space (tumors spare the disc, infection destroys it).

The ivory vertebra (a uniformly dense body of normal size) has a short differential: blastic metastasis (prostate, breast), Hodgkin lymphoma and Paget disease. Paget disease enlarges the body and thickens its cortex (picture frame), whereas metastasis and lymphoma do not enlarge it; anterior scalloping suggests lymphoma. Low grade infection and osteoid forming tumors are rare causes.

Chordoma, from notochord remnants, is the most common primary malignant tumor of the sacrum in adults (the sacrococcygeal region and the clivus are the classic sites): a midline destructive sacral lesion with a large soft tissue mass and amorphous calcification, often presenting with long standing low back or coccyx pain and later bowel or bladder change. Lymphoma of bone produces permeative destruction with a soft tissue mass, often with surprisingly preserved cortex.

Writing the recommendation for a suspicious lesion

For a lesion that looks aggressive, the report should say so in plain words, give the differential in order, and recommend the next steps: MRI with contrast of the region, laboratory work (CBC, ESR or CRP, calcium, alkaline phosphatase, serum protein electrophoresis with free light chains, PSA in men), chest imaging, and prompt referral to the primary physician or oncology. Urgency rises sharply with neurological findings: new weakness, sensory level, or bowel and bladder change in a patient with known or suspected cancer means metastatic spinal cord compression, an emergency that needs same day MRI and corticosteroids. Manipulation of an involved segment is contraindicated; a pathological fracture can follow a modest force.

Section 3Hematologic, vascular and infectious disease

Sickle cell disease and other anemias

In sickle cell disease, sickled cells occlude small vessels, causing bone infarcts, while chronic hemolysis drives marrow hyperplasia. The radiographic signs follow from these two processes:

• H shaped vertebrae (Lincoln log vertebrae): square central depressions of the end plates from infarction of the central end plate supplied by end arteries, with the periphery spared. This is nearly pathognomonic.
• Avascular necrosis of the femoral and humeral heads, often bilateral.
• Bone infarcts in the medullary cavity: serpiginous, sclerotic, calcified borders in the metaphysis and diaphysis.
• Dactylitis (hand foot syndrome) in infants, with periosteal reaction of the small tubular bones.
• Osteomyelitis, where Salmonella is unusually common (though Staphylococcus aureus remains frequent).
• Marrow expansion: osteopenia, widened medullary spaces, and in the skull a widened diploic space with hair on end striations, more marked in thalassemia major, which also causes rodent facies, obliterated sinuses and paraspinal masses from extramedullary hematopoiesis.

Avascular necrosis and the osteochondroses

Avascular necrosis (AVN, osteonecrosis) of the femoral head results from interrupted blood supply. Remember the causes with ASEPTIC: alcohol and AIDS, steroids and SLE, sickle cell, pancreatitis, trauma (femoral neck fracture, hip dislocation), idiopathic (Legg Calve Perthes), infection, caisson disease (dysbaric) and Gaucher disease. Patients present with groin pain and painful internal rotation. Radiographic stages (Ficat and Arlet style): stage I normal film (MRI positive with the double line sign), stage II mottled sclerosis and lucency with a preserved round head, stage III the crescent sign (a subchondral lucent line that marks collapse of the necrotic segment) and flattening, stage IV secondary osteoarthritis with joint space loss. MRI is the most sensitive test and should be ordered for a high risk patient with hip pain and normal films; early referral matters because core decompression works only before collapse.

The osteochondroses are AVN of a growth center in children and adolescents:

Osteomyelitis

Hematogenous osteomyelitis in children lodges in the metaphysis, where slow flow in looping capillaries favors bacterial seeding; Staphylococcus aureus is the most common organism at all ages. Adults more often have spinal infection or contiguous spread (diabetic foot ulcers, open fractures, surgery). The key radiographic fact is the delay: bone destruction is not visible for about 10 to 14 days. The sequence is deep soft tissue swelling with loss of fat planes (days), then ill defined metaphyseal lysis and periosteal reaction (1 to 2 weeks), then in chronic infection a sequestrum (a dense fragment of dead bone), an involucrum (a shell of new periosteal bone around it) and a cloaca (an opening through which pus drains). A Brodie abscess is a subacute, well walled off lucency with a sclerotic rim, often with a serpiginous tract toward the physis. MRI is the best early test; ESR and CRP are raised. Septic arthritis is an emergency, with joint aspiration the key test; in a child, fever, refusal to bear weight, ESR over 40 and WBC over 12,000 (Kocher criteria) predict septic arthritis rather than transient synovitis.

Discitis and vertebral osteomyelitis

In adults, spinal infection usually starts at the vertebral end plate and spreads across the disc to the next vertebra (spondylodiscitis). Risk factors are age over 50, diabetes, intravenous drug use, immune suppression, recent urinary tract infection, endocarditis and spinal procedures. Patients have constant, severe back pain, often fever (absent in up to half), and a very high ESR and CRP. The radiographic sequence:

• First, disc space narrowing (within the first 2 to 3 weeks).
• Then loss of the end plate cortical line and erosion of the adjacent end plates on both sides of the disc.
• Later, destruction of the bodies, paraspinal soft tissue swelling and, with healing, reactive sclerosis and eventual bony fusion.

The defining contrast with tumor is the disc: infection crosses and destroys it, while metastasis and myeloma usually spare it. Degenerative disc disease narrows the disc too, but the end plates stay sharp and sclerotic, with osteophytes and often a vacuum phenomenon (gas virtually excludes infection). Recommend urgent MRI with contrast, ESR, CRP, CBC and blood cultures, and same day medical referral; neurological deficit or sepsis means emergency department. In children, discitis presents as refusal to walk or sit, or back or abdominal pain, and the disc space narrows a few weeks later.

Tuberculous spondylitis (Pott disease)

Spinal tuberculosis favors the thoracolumbar junction and lower thoracic spine. It begins in the anterior vertebral body, spreads beneath the anterior longitudinal ligament to involve multiple contiguous (and sometimes skip) levels, causes anterior wedging and collapse with a sharp angular kyphosis (gibbus), and forms a large paraspinal (cold) abscess that may calcify and track along the psoas into the groin. Compared with pyogenic infection, it is slower (months), the disc is relatively preserved early, sclerosis is less, and constitutional symptoms (weight loss, night sweats) are prominent. Risk groups include immigrants from endemic areas, people with HIV and the incarcerated. Peripheral tuberculous arthritis shows Phemister triad: juxta articular osteoporosis, peripheral (marginal) erosions and gradual joint space narrowing (pyogenic arthritis narrows the joint rapidly). Refer for MRI, chest film, interferon gamma release assay or skin test, and infectious disease care.

Section 4Nutritional, metabolic and endocrine disease

Osteoporosis

Osteoporosis is a reduced quantity of normally mineralized bone. Plain film is insensitive: about 30 to 50 percent of bone mass must be lost before it looks osteopenic, so the diagnosis rests on DXA (T score of minus 2.5 or lower at the spine, hip or forearm; minus 1.0 to minus 2.5 is osteopenia) or on a fragility fracture. The film shows increased radiolucency, thin pencil line cortices, loss of horizontal trabeculae with accentuated vertical trabeculae (which can mimic hemangioma, but the body is uniformly involved), the empty box look, and fractures: wedge fractures in the thoracic spine (producing a dowager hump), biconcave (codfish) vertebrae in the lumbar spine, and fractures of the hip, distal radius and sacrum. Secondary causes to consider are glucocorticoids, hyperthyroidism, hyperparathyroidism, hypogonadism, malabsorption, myeloma, and immobilization. Steroid induced osteoporosis often shows dense marginal condensation of the end plates.

Before you call it osteoporosis in an older adult, exclude myeloma and metastasis (SPEP, calcium, CBC) when there are atypical features. Recommend DXA, a basic metabolic workup, vitamin D, and medical management, and modify manipulative technique (low force, no long lever thrusts) in proportion to bone fragility.

Osteomalacia and rickets

Osteomalacia is inadequate mineralization of osteoid in adults, from vitamin D deficiency (poor sun, malabsorption, liver or kidney disease) or phosphate wasting. Labs show low or normal calcium, low phosphate, high alkaline phosphatase, low 25 hydroxy vitamin D and raised PTH. The film shows osteopenia with blurred, fuzzy trabeculae and the hallmark Looser zones (pseudofractures, Milkman syndrome): bilateral, symmetric, transverse lucent bands with sclerotic margins running perpendicular to the cortex, typically at the medial femoral neck, pubic rami, axillary border of the scapula, ribs and posterior proximal ulna. Severe cases cause bowing, protrusio acetabuli, basilar invagination and codfish vertebrae.

Rickets is the same defect in children, expressed at the growth plate, which widens because cartilage fails to calcify. The signs are widened physes, cupping, fraying and splaying of the metaphyses (best seen at the wrist and knee), bowing of the legs once walking, the rachitic rosary (enlarged costochondral junctions), Harrison groove, frontal bossing and delayed fontanelle closure. Refer to pediatrics for laboratory confirmation and treatment.

Hyperparathyroidism and renal osteodystrophy

Primary hyperparathyroidism (usually a parathyroid adenoma) causes high calcium, low phosphate and high PTH ("stones, bones, groans and psychiatric overtones"). The pathognomonic film sign is subperiosteal bone resorption along the radial aspect of the middle phalanges of the index and middle fingers. Others are resorption of the distal clavicles, phalangeal tufts (acro osteolysis), the medial proximal tibia and the sacroiliac joints (which can look widened); salt and pepper skull from trabecular resorption; brown tumors (osteoclastomas, lytic expansile lesions that heal after treatment); loss of the lamina dura around teeth; chondrocalcinosis; and nephrocalcinosis or kidney stones.

Renal osteodystrophy is the bone disease of chronic kidney disease, combining secondary hyperparathyroidism (subperiosteal resorption, brown tumors less often), osteomalacia or rickets, osteosclerosis and soft tissue and vascular calcification. The classic spinal sign is the rugger jersey spine: broad bands of sclerosis under each end plate with lucent centers, like the horizontal stripes of a rugby shirt. Contrast this with the sharper, thinner end plate sclerosis of the sandwich vertebra in osteopetrosis.

Paget disease

Paget disease of bone is disordered remodeling with excessive osteoclastic resorption followed by chaotic osteoblastic formation, in adults over about 55, more often men, and of northern European ancestry. The pelvis is most commonly involved, then the spine, skull, femur and tibia; it may be monostotic or polyostotic. It runs in three phases: lytic (osteoporosis circumscripta of the skull; the blade of grass or flame shaped advancing lucent front in a long bone, which starts at the end of the bone and moves toward the shaft), mixed (the most common at diagnosis) and blastic (cotton wool skull, ivory vertebra). Hallmarks in every phase are bone enlargement, cortical thickening and coarsened trabeculae. In the spine the enlarged body has a thick cortical rim, the picture frame vertebra; in the pelvis there is thickening of the iliopectineal line and trabeculae. Complications include bowing and banana (transverse) fractures on the convex side, basilar invagination, deafness from skull involvement, spinal stenosis, high output heart failure, secondary osteoarthritis, and sarcomatous degeneration (under 1 percent; suspect it when pain changes or a lytic area appears). Labs show a markedly high alkaline phosphatase with normal calcium and phosphate. Refer for medical management (bisphosphonates) when symptomatic or at risk sites are involved.

Acromegaly

Acromegaly (growth hormone excess after physeal closure, usually a pituitary adenoma) causes soft tissue and bone overgrowth: heel pad thickness over about 23 mm in men (about 21.5 mm in women), spade shaped phalangeal tufts with widened bases, widened joint spaces early (cartilage hypertrophy) and premature osteoarthritis later, an enlarged sella turcica, frontal bossing, enlarged sinuses, prognathism, increased vertebral body size with posterior vertebral scalloping and thickened skin. Before physeal closure the same excess produces gigantism. Refer to endocrinology (IGF 1, glucose suppression test, pituitary MRI).

Section 5Soft tissue findings in the chest and abdomen

Why the chiropractor reads beyond the spine

Every thoracic, lumbar and rib film includes lung, heart, aorta, kidneys and abdomen. The person who orders the film is responsible for everything on it, and some of the most important findings on a spinal film are not in the bones: an aortic aneurysm on a lateral lumbar view, an apical lung tumor on a cervicothoracic film, a pneumothorax on a rib series. Read the soft tissues with a checklist every time: lungs and apices, pleura, heart and mediastinum, diaphragm and free air, aorta, kidneys and gallbladder region, and abnormal calcifications.

Lung masses and nodules

A pulmonary nodule is a rounded opacity up to 3 cm; a larger one is a mass, which is malignant until proven otherwise. Features favoring malignancy are size over about 8 mm to 1 cm, spiculated or lobulated margins, growth on comparison films, upper lobe location, smoking history and age over 40. Features favoring benignity are benign calcification patterns (central, diffuse, laminated or popcorn, the last typical of hamartoma) and no growth over 2 years. Comparison with old films is the single most useful step. Any new nodule or mass needs chest CT through the primary physician; follow up follows the Fleischner Society guidelines.

The Pancoast (superior sulcus) tumor deserves special attention because it presents as musculoskeletal pain. A lung cancer at the apex invades the brachial plexus (C8 and T1), the sympathetic chain and the upper ribs, producing shoulder and medial arm pain, weakness and wasting of the hand intrinsics, and Horner syndrome (ptosis, miosis, anhidrosis). On film, look for asymmetric apical pleural thickening over about 5 mm, an apical mass, and destruction of the posterior first to third ribs or adjacent vertebrae. Refer promptly for CT. Other chest findings that may appear include hilar enlargement (lymphoma, sarcoidosis, cancer), consolidation with air bronchograms (pneumonia) and a widened mediastinum (aortic injury after trauma, lymphoma, aneurysm).

Pneumothorax and pleural effusion

A pneumothorax is air in the pleural space. The sign is a thin white visceral pleural line with no lung markings beyond it, best seen at the apex on an upright film; an expiratory film makes a small one more obvious. On a supine film, air collects anteriorly and inferiorly, producing a deep, lucent costophrenic angle, the deep sulcus sign. Causes are spontaneous (tall, thin young men who smoke; emphysema), trauma (rib fractures) and procedures (acupuncture or dry needling over the chest wall can cause it). Tension pneumothorax shifts the mediastinum and trachea away from the affected side, flattens or inverts the hemidiaphragm, and causes hypotension and respiratory distress: call emergency services; this is a clinical emergency, not a film diagnosis. Do not confuse a skin fold (which extends beyond the chest and has lung markings beyond it) with a pleural line.

A pleural effusion is fluid in the pleural space. On the upright PA film, about 200 to 300 mL blunts the lateral costophrenic angle, while about 50 to 75 mL blunts the posterior angle on the lateral view, so the lateral is more sensitive. Larger effusions form a meniscus, a concave upper border higher laterally. A lateral decubitus film shows free fluid layering and detects as little as 5 to 10 mL; ultrasound is also excellent. Causes include heart failure (usually bilateral, right larger), pneumonia, malignancy (breast, lung, lymphoma), pulmonary embolism and trauma (hemothorax). A unilateral effusion with weight loss or a mass needs prompt workup.

Cardiomegaly and the mediastinum

The cardiothoracic ratio is the maximum transverse cardiac diameter divided by the maximum internal thoracic diameter on a PA upright film at full inspiration; over 0.5 indicates cardiomegaly. An AP or supine film magnifies the heart and cannot be used for this ratio. A poor inspiration also exaggerates heart size. Enlargement may reflect chamber dilation (heart failure, valvular disease, cardiomyopathy) or pericardial effusion, which gives a globular water bottle shape. Signs of congestive heart failure include cephalization of vessels, Kerley B lines, perihilar haze and bilateral effusions. A tortuous or dilated thoracic aorta and calcification of the aortic knob are common in older adults; a widened mediastinum after trauma suggests aortic injury.

Abdominal aortic calcification and aneurysm

The lateral lumbar film shows the abdominal aorta just anterior to the L1 to L4 vertebral bodies when its wall is calcified. Calcification itself is a marker of atherosclerosis and cardiovascular risk. An abdominal aortic aneurysm (AAA) is a diameter of 3 cm or more, usually infrarenal (below about L2), recognized when the two calcified walls are separated by more than about 3 to 3.8 cm or bow outward in a fusiform or saccular shape. Plain film cannot exclude AAA (the wall may not be calcified), so the screening test of choice is abdominal ultrasound; CT is used for surgical planning. Risk factors are age over 65, male sex, smoking, family history and hypertension; current guidance supports a one time ultrasound screen in men aged 65 to 75 who have ever smoked.

Management depends on size and symptoms:

The classic missed diagnosis is an older male smoker with deep, boring low back pain not changed by movement, a pulsatile abdominal mass, and sometimes flank or groin pain. Avoid deep abdominal soft tissue work and lumbar rotary thrust techniques over a known aneurysm, and never treat new pain in a patient with an AAA without vascular clearance.

Kidney stones, gallstones and other calcifications

Renal and ureteral calculi: about 80 to 90 percent are radiopaque (calcium oxalate and phosphate, struvite, cystine faintly); uric acid stones are radiolucent on film but visible on CT. A staghorn calculus fills the renal pelvis and calyces, usually struvite from urease producing organisms (Proteus). Ureteral stones lie along the course of the ureter (tips of the transverse processes, over the sacroiliac joint, toward the bladder) and must be distinguished from phleboliths, which are round, pelvic, smooth and have a central lucency, and lie lower and more lateral. Renal colic presents with severe colicky flank pain radiating to the groin, restlessness and hematuria; noncontrast CT is the definitive test. Fever with an obstructing stone is a urological emergency. Nephrocalcinosis (calcification of the renal parenchyma) suggests hyperparathyroidism, medullary sponge kidney or renal tubular acidosis.

Gallstones are radiopaque on film in only about 10 to 20 percent (mostly cholesterol stones, which are lucent); ultrasound is the test of choice. They lie in the right upper quadrant, often faceted with laminated rims. A porcelain gallbladder (calcified wall) carries an increased risk of carcinoma and warrants surgical referral. Right upper quadrant or right scapular pain after fatty meals suggests biliary colic.

Free intraperitoneal air (pneumoperitoneum) appears as a lucent crescent under the diaphragm on an upright chest or abdominal film, meaning a perforated viscus (ulcer, diverticulum): emergency department immediately. Dilated bowel loops with air fluid levels suggest obstruction.

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