RADIOLOGICAL EVALUATION OF TRAUMA



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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
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BONE FORMATION AND GROWTH



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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



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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



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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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Dandy Walker Malformation



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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Chiari II malformation



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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Chiari 1 Malformation



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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Schizencephaly



Definition/Background
Schizencephaly is a gray matter-lined, cerebrospinal fluid-filled cleft that extends from the ependymal lining of the ventricle to the pia of the overlying cerebral cortex. The clefts can be unilateral or bilateral, and can occur anywhere in the brain. There are two types of schizen-cephaly: type I, or closed-lip schizencephaly, in which the cleft walls are in apposition; and type II, or open-lip schizencephaly, in which the walls are separated.
Characteristic Clinical Features
Clinical features of schizencephaly are highly variable. Patients with unilateral clefts with fused lips may have mild hemiparesis and seizures but otherwise have normal development. When the cleft is open, patients present with mild-to-moderate developmental delay and hemiparesis; severity is related to the extent of cortex involved in the defect. Patients with bilateral clefts present with severe mental deficits and severe motor anomalies, including spastic quadriparesis.
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Characteristic Radiologic Findings
CT and MR can be used to evaluate for schizencephaly. Multiplanar capability of MR and its inherently better soft-tissue resolution makes it a better imaging modality to evaluate for shizencephaly.
A gray matter–lined cerebrospinal fluid-filled cleft is seen to extend from the ependymal lining of the ventricle to the pial surface of the brain. A characteristic feature of such clefts is a slight outpouching or “nipple” along the ependymal surface of the cleft. This is most often seen with closed lip, or minimally open lip, schizencephaly. The gray matter lining the cleft is always abnormal, and frequently demonstrates a nodular gyral pattern.
Less Common Radiologic Manifestations
A large percentage of patients with schizophrenia present with an absent septum pellucidum. Almost half of such patients exhibit optic nerve hypoplasia. The neuroradiologist should therefore evaluate for septo-optic dysplasia in patients with schizencephaly.Mild hypoplasia of the corpus callosum is commonly seen.
Primary Differential Diagnosis
1-Porencephalic Cyst
Discussion of Differential Diagnosis

Porencephalic Cyst: Cerebrospinal fluid-filled cyst lined by gliotic white matter and not gray matter.

The patient is a 16-year-old boy with seizures.

 Axial  CT  scan  demonstrates  a  deep  gray  matter–lined (arrowheads) cleft extending from the pia of the overlying cerebral cortex to the ependymal lining of the ventricle. 


At a slightly caudal level, axial CT scan demonstrates a slight outpouching or “nipple” (arrow) along the ependymal surface of the cleft. Diagnosis: Closed-lip schizencephaly. 

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Polymicrogyria



Definition/Background
Polymicrogyria is a cerebral cortical malformation characterized by interruption of the normal cortical development during the late stages of neuronal migration and cortical organization. This results in abnormal development of the deeper layers of the cortex, with multiple small gyri and shallow cortical sulci.
Characteristic Clinical Features
Clinical features include developmental delay, and seizures.
Associations: Congenital cytomegalovirus infection, in utero ischemia, and chromosomal mutations (mutations of Xq28, 16q12.2-21).
Syndromic associations: Congenital bilateral perisylvian syndrome and Aicardi syndrome.
Characteristic Radiologic Findings
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MR imaging is the gold standard to evaluate for polymicrogyria. 3DFT spoiled gradient acquisition (T1W)  analyzed in at least two imaging planes is essential. The typical imaging appearance is of small irregular cortical gyri with shallow or absent sulci. Occasionally, a thick, bumpy cortex is seen. Perisylvian cortex is the most common location, although any area of the cerebral cortex can be involved. Usually focal, unilateral; multifo-cal; bilateral, asymmetrical; or bilateral, symmetrical forms have been described. Bilateral involvement is often syndromic.
Primary Differential Diagnosis
1-Pachygyria
Discussion of Differential Diagnosis
Pachygyria: Characterized by a broad thick gyrus and does not demonstrate the typical irregular, bumpy  cortical surface noted in polymicrogyria. However, sometimes it can be difficult to distinguish the two entities.

The patient is a 14-year-old boy with developmental delay.


Coronal  3DFT  SPGR  sequence  demonstrates shallow, absent cortical sulci in the left perisylvian region. 

 Axial 3DFT SPGR sequence demonstrates a bumpy left perisylvian cortex.

 Sagittal 3DFT SPGR sequence demonstrates a thickened cortex with small irregular cortical gyri and absent sulci involving predominantly the frontal operculum in the left perisylvian region. Diagnosis: Polymicrogyria. 



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Cavum Septum Pellucidum



Definition/Background
Cavum septi pellucidi (CSP) and cavum vergae (CV) represent collections of cerebrospinal fluid (CSF) between the leaves of septum pellucidum and have been mis-named as the fifth and sixth ventricles. CSP is a constant feature in the human fetus and usually gets obliterated toward term. However, persistence is relatively common, and has been reported in 20% of brain autopsies. CV is a posterior extension of CSP and is never described alone.
Characteristic Clinical Features
CSP and CV are usually asymptomatic.
Characteristic Radiologic Findings
Both CT and MR demonstrate nonenhancing CSF-filled midline cavities bounded superiorly by the corpus  callosum and laterally by the leaves of the septum pellucidum and the fornices. There is no communication with the lateral ventricles.
Primary Differential Diagnoses
1.       Cavum Velum Interpositum (CVI)
2.       Arachnoid Cyst
3.       Epidermoid Cyst
Discussion of Differential Diagnoses
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Cavum Velum Interpositum (CVI): Typically triangular, nonenhancing CSF-filled midline cavity will be seen within the cistern of velum interpositum at the level of the bodies of the lateral ventricles. CVI does not extend anteriorly into the region of the frontal horns of the lateral ventricles.
Arachnoid Cyst: Based on imaging alone, it can be difficult to distinguish an arachnoid cyst from CSP or CV. Presence of hydrocephalus should favor arachnoid cyst; also, it should be noted that midline CSF-containing cysts should favor CSP, CV, or CVI, or, less likely, an arachnoid cyst.

Epidermoid Cyst: Diffusion restriction will be seen.

The patient is a 42-year-old man with change in mental status.

Axial  T2WI  at  the  level  of  the  frontal horns demonstrates cerebrospinal fluid (CSF)between the leaves of the septum pellucidum suggestive of cavum septi pellucidi.


                       
 Axial T2WI at the level of the body of the lateral ventricle demonstrates cerebrospinal fluid (CSF) between the leaves of the septum pellucidum suggestive of cavum septi vergae. 

 Sagittal T1WI in a different patient demonstrates upward bowing of the fornix (arrowhead) and downward displacement of the internal cerebral vein (arrow). Diagnosis: Cavum septi pellucidi and vergae. 

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Agenesis of Corpus Collosum



Definition/Background
Agenesis of the corpus callosum is a rare congenital disorder in which there is partial or complete absence of the corpus callosum. It is usually a sporadic occurrence, but is known to be associated with trisomy 18, trisomy 13, and trisomy 8.
Characteristic Clinical Features
Signs and symptoms of agenesis of corpus callosum vary greatly among individuals. Some common characteristics include vision impairment, delayed milestones, and hypotonia.
Characteristic Radiologic Findings
Though the diagnosis of agenesis of the corpus callosum can be easily established on CT studies, MR with its multiplanar capability and inherently superior soft-tissue resolution is better at demonstrating the imaging features of agenesis of the corpus callosum.
■ Parallel, nonconverging lateral ventricles, best appreciated on axial scans
■ High-riding third ventricle, which may be open superiorly to an inter-hemispheric cyst, best appre-
ciated on coronal images
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■ Indentation on the medial aspect of the frontal horns by Probst bundles (longitudinally oriented fiber tracts) resulting in the “Viking horns” or “bull’s horns” appearance, best appreciated on coronal images
■ Dilated occipital horns (Colpocephaly), best appre-ciated on axial or coronal images
■ Radial, spokelike orientation of the gyri, best appre-ciated on sagittal T1WI
Associated findings:
■ Lipoma of the corpus callosum (midline)
■ Azygous anterior cerebral artery
■ Chiai II malformation
■ Migration disorders
■ Cephaloceles (usually midline)
■ Dandy-Walker malformation
■ Holoprosencephaly
■ Median cleft syndrome

Note: Diagnosis of agenesis of corpus callosum can be established on prenatal sonogram or MRI studies.

The patient is a 42-year-old, with change in mental status.


Axial CT scan demonstrates parallel, nonconverging lateral ventricles. Also noted are dilated occipital horns suggestive of colpocephaly.

 Axial CT scan demonstrates high-riding third ventricle. 

Reformatted coronal CT scan demonstrates indentation on the medial aspect of the frontal horns by Probst bundles, resulting in “bull’s horns” appearance. 

 Reformatted  mid-sagittal  CT  scan  demonstrates  absent corpus callosum. This results in radial, spoke-wheel-like orientation of the gyri. Diagnosis: Agenesis of corpus callosum.

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Lobar Holoprosencephaly



The patient is a 5-month-old infant with hypotelorism, a cleft palate, and delayed milestones.
Definition/Background
Holoprosencephaly (HPE) is a complex group of malformation disorders characterized by a failure of differentiation and cleavage of the prosencephalon, occurring between the 18th and the 28th day of gestation, and affecting both the forebrain and the face. HPE has been associated with both teratogenic (such as maternal diabetes) and genetic causes. Sonic hedgehog (SHH), ZIC2, SIX3, TGIF, PTCH, GLI2, and TDGF1 genes have been positively implicated in HPE. This disorder can also be due to chromosomal abnormalities, with a higher prevalence observed in trisomy 13 (Patau’s syndrome), and less commonly in trisomy 18 (Edward’s syndrome) and triploidy. Classically, three levels of increasing severity are described: lobar, semilobar, and alobar. Another milder subtype of HPE, the middle inter-hemispheric variant (MIH), or syntelencephaly, has also been recognized.
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Characteristic Clinical Features
HPE is generally associated with craniofacial anomalies, such as hypotelorism, midline cleft lip and/or palate, cebocephaly (flattened nose with single nostril), single maxillary central incisor and microcephaly. In severe cases, anophthalmia, cyclopia, or proboscis (ethmocephaly), can be present. The most common neurologic sign is developmental delay. Other commonly seen signs include mental retardation, epilepsy, weakness, spasticity, dystonia, and choreoathetosis. Endocrine disorders (diabetes insipidus or growth hormone deficiency), oro-motor dysfunction (feeding and swallowing difficulties) and autonomic dysfunction (instability of temperature, heart, and/or breath rate) may also be seen. Usually the degree of craniofacial and neurologic abnormalities cor-relates with the severity of the brain malformation.
Characteristic Radiologic Findings
Alobar Holoprosencephaly: Presents a pancake-like cerebrum, without interhemispheric division; large monoventricle that can communicate with a dorsal cyst; absence of olfactory bulbs and tracts (arrhinen-cephaly); absence of corpus callosum; and fusion of deep gray nuclei.
Semilobar Holoprosencephaly: Shows rudimentary cerebral lobes, with incomplete interhemispheric division (IHF and falx present posteriorly only); presence of posterior ventricle horns with small third ventricle; absence or hypoplasia of olfactory bulbs and tracts; presence of splenium of corpus callosum; partial fusion of thalami and basal ganglia; and dorsal cyst.Lobar Holoprosencephaly: Presents with almost normal lobar differentiation and separation of the hemispheres, with the exception of midline continuity of the basal frontal cortex; IHF and falx hypoplastic anteriorly and presenting posteriorly; rudimentary anterior horns of the ventricles; presence of splenium of corpus callosum, and variable presence of anterior body with hypoplasia of the genu of corpus callosum; usually fully separated thalami; and variable degree of fusion of the basal ganglia.
Middle Interhemispheric Variant of Holoprosencephaly (MIH): Shows failure of separation of the posterior frontal and parietal lobes; normal or hypoplasic ante-rior horns; presence of genu and splenium of corpus callosum with absence of callosal body; fully separated hypothalamus and basal ganglia; and variable fusion of thalami. Cortical dysplasia and heterotopic gray matter are also common findings.
Primary Differential Diagnosis
1-Septo-Optic Dysplasia
Discussion of Differential Diagnosis

Septo-Optic Dysplasia (SOD): Consists of hypoplasia of the optic nerves and hypoplasia or absence of the septum pellucidum. Schizencephaly and gray matter heterotopias may be present. However, some authors consider that some patients with SOD have a mild form of holoprosencephaly.




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Cephalocele



DEMOGRAPHICS/CLINICAL HISTORY
The patient is an 18-month-old boy with developmental delay.
DISCUSSION
Definition and Background
Cephaloceles (encephaloceles) encompass all neural tube defects that result in abnormal herniation of intracranial structures through mesodermal defects. They can be divided into meningoceles and meningoencephaloceles, depending on whether there is a neural component within the herniation. The herniating brain is often abnormal.Encephaloceles can be divided into the anterior (sincipital), basal, and posterior (occipital) types. Sincipital (also called frontoethmoidal type) encephaloceles represent herniation towards the soft tissues of the forehead, external nose, and orbit. These are particularly common in Southeast Asia, and are further classified as nasofrontal, nasoethmoidal, and nasoorbital (anterior and posterior orbital), named according to the bones at the superior and inferior margins of the defect.Basal encephaloceles protrude through defects in the basal skull bones (anterior and central skull base) and can be subdivided into the transethmoidal, sphenoethmoidal, sphenomaxillary, spheno-orbital, and transsphenoidal subtypes.Posterior encephaloceles are occipital or craniocervical in location, with defects located in the occipital bone, and posterior arch of atlas. These are often associated with a hindbrain abnormality.Rare varieties include the convexity encephaloceles, including the atretic cephaloceles.
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Characteristic Clinical Features:
Most anterior (frontoethmoidal) and posterior (occipital) encephaloceles are usually diagnosed at birth, if  not diagnosed antenatally. These often present as a skin-covered mass, although some atretic cephaloceles over the convexity may not be diagnosed till much later in life. If the encephalocele is not skin-covered, it is treated as a neurosurgical emergency at birth.Basal cephaloceles may present as an intranasal  or nasopharyngeal mass with nasal obstruction, or  with symptoms of complications such as CSF leaks  (CSF rhinorrhea) or recurrent meningitis, or epilepsy. Nasal meningoencephaloceles may change in size in response to the Valsalva maneuver and will transillumi-nate. Hydrocephalus may occur.Posterior encephaloceles are associated with higher risk of hydrocephalus and seizures, the determinants of overall prognosis.
Characteristic Radiologic Findings
In general, encephaloceles are associated with defects in the cranium or the skull base that may be best defined by CT, further enhanced with 3D rendering. Evaluation of the contents of the herniation and the brain parenchyma, and any associated anomalies, is best performed with MRI.
It is useful to remember that the structures of the anterior skull base including the cribriform plate may be partially or incompletely ossified till about 2 years of age.Posterior encephaloceles may be associated with Chiari and Dandy-Walker malformations.
Primary Differential Diagnoses
1-Nasal Dermoid
2-Nasal Glioma
Discussion of Differential Diagnoses
Nasal Dermoid: The most common nasal abnormalities, presenting as a midline mass without or with a sinus tract. External opening may show a tuft of hair.

Nasal Glioma: Midline, firm, nasal or nasopharyngeal mass consisting of glial tissue that could be considered a variant of an encephalocele, although no skull base defect may be demonstrable.



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