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RADIOLOGICAL EVALUATION OF TRAUMA The radiologic modalities used in analyzing injury to the musculoskeletal system are as follows: Conventional radiography, including routine views (specific for various body parts), special views, and stress views Digital radiography, including digital subtraction arthrography and angiography (DSA) Fluoroscopy, alone or combined with videotaping Tomography (particularly trispiral tomography) Computed tomography (CT) Arthrography, tenography, and bursography Myelography and diskography Angiography (arteriography and venography) Scintigraphy (radionuclide bone scan) Magnetic resonance imaging (MRI) Radiography, Fluoroscopy, and Conventional Tomography In most instances, radiographs obtained in two orthogonal projections, usually the anteroposterior and lateral, at 90 degrees to each other are sufficient (Fig. 4.1). Occasionally, oblique and special views are necessary, particularly in evaluating fractures of complex structures such as the pelvis, elbow, wrist, and ankle (Figs. 4.2 and 4.3). Stress views are important in evaluating ligamentous tears and joint stability (Fig. 4.4). Certain special modalities are used more often in evaluating different types of injuries in specific anatomic locations. Fluoroscopy and videotaping are useful in evaluating the kinematics of joints. Tomography (zonospiral or trispiral) is useful in confirming the presence of a fracture (Figs. 4.5 and 4.6), delineating the extent of a fracture line and assessing the position of the fragments. It is also valuable in monitoring the progress of healing. Computed Tomography CT is essential in the evaluation of complex fractures, particularly in the spinal and pelvic regions (Fig. 4.7). The advantages of CT over conventional radiography are its ability to provide three-dimensional imaging, excellent contrast resolution, and accurate measurement of the tissue attenuation coefficient. The use of sagittal, coronal, and multiplanar reformation provides an adde
RADIOLOGICAL EVALUATION OF TRAUMA The radiologic modalities used in analyzing injury to the musculoskeletal system are as follows: Conventional radiography, including routine views (specific for various body parts), special views, and stress views Digital radiography, including digital subtraction arthrography and angiography (DSA) Fluoroscopy, alone or combined with videotaping Tomography (particularly trispiral tomography) Computed tomography (CT) Arthrography, tenography, and bursography Myelography and diskography Angiography (arteriography and venography) Scintigraphy (radionuclide bone scan) Magnetic resonance imaging (MRI) Radiography, Fluoroscopy, and Conventional Tomography In most instances, radiographs obtained in two orthogonal projections, usually the anteroposterior and lateral, at 90 degrees to each other are sufficient (Fig. 4.1). Occasionally, oblique and special views are necessary, particularly in evaluating fractures of complex structures such as the pelvis, elbow, wrist, and ankle (Figs. 4.2 and 4.3). Stress views are important in evaluating ligamentous tears and joint stability (Fig. 4.4). Certain special modalities are used more often in evaluating different types of injuries in specific anatomic locations. Fluoroscopy and videotaping are useful in evaluating the kinematics of joints. Tomography (zonospiral or trispiral) is useful in confirming the presence of a fracture (Figs. 4.5 and 4.6), delineating the extent of a fracture line and assessing the position of the fragments. It is also valuable in monitoring the progress of healing. Computed Tomography CT is essential in the evaluation of complex fractures, particularly in the spinal and pelvic regions (Fig. 4.7). The advantages of CT over conventional radiography are its ability to provide three-dimensional imaging, excellent contrast resolution, and accurate measurement of the tissue attenuation coefficient. The use of sagittal, coronal, and multiplanar reformation provides an adde
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BONE FORMATION AND GROWTH
BONE FORMATION AND GROWTH
The skeleton is made of cortical and cancellous bone, which are highly specialized forms of connective tissue. Each type of bony tissue has the same basic histologic structure, but the cortical
component has a solid, compact architecture interrupted only by narrow canals containing blood vessels (haversian systems), while the cancellous component consists of trabeculae separated by fatty or hematopoietic marrow. Bone is rigid calcified material and grows by the addition of new tissue to existing surfaces. The removal of unwanted bone, called simultaneous remodeling, is also a necessary component of skeletal growth. Unlike most tissues, bone grows only by apposition on the surface of an already existing substrate, such as bone or calcified cartilage. Cartilage, however, grows by interstitial cellular proliferation and matrix formation. Normal bone is formed through a combination of two processes: endochondral (enchondral) ossification and intramembranous (membranous) ossification. In general, the spongiosa develops by endochondral ossification and the cortex by intramembranous ossification. Once formed, living bone is never metabolically at rest. Beginning in the fetal period, it constantly remodels and reappropriates its minerals along lines of mechanical stress. This process continues throughout life, accelerating during infancy and adolescence. The factors controlling bone formation and resorption are still not well understood, but one fact is
clear: bone formation and bone resorption are exquisitely balanced, coupled processes that result in net bone formation equaling net bone resorption. Most of the skeleton is formed by endochondral ossification (Fig. 3.1), a highly organized process that transforms cartilage to bone and contributes mainly to increasing bone length. Endochondral ossification is responsible for the formation of all
tubular and flat bones, vertebrae, the base of the skull, the ethmoid, and the medial and lateral ends of the clavicle. For example, at approximately 7 weeks of embryonic life, cartilage cells (chondroblasts and chondrocytes) produce a hyaline cartilage model of the long tubular bones from the condensed
mesenchymal aggregate. The mechanisms leading to calcification of the cartilaginous matrix are not completely understood, but it is generally believed that the promotors of calcification are small membrane-bound vesicles known as matrix vesicles, which are present in the interstitial matrix
between the cells. At approximately the ninth week, peripheral capillaries penetrate the model, inducing the formation of osteoblasts. Osseous tissue is then deposited on the spicules of calcified cartilage matrix that remain after osteoclastic resorption, thereby transforming the primary spongiosa into secondary spongiosa.
As this process moves rapidly toward the epiphyseal ends of the cartilage model, a loose network of bony trabeculae containing cores of calcified cartilage is left behind, creating a well-defined line of advance.
This line represents the growth plate (physis) (Fig. 3.2) and the adjacent metaphysis to which the secondary spongiosa moves as it is formed. The many trabeculae of the secondary spongiosa that are resorbed soon after being formed become the marrow cavity, while other trabeculae enlarge and thicken through the apposition of new bone, although these too eventually undergo resorption and remodeling. Others extend toward the shaft and become incorporated into the developing cortex of the bone, which is formed by intramembranous ossification. At the ends of tubular bones, a similar process is initiated, creating a secondary ossification center in the epiphysis. This nucleus increases in size by the process of maturation and calcification of the cartilage surrounding the secondary center. The peripheral margin of epiphysis termed acrophysis is formed of zones of cell hypertrophy, degeneration, calcification, and ossification, similar to that of the growth plate. Endochondral bone formation is not normally observed after growth plate closure.
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IMAGING TECHNIQUES IN ORTHOPAEDICS
Use of radiologic techniques differs in evaluating the presence, type, and extent of various bone, joint, and soft-tissue abnormalities. Therefore, the radiologist and orthopedic surgeon must know the indications for use of each technique, the limitations of a particular modality, and the appropriate imaging approaches for abnormalities at specific sites. The question, “What modality should I use for this particular problem?” is frequently asked by radiologists and orthopedic surgeons alike, and although numerous algorithms are available to evaluate various problems at different anatomic sites, the answer cannot always be clearly stated. The choice of techniques for imaging bone and soft-tissue abnormalities is dictated not only by clinical presentation but also by equipment availability,
expertise, and cost. Restrictions may also be imposed by the needs of individual patients. For example, allergy to ionic or nonionic iodinated contrast agents may preclude the use of arthrography; the presence of a pacemaker would preclude the use of magnetic resonance imaging (MRI); physiologic states, such as pregnancy, preclude the use of ionized radiation, favoring, for instance, ultrasound. Time and cost consideration should discourage redundant studies. No matter what ancillary technique is used, conventional radiograph should be available for comparison. Most of the time, the choice of imaging technique is dictated by the type of suspected abnormality. For instance, if osteonecrosis is suspected after obtaining conventional radiographs, the next examination should be MRI, which detects necrotic changes in bone long before radiographs, tomography, computed
tomography (CT), or scintigraphy become positive. In evaluation of internal derangement of the knee, conventional radiographs should be obtained first and, if the abnormality is not obvious, should again be followed-up by MRI, because this modality provides exquisite contrast resolution of the bone marrow, articular cartilage, ligaments, menisci, and soft tissues. MRI and arthrography are currently the most effective procedures for evaluation of rotator cuff abnormalities, particularly when a partial or complete tear is suspected. Although ultrasonography can also detect a rotator cuff tear, its low sensitivity (68%) and low specificity (75% to 84%) make it a less definitive diagnostic
procedure. In evaluating a painful wrist, conventional radiographs and trispiral tomography should precede use of more sophisticated techniques, such as arthrotomography or CT–arthrography. MRI may also be performed; however, its sensitivity and specificity in detecting abnormalities of
triangular fibrocartilage and various intercarpal ligaments is slightly lower than that of CT arthrotomography, particularly if a three-compartment injection is used. If carpal tunnel syndrome is suspected, MRI is preferred because it provides a high-contrast difference among muscles, tendons, ligaments, and nerves. Similarly, if osteonecrosis of carpal bones is suspected and the conventional radiographs are normal, MRI would be the method of choice to demonstrate this abnormality. In evaluation of fractures and fracture healing of carpal bones, trispiral tomography and CT are the procedures of choice, preferred over MRI, because of the high degree of spatial resolution. In diagnosing bone tumors, conventional radiography and tomography are still the gold standard for diagnostic purposes. However, to evaluate the intraosseous and soft-tissue extension of tumor, they should be followed by either CT scan or MRI, with the latter modality being more accurate. To evaluate the results of radiotherapy and chemotherapy of malignant tumors, dynamic MRI using gadopentetate dimeglumine (Gd-DTPA) as a contrast enhancement is far superior to scintigraphy,
CT, or even plain MRI.
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HEPATIC CIRRHOSIS
TERMINOLOGY
Definitions
• Chronic liver disease characterized by diffuse
parenchymal
necrosis with extensive fibrosis and
regenerative nodule formation
IIMAGING
FINDINGS
General Features
• Best diagnostic clue: Nodular contour, coarse
echotexture
+/- hypoechoic
nodules
• Location: Diffuse liver involving both lobes
• Size: General atrophy with relative enlargement
of the
caudate/left lobes
• Key concepts
a Common end response of liver to a variety of insults
and injuries
a Classification of cirrhosis based on morphology,
histopathology
and etiology
a Classification
• Micronodular
(Laennec) cirrhosis
«
1 cm
diameter): Alcoholism (60-70% cases in US)
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Definition/Background
Dandy-Walker malformation is a congenital abnormality
characterized by an enlarged posterior fossa, high position of the tentorium
and torcula herophili, partial or complete absence of the cerebellar vermis,
and a cystic dilation of the fourth ventricle.
Characteristic
Clinical Features
Developmental delay and the signs and symptoms of
hydrocephalus are known presenting features.
Characteristic
Radiologic Findings
Imaging shows partial or complete hypoplasia of the
cerebellar vermis, a large fourth ventricle, a large posterior fossa, and
highly placed tentorium and torcula herophili.
Less Common
Radiologic Manifestations
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Associated central nervous system anomalies include
hydrocephalus, corpus callosum agenesis, heterotopias, schizencephaly, and
cephaloceles.
Primary Differential
Diagnoses
1-Dandy-Walker Variant
2-Mega Cisterna Magna
3-Arachnoid Cyst
Discussion of
Differential Diagnoses
Dandy-Walker Variant:
Consists of vermian hypoplasia and cystic dilation of the fourth ventricle without
enlargement of the posterior fossa.
Mega Cisterna Magna:
Consists of an enlarged cisterna magna that can result in an enlarged posterior
fossa. However, the cerebellar vermis and fourth ventricle are normal.
Arachnoid Cysts:
Sometimes can be large and result in an enlarged posterior fossa. However, the
fourth ventricle and vermis are normally formed and often displaced by the
cyst.
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Definition/Background
The Chiari II malformation is a complex anomaly with skull,
dural, brain, spine, and spinal cord manifestations. This disorder is almost
invariably associated with myelomeningocele.
Characteristic
Clinical Features
Two distinct age-dependent syndromes are identified in Chiari II malformations. One syndrome
involves infants, and the other involves older children. Signs and symptoms
during infancy include respiratory distress, difficulty swallowing, inspiratory
stridor, apnea, weakness or spasticity of the upper or lower extremities, and scoliosis.
Signs and symptoms during childhood include syncopal episodes, spastic
quadriparesis, nystagmus, weakness in upper extremities with increased tone,
and exaggerated deep-tendon reflexes.
Characteristic
Radiologic Findings
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CT and MR can both evaluate for Chiari II malformation. The
bony changes can be much better appreciated on CT scans.
Bony changes:
Small posterior fossa, concave clivus, and
petrous ridges, gaping foramen magnum, calvarial defects (Lacunar skull).
Dural changes:
Fenestrated falx.
Brain: Inferiorly
displaced, peg-shaped tonsils, towering cerebellum, cerebellum creeping around
the brain stem, beaked tectum, interdigitating gyri.
Ventricles:
Hydrocephalus, colpocephaly, and elongated and inferiorly displaced fourth
ventricle.
Spine and spinal
cord: Spina bifida, segmentation anomalies, diastomatomyelia, and
myelomeningocele.
Less Common
Radiologic Manifestations
Corpus callosal agenesis, heterotopia, and poly- microgyria.
The patient is an 8-year-old girl with spastic quadri-
paresis and exaggerated deep-tendon reflexes.
Sagittal T1WI demonstrates a relatively small posterior fossa with inferiorly displaced peg-shaped cerebellar tonsils. Also noted is concave clivus (arrow).
Axial T2WI demonstrates beaked tectum. Also noted is cerebellum creeping around the brain stem.
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Definition/Background
Chiari I malformation is defined as downward displacement of
the peg-shaped cerebellar tonsils, and sometimes the inferior vermis, through
the foramen magnum into the upper dorsal cervical canal.
Characteristic
Clinical Features
Headaches (often worsened by physical stress), ocular disturbances,
dizziness, and tremors are common presenting features. When associated with
syringohydromyelia, a sensory level can be elicited. Other associated findings
include abnormal reflexes and weakness of the extremities.
Characteristic
Radiologic Findings
Inferiorly displaced (≥5 mm), peg-shaped cerebellar tonsils,
Compression of the cerebellar cisterns. Anterior displacement of the cerebellum.
Reduced length of the clivus.
Less Common
Radiologic Manifestations
Hydrocephalus, Syringohydromyelia, Basilar invagination, Klippel-Feil
anomaly
Primary Differential
Diagnoses
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o
Downward Displacement of the Tonsils
o
Mass Lesion
o
Syringohydromyelia (Possible Etiologies)
o
Chiari I Malformation
o
Chiari II Malformation
o
Trauma
o
Intramedullary Tumors
o
Idiopathic
o
Infective Lesions, Including Arachnoiditis
o
Compressive Lesions of the Cord
o
Multiple Sclerosis
o
Communicating Hydrocephalus
Discussion of
Differential Diagnoses
Mass Lesion: The
intracranial mass lesion responsible for the downward displacement of the
tonsils will be easily identified. Also, the downward displacement of the
tonsils will not demonstrate the typical peg-shape seen in Chiari malformation.
Syringohydromyelia:
It is critical to evaluate the underlying etiology of the syrinx. The
associated findings with each of the above processes help in determining the
cause of the syrinx.
The patient is a 22-year-old man with weakness of the extremities.
Sagittal T1WI demonstrates a syrinx extending from the craniocervical junction up to the upper thoracic spine.
Sagittal T2WI demonstrates downward displacement of peg-shaped tonsils. The classic haustral pattern of the syrinx can be appreciated. Diagnosis: Chiari I malformation with syringohydromyelia.
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