13.1 Nutritional, Metabolic, Endocrine, and Hematologic Imaging Findings
Key Takeaways
- Osteoporosis is quantitative bone loss with normal mineralization (low T-score on DXA); osteomalacia/rickets is defective mineralization with Looser zones and rachitic metaphyseal changes.
- Primary hyperparathyroidism produces subperiosteal resorption (radial middle phalanges), terminal tuft resorption, salt-and-pepper skull, and brown tumors — not the uniform osteopenia of senile osteoporosis.
- Gout shows eccentric punched-out erosions with sclerotic overhanging edges (Martel sign) and preserved joint space; CPPD shows chondrocalcinosis and symmetric joint-space loss mimicking OA.
- AVN progresses from normal films (stage I) to crescent sign and femoral head collapse (stages III–IV); sickle cell disease produces H-shaped vertebral bodies and fish-mouth vertebrae.
- Acromegaly after growth-plate closure causes heel-pad thickening (>23 mm men, >21.5 mm women), tufted terminal phalanges, and widened joint spaces before secondary OA develops.
13.1 Nutritional, Metabolic, Endocrine, and Hematologic Imaging Findings
Quick Answer: Metabolic and hematologic bone disorders produce distinctive, testable radiographic patterns because each disease alters bone through a specific mechanism — quantity of bone (osteoporosis), quality of mineralization (osteomalacia/rickets), hormone-driven resorption (hyperparathyroidism), crystal deposition (gout, CPPD), or vascular insult (AVN, sickle cell). NBCE Part II Diagnostic Imaging (17% of the exam) tests whether you can match the pattern to the pathophysiology and distinguish look-alike conditions.
A Framework: Three Buckets of Metabolic Bone Disease
Most Part II metabolic-bone questions resolve when you classify the problem into one of three buckets:
- Too little normally mineralized bone — osteoporosis and glucocorticoid-induced bone loss
- Defective mineralization of bone that is present — osteomalacia (adults) and rickets (children)
- Excess resorption or abnormal deposition — hyperparathyroidism, acromegaly, gout, and CPPD
Keeping these buckets separate prevents the most common distractor pairings on the exam.
Osteoporosis and Osteomalacia/Rickets
Osteoporosis is a reduction in bone mass with a normal mineral-to-matrix ratio — the bone present is normally mineralized, there is simply too little of it. Dual-energy X-ray absorptiometry (DXA) reports a T-score (standard deviations from a young-adult reference mean):
| T-score | Classification |
|---|---|
| ≥ −1.0 | Normal |
| −1.0 to −2.5 | Osteopenia |
| ≤ −2.5 | Osteoporosis |
| ≤ −2.5 with fragility fracture | Severe osteoporosis |
Plain-film signs include cortical thinning, trabecular rarefaction, and vertebral compression fractures (anterior wedge, biconcave "fish vertebra," or burst fracture). Senile (type I) osteoporosis preferentially affects trabecular-rich sites (spine, distal radius); postmenopausal (type II) osteoporosis also involves cortical bone (hip, proximal humerus).
Osteomalacia (adults, closed physes) and rickets (children, open physes) result from defective mineralization of osteoid, most commonly from vitamin D deficiency. Adult osteomalacia mimics osteoporosis on plain film but adds Looser zones (pseudofractures) — bilateral, symmetric, incompletely mineralized lucent bands at characteristic sites (medial femoral neck, pubic rami, scapula, ribs). Rickets shows widened, cupped, frayed metaphyses with flaring ("paintbrush" appearance), delayed epiphyseal ossification, and bowing of weight-bearing long bones.
Hyperparathyroidism and Endocrine Bone Disease
Primary hyperparathyroidism drives excess osteoclastic resorption. The hallmark plain-film sign is subperiosteal bone resorption along the radial aspect of the middle phalanges of the index and middle fingers — highly specific when present. Additional findings include terminal tuft resorption (acroosteolysis), salt-and-pepper skull (granular demineralization), brown tumors (expansile lytic lesions with sclerotic margins), and chondrocalcinosis from hypercalcemia.
Acromegaly results from growth-hormone excess after epiphyseal closure. The skeleton cannot lengthen; instead, appositional overgrowth occurs. Key radiographic signs:
- Enlarged sella turcica (pituitary macroadenoma)
- Heel-pad thickness >23 mm (men) or >21.5 mm (women) on lateral foot film
- Tufting (spade-like widening) of terminal phalanges
- Widened joint spaces from cartilage overgrowth, followed by premature secondary OA
- Posterior vertebral body scalloping and prognathism
Cushing syndrome (endogenous or exogenous corticosteroids) produces disproportionate axial osteopenia — vertebral bodies demineralize more than the appendicular skeleton because trabecular bone is more glucocorticoid-sensitive. Vertebral compression fractures and rib insufficiency fractures with exuberant fluffy callus are characteristic.
Crystalline Arthropathy: Gout and CPPD
Gout (monosodium urate) classically affects the first MTP joint (podagra). Chronic tophaceous gout produces:
- Eccentric, well-marginated erosions with sclerotic borders
- Overhanging edge (Martel sign) — bony margin curling over the soft-tissue tophus
- Relative preservation of joint space until late disease
- Normal periarticular bone density (no osteopenia, unlike RA)
- Soft-tissue tophi adjacent to joints
CPPD (pseudogout) deposits calcium pyrophosphate dihydrate. The pathognomonic sign is chondrocalcinosis — fine, linear calcification within articular cartilage (knee meniscus, triangular fibrocartilage of the wrist, symphysis pubis). CPPD often mimics OA with symmetric joint-space loss, subchondral sclerosis, and cysts, but typically involves the radiocarpal and MCP joints (unlike primary OA, which spares MCPs).
Hematologic and Vascular Bone Disease
Avascular necrosis (AVN) follows interruption of blood supply. The femoral head is the most tested site. Ficat-Arlet staging:
| Stage | Plain-Film Finding |
|---|---|
| I | Normal (MRI positive) |
| II | Sclerosis, cysts; head remains round |
| III | Crescent sign (subchondral fracture), early flattening |
| IV | Collapse, secondary OA |
Causes include corticosteroids, alcohol, trauma, sickle cell disease, and idiopathic. MRI shows the double-line sign in stage II.
Sickle cell disease causes repeated microinfarcts producing H-shaped (step-like) vertebral bodies from central endplate collapse with preserved lateral corners, fish-mouth vertebrae, and AVN of the femoral and humeral heads.
Hemophilic arthropathy from recurrent hemarthroses shows enlarged epiphyses (growth-plate hyperemia), widened intercondylar notch of the knee, squaring of the patella, and subchondral cysts with preserved joint space early — distinguishing it from JIA, which causes joint-space narrowing and erosions.
Renal osteodystrophy from chronic kidney disease combines features of both osteomalacia (defective mineralization) and hyperparathyroidism (secondary hyperparathyroidism from phosphate retention and low calcitriol). The rugger-jersey spine — dense sclerotic bands at the superior and inferior vertebral endplates with a lucent mid-body — is a classic sign. Brown tumors and subperiosteal resorption may also appear.
Exam Strategy
Part II metabolic/hematologic imaging items usually present a clinical vignette (age, sex, medications, joint distribution) plus a described radiographic finding. Match the finding to the mechanism: subperiosteal resorption = hyperparathyroidism; chondrocalcinosis = CPPD; overhanging erosions = gout; crescent sign = AVN; Looser zones = osteomalacia. When two conditions share osteopenia, look for the distinguishing sign rather than the shared feature.
Bilateral, symmetric lucent bands at the medial femoral necks and pubic rami are most consistent with which condition?
A hand radiograph shows subperiosteal bone resorption along the radial aspect of the middle phalanges. This finding is most specific for:
A knee radiograph shows thin, linear calcification within the meniscus and symmetric joint-space narrowing with subchondral sclerosis. The most likely diagnosis is:
A lateral foot radiograph in a 45-year-old man with enlarged hands and jaw shows a heel-pad thickness of 26 mm. This finding is most consistent with: