Marrow Disorders

Routine radiographs

Radionuclide scans

Magnetic resonance imaging (MRI)

Bone marrow consists of trabeculae (15%)
and cellular constituents (85%) (erythrocytic, leukocytic, fat cells,
and reticulum cells).

Hemopoietic cells (blood cells) comprise red marrow. The remainder, or inactive marrow, is yellow marrow.

Red marrow is 40% water, 40% fat, and 20% protein. Yellow marrow is 80% fat, 15% water, and 5% protein.

At birth, nearly the entire skeleton is
composed of red marrow. Red marrow converts to yellow marrow in a
predictable pattern from peripheral to central. The adult marrow
pattern is usually attained by 25 years of age.

Adult marrow pattern is primarily red in
the axial skeleton (skull, spine, pelvis, ribs, and sternum) and
proximal humeri and femora.

MRI features of normal marrow are
predictable on T1- and T2-weighted sequences. Yellow marrow has signal
intensity similar to subcutaneous fat on T1-weighted sequences and low
signal intensity on T2-weighted sequences. Red marrow has lower
intensity than fat on T1-weighted and signal intensity near that of fat
(high) on T2-weighted sequences. STIR sequences show red marrow as even
higher intensity compared with T2-weighted sequences.

Hematopoietic demand may result in conversion of yellow to red marrow.

The sequence of red marrow conversion
occurs in reverse of the red to yellow marrow conversion, occurring as
one develops adult marrow pattern.

Reconversion begins in the axial skeleton and moves peripherally.

Reconversion is symmetric, but not necessarily uniform.

Patients without bone marrow disorders may develop expanded red marrow termed “hyperplasia.”

Marrow reconversion, or hyperplasia, may be the result of multiple conditions:

Imaging of red marrow reconversion is
best accomplished with MRI. Signal intensity changes may be difficult
to differentiate from infiltrative diseases. T1-weighted images show
areas of decreased signal intensity. T2-weighted and STIR sequences
show signal intensity higher than fat.

In patients with myeloid depletion, the hemopoietic (red) marrow is replaced by fatty (yellow) marrow.

Fat replacement may be diffuse or focal, depending on the extent and duration of the process.

Conditions leading to myeloid depletion include

Radiation changes are focal, so fat
replacement occurs in the treated region. Changes occur as early as 3
to 7 weeks. With low doses, recovery may occur. Patients receiving more
than 50 Gy usually are irreversible.

Fatty marrow has fat signal intensity on T1- and T2-weighted sequences.

Bone marrow ischemic changes usually are focal (see Chapters 4, 5, and 7).

Causes of bone marrow ischemia and osteonecrosis are numerous.

Focal changes are most common in the hip, knee, and shoulder.

Avascular necrosis occurs in the subchondral epiphysis, and bone infarction occurs in the metaphysis and diaphysis.

Image changes may be evident on
radiographs in advanced cases. MRI is the technique of choice for
imaging early ischemic changes. Contrast-enhanced images are useful to
evaluate subtle changes in flow.

There are numerous marrow infiltrative
processes, including inflammatory conditions, neoplastic processes
(metastasis, myeloma), lipidosis, histiocytosis, and
hyperlipoproteinemias.

Table 12-1 summarizes infiltrative marrow conditions.

Routine radiographs may demonstrate marrow expansion, lytic lesions, sclerotic lesions, or mixed lytic and sclerotic changes.

MR images demonstrate low signal
intensity on T1-weighted sequences and increased signal on T2-weighted
or STIR sequences in most cases. Contrast enhancement is variable and
nonspecific.

There are multiple lipidoses. The more common disorders are listed in Table 12-1.

Gaucher disease is a rare familial
disorder of cerebroside metabolism resulting in lipid accumulation in
reticuloendothelial cells. The condition affects males and females in
childhood or early adulthood. Patients present with hepatosplenomegaly.
Infiltration occurs in other regions, including marrow. Radiographs
demonstrate marrow expansion, endosteal scalloping, osteonecrosis, and
pathologic fractures. Changes are most common in the axial skeleton and
proximal long bones. MR images demonstrate decreased signal intensity
on T1- and T2-weighted sequences because of fibrosis and
glucocerebroside deposition.

Niemann-Pick disease is a rare genetic
disorder with deposition of sphingomyelin in the reticuloendothelial
system. Males and females are equally affected. Many are Jewish.

There is an acute fatal type and chronic
forms with and without central nervous system involvement. Most
patients present in infancy with jaundice and hepatosplenomegaly.

Radiographic features are similar to those for Gaucher disease.

Fabry disease is a hereditary sex-linked disorder with deposition of ceramide trihexoside.

Patients present with skin lesions,
fever, pain, and paresthesias. Patients may die in later adult life
because of renal or cardiac involvement. Radiographic features include
periarticular swelling and avascular necrosis.

Gangliosidosis is an inherited liposomal
storage disorder caused by lack of ganglioside β-galactosidase.
Ganglioside accumulates in the nervous system and other tissues.
Clinical features include mental retardation, a cherry spot in the
retina, hepatomegaly, and bony abnormalities. Radiographic features
include osteopenia, delayed bone maturation, thickened calvarium,
horizontal ribs, flattening of vertebral bodies, flared iliac, and thin
long bones.

Three conditions constitute Langerhans cell histiocytosis (histiocytosis X): (i) eosinophilic granuloma (see Chapter 10), (ii) Hand-Schüller-Christian disease, and (iii) Letterer-Siwe disease.

Common to all is the presence of Langerhans cells containing cytoplasmic inclusion bodies.

Eosinophilic granuloma is the mildest form presenting with single or multiple bone lesions.

Hand-Schüller-Christian disease presents
with diabetes insipidus, exophthalmus, and single or multiple bone
lesions. This condition is most common in children. Multisystem
involvement includes otitis media, skin lesions, hepatosplenomegaly,
and anemia. Neural, lung, and renal involvement are common. Skeletal
lesions are similar to eosinophilic granuloma, but more disseminated.
The disease is fatal in up to 30% of cases.

Letterer-Siwe disease is an acute
disorder common in children younger than 3 years. Multisystem
involvement (liver, spleen, skin, anemia) is typical. Most patients
survive only 1 to 2 years. Radiographically, there are multiple lytic
lesions, most commonly involving the skull.

Erdheim-Chester disease is a disorder of adults (both male and female).

Hyperlipoproteinemias present with increased plasma cholesterol and triglycerides. Five types are described.

Radiographic features include

Myelofibrosis is an uncommon disorder resulting in fibrous replacement of marrow and extramedullary hematopoiesis.

Patients typically are middle-aged or elderly and present with fatigue, hepatosplenomegaly, and purpura.

Secondary gout is evident in 5% to 20%.

Radiographic features include bone sclerosis and splenomegaly.

MR images demonstrate low signal intensity on T1- and T2-weighted sequences.

Differential diagnosis includes Paget disease and metastasis.

Vertebral compression fractures are common, especially in elderly females.

Differentiation of traumatic or
osteopenic compression fractures from metastasis or myeloma may be
difficult with conventional imaging studies (radiographs, radionuclide
scans).

MRI is more useful for differentiating
compression fractures caused by osteopenia or trauma from malignancy.
MR features suggesting malignancy:

Benign MR features: