General radiological signs of haemoglobinopathies
The main haemoglobinopathies include thalassaemias (thalassaemias) and sickle cell disease (sickle cell disease — SCD).
Radiological changes in these conditions are secondary and result from bone marrow hyperplasia attempting to compensate for chronic erythrocyte deficiency. On imaging, this manifests as:
- general bone expansion;
- marked cortical thinning;
- diffuse osteopenia.
On MRI T1-weighted images, a diffuse decrease in bone marrow signal intensity is observed.
Additional radiological findings may indicate the consequences of specific treatment (e.g., hypertransfusion or iron chelation) or severe complications of the disease itself, such as osteonecrosis.
Sickle cell anaemia and osteomyelitis
Patients with sickle cell anaemia are at high risk of developing bone infections. Osteomyelitis (osteomyelitis) has a characteristic imaging appearance.
- Radiography: acute osteomyelitis is visualized as an ill-defined lytic lesion, typically located in the metaphysis (e.g., the distal third of the tibia). The process is accompanied by prominent periostitis.
- MRI (STIR sequence): reveals an irregularly shaped bone abscess. It is often seen communicating with an adjacent soft-tissue abscess through a cortical defect. Bone marrow edema, periosteal stripping, and peripheral contrast enhancement of the lesion are also noted.
- Ultrasound: plays a key role in confirming the infectious nature of the process. It is used to perform targeted aspiration of fluid from subperiosteal collections. Notably, such fluid collections occur in over 80% of osteomyelitis cases, but are completely absent in acute bone infarction.
Blood coagulation disorders (Coagulopathies)
Although coagulopathies have a different aetiology, they are closely linked to haematological skeletal disorders. There are three main inherited disorders that present an identical radiological picture, differing only in severity.
- Classic haemophilia (Haemophilia A / Haemophilia A): X-linked recessive disorder due to factor VIII deficiency. Occurs with a frequency of 1:5,000. Bleeding starts in the first year of life after minimal trauma. Haemarthrosis (haemarthrosis) already develops in 70% of children under 2 years of age.
- Christmas disease (Haemophilia B / Christmas Disease): X-linked factor IX deficiency. Prevalence is 1:30,000, presenting milder than the classic form.
- Von Willebrand disease (Von Willebrand Disease): Autosomal dominant inheritance, affecting both sexes. Combines a capillary defect with factor VIII deficiency. Usually mild and rarely leads to severe bone abnormalities.
Soft tissue haemorrhages in these patients can lead to the formation of a so-called haemophilic pseudotumour (*haemophilic pseudotumour), which is frequently localised near muscle attachment sites.*
Haemophilic arthropathy: pathogenesis and imaging
In severe haemophilia, the vast majority of bleeding episodes (85–90%) occur into joints—most commonly affecting the knees, elbows, ankles, hips, and shoulders.
Acute haemarthrosis appears on radiographs as a tense intra-articular effusion. MRI is the gold standard for early detection of blood in the joint. If episodes recur, haemophilic arthropathy (haemophilic arthropathy) develops.
Mechanism of joint destruction: Blood penetrates the synovial membrane and joint cavity, causing chronic haemorrhagic synovitis and cartilage degradation. The resulting local hyperaemia (hyperaemia) provokes:
- periarticular osteopenia;
- epiphyseal overgrowth (epiphyseal overgrowth);
- premature closure of growth plates.
Similar to rheumatoid arthritis, a pannus forms, causing marginal erosions. The trabecular bone pattern becomes coarse due to the loss of secondary trabeculae. Episodic exacerbations leave a trace in the form of growth arrest lines.
Due to haemorrhages, subarticular cysts (subarticular cysts) appear within bones, posing a risk of subchondral collapse. Soft tissues around the joint appear denser on radiographs as a result of synovial thickening and local accumulation of haemosiderin-laden (haemosiderin) macrophages.
Briefly: answers to topical questions
How does the "fish vertebra" sign (H-shaped vertebrae) form in sickle cell anaemia?
The "H-shaped" vertebra is formed due to focal collapse of the central part of the vertebral body endplate resulting from infarction.
- Cause — venous thromboembolism in the center of the vertebral endplate.
- Radiograph — appears as a "stepped depression" of the endplates.
- Healing — the floor of the depression forms a flat sclerotic rim.
- Diagnostic value — the sign is nearly pathognomonic for sickle cell anaemia, but occasionally occurs in Gaucher disease.
The adjacent vertebra compensatorily increases in height — the "tower" vertebra.
In which bones does avascular osteonecrosis most frequently develop in sickle cell anaemia?
Avascular necrosis in sickle cell anaemia most frequently affects the epiphyses of the femoral and humeral heads, often bilaterally.
- Femoral head (caput femoris) — typical location, especially in the HbS-C variant.
- Humeral head (caput humeri) — also a characteristic site of involvement.
In the HbS-C variant, bone infarctions (especially of the femoral head) occur 5 times more frequently than in the homozygous HbS-S form. Osteonecrosis develops in patients by the age of 35.
To remember the most frequent sites of involvement in haemophilia (K-L-G-T-P), use the mnemonic: Knee, Elbow, Ankle, Hip, Shoulder.
Class and exam questions
How to differentiate osteomyelitis from bone infarction on ultrasound in sickle cell anaemia?
In osteomyelitis, ultrasound shows subperiosteal fluid collections in 80% of cases, which are never seen in acute bone infarction.
Why does epiphyseal overgrowth occur in haemophilic arthropathy?
Chronic haemorrhagic synovitis leads to persistent local hyperaemia, which stimulates accelerated bone tissue growth in the epiphyseal region and early closure of growth plates.
What is the main difference in the inheritance pattern between hemophilia A and von Willebrand disease?
Haemophilia A is an X-linked recessive disorder (affecting predominantly males), while von Willebrand disease is inherited dominantly and affects both sexes.
What else to study on this topic
- Pathophysiology of haemophilic pseudotumour development
- Specifics of the MRI appearance of haemosiderin deposition in the synovial membrane
- Differential diagnosis of subchondral collapse and avascular necrosis
- The role of iron chelation and its effect on the skeletal system
- Features of surgical management of contractures in haemophilic arthropathy
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