Radiological Findings (Untreated)
Massive proliferation of hematopoietic tissue leads to bone expansion and cortical thinning. These changes affect both the axial and appendicular skeleton.
- Skull and Facial Skeleton: The diploë of the cranial vault widens (except for the occipital bone). The earliest changes in the frontal bone form the classic «hair-on-end» sign (hair-on-end). Paranasal sinuses fail to develop due to bone marrow infiltration, resulting in malocclusion and a «rodent facies» appearance. Meanwhile, the ethmoid air cells remain intact as they contain no red bone marrow.
- Tubular Bones: Long bones develop a characteristic deformation—the «Erlenmeyer flask» sign. In the phalanges and metacarpals, trabeculae first thin and then coarsen due to newly formed tissue. Bones acquire a cylindrical or biconvex shape.
- Axial Skeleton: The ribs exhibit club-like thickening of their anterior ends and the «rib-within-a-rib» sign (subperiosteal spread of hematopoietic tissue). The spine develops generalized osteopenia, leading to compression fractures, scoliosis, and biconcave vertebrae.
- Growth Plates: Due to premature closure of growth plates (most commonly in the humerus and femur), short stature may develop in patients older than 10 years.
Extramedullary Hematopoiesis (EMH)
In patients with severe disease who survive into adulthood, foci of hematopoiesis form outside the bone marrow.
- Localization: EMH most commonly develops in the thoracic paraspinal region (spreading from adjacent ribs), the mediastinum, and the presacral zone.
- Complications: Epidural spread of paraspinal masses poses a direct threat of spinal cord compression.
- Imaging Findings: MRI is the diagnostic method of choice. Due to bone marrow reconversion, T1-weighted images reveal a diffuse decrease in signal intensity from bone structures.
Transfusion-Related Complications
Modern treatment prevents severe bone deformations but creates new problems. Repeated transfusions lead to iron overload and hyperuricemia.
- Joint Involvement: Excess iron damages the synovial membrane and articular cartilage. Radiologically, this manifests as symmetrical joint space narrowing, cyst formation, osteophytes, and subchondral collapse. Chondrocalcinosis of large joints and signs of gout are characteristic.
- Bone Involvement: Iron deposition exacerbates osteoporosis (detected in 13.6–50% of patients even with good treatment) and increases the risk of osteonecrosis and osteomyelitis.
- MRI Findings of Tissue Siderosis: Excess iron causes a marked decrease in signal intensity, which is particularly well visualized on T2-weighted and gradient echo sequences.
Side Effects of Chelation and Concomitant Therapy
Drugs used for iron removal (chelators) and osteoporosis treatment have their own specific radiological complication patterns.
- Deferoxamine: Can cause growth retardation and bone dysplasia (risk is higher if treatment starts before age 3). Radiographs show irregularities of the metadiaphyseal junction, dense sclerotic bands resembling «flame-like» zones, and widening of the metaphyses and growth plates. This can be complicated by slipped capital femoral epiphysis, genu varum/valgum, and platyspondyly (flattening of the vertebrae).
- Deferiprone: Associated with the development of arthropathy, most commonly affecting the knee joints. MRI clearly visualizes joint effusion and synovitis. A chronic course leads to flattening of the femoral condyles, patella, and tibial plateau.
- Bisphosphonates: Used to treat concomitant osteoporosis, but their use carries the risk of atypical femoral fractures.
Briefly: answers to topical questions
What MRI signal characteristics are typical for the soft tissue lesions of extramedullary hematopoiesis?
Soft tissue lesions of extramedullary hematopoiesis are characterized by heterogeneous signal intensity on tomograms.
- Heterogeneous Intensity — the masses themselves show an inhomogeneous signal on T1- and T2-weighted images.
- Process Inactivity — determined by the presence of fat tissue signal within the lesions.
- Process Activity — confirmed if contrast enhancement (enhancement) is observed.
What radiological signs are characteristic of abdominal parenchymal organ involvement in beta-thalassemia?
The main manifestations of abdominal parenchymal organ involvement are massive hepatosplenomegaly and tissue siderosis.
- Hepatosplenomegaly — a significant enlargement of the liver and spleen occurring as a reaction to severe anemia and activation of extramedullary hematopoiesis.
- Tissue Siderosis — iron overload of organs secondary to regular hypertransfusions.
Magnetic resonance imaging (MRI) is used for radiological assessment of the severity of tissue siderosis.
To remember the classic radiological triad of untreated thalassemia: «Hair-on-head, Flask in legs, Rib in rib» (hair-on-end sign on the cranial vault; Erlenmeyer flask in long bones; subperiosteal growth in ribs).
Class and exam questions
Why do bone deformations in thalassemia rarely manifest in infants under 6 months of age?
In the first months of life, the infant is protected by high levels of fetal hemoglobin (HbF), which suppresses the development of severe anemia and, consequently, bone marrow hyperplasia.
Why do the ethmoid air cells remain unaffected during the development of «rodent facies»?
Unlike other paranasal sinuses, the ethmoid air cells remain intact because they initially contain no red bone marrow and do not undergo hyperplasia.
What metaphyseal changes are characteristic of deferoxamine toxicity?
Radiographs show irregularities of the growth plates and dense sclerotic metaphyseal bands extending toward the diaphysis in a «flame-like» pattern.
What else to study on this topic
- Pathophysiology of extramedullary hematopoiesis development and methods of its radiological staging.
- Endocrine complications of iron overload (hypogonadism, growth hormone deficiency, hypothyroidism).
- Comparison of radiological findings in thalassemia and sickle cell disease.
- The role of MRI in the quantitative assessment of liver and myocardial tissue siderosis in hypertransfusion therapy.
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