We looked at the results of the different imaging modalities (Xray,
ultrasound,
CT scan and MRI) of patients with thalassemias and tried to use them to illustrate the skeletal and non-skeletal features of thalassemias.
I. Skeletal manifestations of thalassemia
The radiographic features of ß-thalassemia are due in large part to bone marrow hyperplasia that leads to various skeletal manifestations.
The skeletal system's response to this bone marrow proliferation consists of bone marrow expansion,
bone cortical thinning,
and bone resorption.
All these phenomena lead to a diffuse decrease in bone density [4].
They are easily diagnosed by X-ray.
CT scan and MRI can be helpful for a more specific diagnosis.
These alterations concern the skull,
facial bones,
vertebral column,
ribs and metaphysis of long bones [5].
A. Skull and facial bones
The transformations of the skull are represented by an enlargement of the diploë with a thinning of the inner and outer table.
The diploë's trabeculae can adopt an orientation perpendicular to the tables and form a radiative appearance known as "hair on end" (Fig.1a).
In MRI,
the thickened diploë is in hyposignal T1 and T2 compared to the gray matter signal [1].
The hyperproduction of bone marrow at the frontal,
temporal and facial bones may compromise the pneumatisation of paranasal sinuses and cause maxillary sinus filling (Fig.
1b).
The occipital bone is spared,
due to lack of hemopoietic bone marrow.
B. Spine
Marked osteoporosis and cortical thinning (Fig.
2) predispose to vertebral fractures [6].
The MRI appearance of the bone marrow is a reflection of both transfusion and chelation treatment.
Iron deposition can occur in the red marrow despite well-conducted chelation treatment [1].
Paravertebral,
mediastinal or presacral masses can be observed in relation to extramedullary hematopoiesis sites.
The epidural extension of extramedullary hematopoiesis is also possible and may be responsible for spinal compression [7].
C. Ribs
Several costal anomalies can be observed.
An enlargement of the heads and necks of the ribs at their attachment zone on the rachis is the most frequent observation.
We can also find cortical erosions through which the hematopoietic tissues spread and form an extramedullary hematopoiesis at the posterior arches (Fig.
3).
Other manifestations are osteoporosis and the "rib in the rib" aspect.
The latter is observed especially at the level of the anterior and middle arches [1].
D. Metaphyseal abnormalities
The premature fusion of growth cartilage in the long bones of the extremities in thalassemic children is common [8].
It occurs in 10-15% of cases,
and often occurs after the age of 10 years.
It mainly affects the proximal humerus and the distal femur,
typically in patients who started transfusions rather late in their management [3].
II. Non skeletal manifestations of thalassemia
Splenomegaly,
extramedullary hematopoiesis,
hemosiderosis,
and cholelithiasis are among the non-skeletal manifestations of thalassemia.
In this indication,
CT scan and MRI are the best imaging techniques as they allow diagnosis of lesionnal associations.
A. Extramedullary hematopoiesis
Extramedullary hematopoiesis is a hematopoiesis occurring outside the bone marrow.
It is a physiological phenomenon,
a reaction to chronic anemia due to bone marrow dysfunction [9].
It exists in Beta-thalassemia,
but also in sickle cell disease,
myeloproliferative syndromes,
and more rarely in Gaucher and Paget's disease.
Most often,
the extramedullary hematopoiesis is an asymptomatic,
fortuitous discovery.
Sometimes symptoms or complications may exist: chest pain,
cough,
dyspnea,
hemothorax,
pleural effusion or spinal cord compression.
It can affect several organs including the liver,
spleen and lymph nodes that are the most common locations.
Rare localizations exist such as the kidneys,
the adrenal glands,
the peritoneum,
the presacral region and the thorax.
The intrathoracic location is exceptional,
so it raises a problem of its etiological diagnosis.
Extramedullary hematopoiesis mainly affects the posterior mediastinum and thus raises a differential diagnosis with nerve tumors,
oesophageal tumors,
tuberculous abscesses or lymphomas [10].
X-rays of the thorax may show a retrocardiac lobulated mass and costal enlargement.
CT scan can shows a widening of the ribs,
paracostal sub pleural masses,
non osteolytic,
lobulated paravertebral masses,
that are well circumscribed,
uni or bilateral,
enhanced after contrast media administration (fig.
4).
Fat can be seen within the mass.
MRI reveals paravertebral masses,
of different size,
polycyclic,
arranged in rosary most often (figure 4).
B. Hepatosplenomegaly
It is due to hyperhemolysis and is characterized by myeloid metaplasia.
Splenomegaly is often homogeneous (Fig.
5).
Thalassemic patients often undergo splenectomy because of the considerable increase in the size of the spleen,
which becomes troublesome.
C. Biliary lithiasis
They are due to the accumulation of haemolytic products and are therefore common in thalassemic patients [5].
They can be diagnosed by ultrasound,
CT or MRI (Fig.
6).
They are often a fortuitous discovery in the context of an examination performed for another reason.
But,
they can also be revealed by their complications.
D. Iron overload
Hemochromatosis is an accumulation of iron in the reticuloendothelial system following polytransfusions.
It concerns the bone marrow,
liver,
heart,
spleen,
pancreas and pituitary gland [11].
MRI is a validated technique in the evaluation of hemochromatosis (Fig.
7).
It makes it possible to map the iron overload and to ensure follow-up under treatment.
The hyposignal seen in MRI is proportional to the severity of the overload [11].