Книги по МРТ КТ на английском языке / Neurosurgery Fundamentals Agarval 1 ed 2019

e)  Primary motor cortex—corona ra- diata—internal capsule—cerebral pe- duncle—anterior pons—pyramids— spinal cord

4.Which of the following is correct regarding the interventricular foramen, also known as foramen of Monro? a)  Connects the 4th ventricle with the

subarachnoid space

b)  Connects the right lateral ventricle with the left lateral ventricle c)  Connects each of the lateral ventri-

cles with the 3rd ventricle d)  Connects the3rdand 4thventricles e)  It is located at the atrium

5.Which of the following better describes the 3rd cranial nerve?

a)  It crosses between the PCA and SCA b)  It has sympathetic fibers coming from the Edinger-Westphal nucleus­

c)  It reaches the orbit through the op- tic canal

d)  It arises from the pontomedullary sulcus

6.Please select the correct statement regarding the pterion:

a)  Suture between the frontal-zygo- matic-temporal-sphenoid bones b)  Suture between the frontal-sphe- noid-temporal-parietal bones c)  Suture between the frontal-zygo- matic-parietal-sphenoid bone d)  Suture between the frontal-zygo- matic-parietal-temporal bones

7.The ambient cistern is located at the level of:

a)  Anterior midbrain b)  Anterolateral midbrain c)  Posterolateral midbrain d)  Posterior midbrain e)  None of the above

8.The ophthalmic artery most commonly arises from:

a)  ACoA b) A1

c) C6

d) Clinoid segment of the ICA e) Common ophthalmic artery

9.The body of the α-motor neurons are most commonly located in which of the followings:

a) Dorsal root ganglia b) Rexed lamina IX c) Anterior spinal root d) Rexed lamina II

10.Which of the following statements is true regarding the brainstem?

a)  The only cranial nerve arising from the posterior surface is the 4th cranial nerve

b)  The basilar artery provides blood supply to the entire anterior surface of the brainstem

c)  The CN V exits through the pon- tomedullary sulcus

d)  The superior cerebellar peduncle crosses between the corticospinal tracts in the anterior pons

4.9.2  Answers

1.d. The middle meningeal artery (branch of the internal maxillary artery), enters the skull through the foramen spinosum. The foramen lacerum is occupied by fibrocartilage resulting­ from the confluence of the petrous portion of the temporal bone with the sphenoid and occipital bones. The deep and greater petrosal nerves cross the lacerum. The foramen ovale is occupied by the mandibular nerve (V3) and lesser petrosal nerve. The maxillary nerve (V2) crosses the foramen rotundum.

2.d. The meningohypophyseal trunk arises from the cavernous segment of the ICA. Three main branches from this trunk have been described: Tentorial artery (Bernasconi and Cassinari artery), dorsal meningeal artery, and the inferior hypophyseal artery.

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3.f. Following a craniocaudal order: The body of the upper motor neuron is located at the primary motor cortex, the axons form the corona radiata which travels through the posterior limb of the internal capsule to reach the middle three-fifth of the cerebral peduncle, they continue down to the anterior pons. On the medulla, it forms the pyramids decussating approximately 90% of the fibers in the lower one-third to finally reach the spinal cord where it travels in two different bundles (anterior and lateral corticospinal tract).

4.c. There are two foramen of Monro. Each of them connects the ipsilateral lateral ventricle with the 3rd ventricle. The 4th ventricle drains CSF to the subarachnoid space through one medial foramen (Magendie) and two lateral foramen (Luschka). There are not normal connections between the right and left lateral ventricles. The 3rd and 4th ventricles are connected through the cerebral aqueduct.

5.a. Once the CN III leaves the interpeduncular cistern, it crosses between the PCA (superiorly) and SCA (inferiorly). The Edinger-Westphal nucleus provides parasympathetic fibers. The only CN occupying the optic canal is the optic nerve (CN II). CN III reaches the orbit through the superior orbital fissure. The CNs at the pontomedullary sulcus are (from medial to lateral) CNs VI, VII, and VIII.

6.b. The pterion is the suture between the frontal-sphenoid-temporal-pari- etal bones.

7.c. The ambient cistern is located at the posterolateral midbrain. The interpeduncular cistern is located anterior. The quadrigeminal cistern is located posterior to the midbrain.

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8.c. The most common origin for the ophthalmic artery is the C6 segment of the ICA, also known as ophthalmic segment (from the distal dural ring to the P-Comm). This segment also gives the superior hypophyseal artery.

9.b. The α-motor neuron in the spinal cord are located on Rexed lamina IX. Dorsal root ganglia have the body for the sensory neurons. The anterior spinal root has the motor axons. Rexed lamina II has the substantia gelatinosa for exteroceptive neurons.

10.a. The only CN arising from the posterior surface of the brainstem is the CN IV or trochlear nerve. It is also the only CN which decussates. The BA provides irrigation mostly to the pons. The CN V exits at the anterolateral surface of the pons. The superior cerebellar peduncle crosses at the inferior midbrain.

References

[1]Kempe LG. Operative Neurosurgery: Volume 1 Cranial, Cerebral, and Intracranial Vascular Disease. Springer Science & Business Media; 2013

[2]Adel KA, Ronald AB. Functional Neuroanatomy: Text and Atlas. Functional Neuroanatomy: Text and Atlas. 2005

[3]Sara SJ. The locus coeruleus and noradrenergic modulation of cognition. Nat Rev Neurosci. 2009; 10(3):211–223

[4]Rouviere H, Delmas A. Anatomía humana. Descrip- tiva, topográfica y funcional. 2005;1:336–414

[5]Perlmutter D, Rhoton AL, Jr. Microsurgical anatomy of the distal anterior cerebral artery. J Neurosurg. 1978; 49(2):204–228

[6]Cilliers K, Page BJ. Description of the anterior cerebral artery and its cortical branches: variation in presence, origin, and size. Clin Neurol Neurosurg. 2017; 152:78–83

[7]Rhoton AL, Jr. The supratentorial arteries. Neurosurgery. 2002; 51(4, Suppl):S53–S120

[8]Fernandes-Cabral DT, Kooshkabadi A, Panesar SS, et al. Surgical management of vertex epidural hemat-

oma: technical case report and literature review. World Neurosurg. 2017; 103:475–483.

5.1  Introduction

Timely and accurate performance and interpretation of neuroimaging are essential for the care of the acute neurological patient. While a detailed neurological examination can provide a wealth of specific information about the site of pathology in the neuroaxis, the majority of the central nervous system (CNS) is occult to the human eye, ear, and touch. It is one of the few systems that cannot be visually inspected, auscultated, or palpated noninvasively. As such, most patients with a neurological problem undergo some form of imaging, with the specific imaging test determined by the patient's presentation­ and the acuity of the symptoms. ­Computed tomography (CT), conventional magnetic resonance imaging (MRI), and ultrasound comprise the majority of neuroimaging

studies performed during the course of the typical neurological workup. Advanced imaging modalities such as magnetic resonance (MR) perfusion, MR spectroscopy, and diffusion tensor imaging are reserved for special indications such as brain tumor imaging at specialized centers.

5.2  Computed

Tomography

CT is the workhorse for the acute neurological patient ( Fig. 5.1, Fig. 5.2); it is fast, widely available, and is able to exclude the majority of cranial and spinal emergencies that would require a trip to the operating­ room. Unlike MRI, there are no compatibility issues with CT for clinical monitoring devices in critically ill patients, and no metal

screening is required. In the trauma patient, CT readily shows the presence of blood in the various intracranial compartments. Acute hemorrhage is hyperdense on non-contrast CT in comparison to brain and cerebrospinal fluid (CSF), and is readily detected when present even in small amounts. Other pertinent­ information, such as the presence of midline shift, ventriculomegaly/­ hydrocephalus, herniation, depressed skull fractures, and radiopaque foreign bodies can also be evaluated by CT. In the patient presenting with an acute stroke syndrome, a non-contrast CT can distinguish between hemorrhagic and ischemic strokes, enabling timely administration of intravenous tissue plasminogen activator (tPA) in the absence of other contraindications. It can also help to differentiate conditions that might mimic other neurologic diseases.

In addition to the detection of acute hemorrhage, CT is also excellent for assessing bony pathology and calcification.

Subtle skull fractures, paranasal sinus/ mastoid pathology, and temporal bone disease are better evaluated on CT than on radiographs or MRI.

5.3  Magnetic Resonance

MRI provides exquisite soft tissue contrast and detail of the intracranial ( Fig. 5.3, Fig. 5.4, Fig. 5.5) and intraspinal ­structures, and is therefore the imaging test of choice whenever direct parenchymal assessment of the brain, orbits, skull base, cranial nerves, or spinal cord is required. Proper interpretation of an MRI study requires familiarity with the various sequences, the information they provide, and their pitfalls/­ associated artifacts. Some standard MR sequences include T1-weighted images (T1WI),T2-weightedimages(T2WI),fluid- attenuated inversion recovery (FLAIR), gradient-recalled echo (GRE), diffusion weighted imaging (DWI), and post-­contrast T1-weighted images.

An important caveat is that MRI is not adequate for the detection of fractures, therefore, MRI may be used to supplement but not replace CT in the setting of trauma.

5.3.1  MRI Sequences

T1WI are good for evaluating anatomy. Fat, blood, and proteinaceous products can appear whiter in signal on T1WI.1 Application of fat-suppression on T1WI can distinguish between fat and blood in

cases of a T1 hyperintense mass.2 T2WI highlight many pathologic processes in the brain that produce either edema or areas of signal abnormality which tend to be lighter in signal intensity on T2WI. FLAIR images are also T2WI, but with suppression of signal from bulk water such as CSF in the subarachnoid space. This allows T2-bright pathologic processes in the brain or CSF space to be more conspicuous and easier to detect. GRE images are sensitive for the detection of subacute or chronic blood products in the brain because of their magnetic properties yielding a dark, low, or hypointense signal. Hypointensity on GRE is not specific for blood products however, and other substances like calcium or metal can also appear hypointense to varying degrees. DWI is the most sensitive and specific MR

technique for the diagnosis of acute cerebral infarction.3 Areas of acute infarction will appear bright on the DWI sequence and dark on the corresponding apparent diffusion coefficient maps.3 Post-contrast imaging increases the sensitivity of MRI for detecting pathologic changes in the brain. Areas of subtle T1 or T2 signal abnormality sometimes show striking enhancement on the post-contrast images, increasing the likelihood that they will be detected. Contrast enhancement can also distinguish between truly cystic/nonenhancing lesions and cyst-like brain masses which will enhance along their periphery. In general, most patients with suspected intracranial infection or tumor who undergo MRI should also have contrast­ -enhanced imaging, as this helps with detection and characterization of intracranial abnormalities.

5.4  Clinical Scenarios

5.4.1  Epidural Hematoma

Imaging of epidural hematomas is primarily done with CT, as these patients may be unstable or under consideration for emergent decompression. The classic appearance of an acute epidural hematoma is a lentiform or convex hyperdense extra-­axial (external to the brain) mass that does not cross the lambdoid or coronal suture lines ( Fig. 5.6). However, epidural hematomas can cross the midline sagittal suture as the periosteal layer of the calvarium forms the outer layer of the dura, and extravasated blood would be external or “epi”-dural to this layer. Epidural hematomas can cross

the tentorial leaflets for a similar reason. The hematoma usually causes mass effect on the underlying brain, and there may be midline shift to the contralateral side. The hematoma usually happens on the same side as the soft tissue swelling (i.e., the site of the traumatic blow), and there is usually an underlying skull fracture which leads to laceration of the middle meningeal artery. In some instances, epidural hematomas may also be venous in origin, particularly in the posterior fossa.4

5.4.2  Subdural Hematoma

Subdural hematomas are located in the potential space between the dura mater and the pia-arachnoid mater. In older

patients, these collections may occur after minimal trauma as a result of brain atrophy and stretching of the cortical bridging veins, which makes them vulnerable to injury. In younger patients, these collections occur after substantial trauma, and are usually located opposite to the side of traumatic head impact. On CT, subdural hematomas typically appear as hyperdense crescentic collections that cross suture lines. In the region of the vertex or falx cerebri, subdural hematomas layer along the falx and tentorial leaflets without­ crossing these structures. One important pitfall on CT to be aware of are older hematomas that have degraded and therefore may appear of similar density to the adjacent brain (i.e., an isodense subdural collection), and may be difficult to detect without a high index of suspicion ( Fig. 5.7). In the absence of significant midline shift, abnormal thickening or blurring of the gray matter on the side of the isodense subdural hematoma may be the only finding­ on CT.

Equivocal cases of suspected isodense or thin subdural hematomas can be confirmed on MRI, which can show extremely thin collections on FLAIR images.

5.4.3  Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) has a distinctive appearance on CT, with hyperdensity conforming to the cisterns and sulci of the brain ( Fig. 5.8). The most common cause of SAH is trauma, which usually presents with scattered areas of sulcal hyperdensity on CT. This is in contradistinction to aneurysmal SAH, which usually presents with large or diffuse dissemination of hyperdense material in the sulci and cisterns at the base of the brain ( Fig. 5.8).

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Fig. 5.7  Isodense left subdural hematoma. A 69-year-old female presents with chronic headache. Axial nonenhanced CT scan shows concave-shaped isodense blood products along the left hemispheric convexity. The hematoma crosses suture lines indicating that it is within the subdural space. There is mild mass effect on the underlying parenchyma but no midline shift. These findings are compatible with subacute subdural hematoma. (Image is provided courtesy of Thomas Jefferson University Hospital.)

The location of the greatest amount of SAH can be a clue to the location of the ruptured aneurysm; focal clot in the anterior interhemispheric fissure is classic for a ruptured anterior communicating aneurysm, or a focal clot or large SAH in the Sylvian cistern is suggestive of a ruptured middle cerebral artery (MCA) aneurysm.5 A pertinent finding to include in every imaging evaluation of aneurysmal SAH is the presence or absence of hydrocephalus. Ventricular dilatation, particularly of the temporal horn, is a key imaging feature of acute hydrocephalus on CT.6

Abnormally low signal may be seen around the ventricles in cases of acute hydrocephalus, which represents transependymal CSF flow or flow that is impeded from the normal resorption pathway at the convexity.

On MRI, SAH can be seen as abnormally bright signal in the CSF spaces on FLAIR imaging. Hypointense material in the sulci may also be seen on the GRE sequence.

5.4.4  Parenchymal Hemorrhage

Hypertension is the most common cause of nontraumatic parenchymal hematoma in older patients. In nonhypertensive elderly patients, cerebral amyloid angiopathy is a leading cause. Hemorrhagic conversion of a recent infarct or hemorrhage into an existing neoplasm should also be considered in older patients. An intraparenchymal hematoma in a young adult raises a different specter of diseases, with other etiologies like an underlying vascular malformation or

illicit drug use being among the leading considerations.7

Acute parenchymal hematomas appear as hyperdense space-occupying masses on CT. If hemorrhage occurs close to the ventricular surface, the hematoma may dissect into the ventricle with secondary intraventricular hemorrhage and possibly hydrocephalus. The volume of parenchymal hematoma has been correlated with risk of morbidity and mortality.8 Other important imaging findings to note (or to ask the radiologist about) are the ­presence and degree of midline shift, and evidence of herniation (manifested as effacement/obliteration of the CSF spaces surrounding the brain). As acute hematomas evolve, the degree of surrounding edema increases, peaks, and then gradually subsides. The hematoma eventually fades and disappears from the outside in, reminiscent of a melting ice cube.

5.4.5  Cerebral Edema

Diffuse cerebral edema can be seen after trauma or prolonged anoxia, and findings on CT can be subtle when imaging is performed early in the disease course. Typical CT findings include loss of gray-white differentiation, effacement of the basal cisterns and cortical sulci (due to cerebral swelling), and increased attenuation of the falx, tentorium, and subarachnoid spaces.

“dense cerebellum” sign).10 CT findings in early cerebral edema can be easily missed, particularly in young patients without much atrophy. However, the basal cisterns should always be visible on head CT in every patient.

5.4.6  Ischemic Stroke

CT is insensitive for early acute infarction. The main role of CT is to exclude intracranial hemorrhage or large areas of completed infarction prior to intravenous tPA infusion.

Imaging findings in early acute ischemic stroke are subtle, but include loss of graywhite differentiation, blurring/indistinctness of the basal ganglia, loss of the insular cortex, and a hyperdense vessel (from thrombus).11

MRI is much more sensitive for the detection of acute stroke, and shows restricted diffusion conforming to the territory of the occluded artery ( Fig. 5.9, Fig. 5.10,Fig. 5.11, Fig. 5.12, Fig. 5.13 ).3 MRI can also be used to detect subtle hemorrhagic conversion of acute ischemic stroke, which would be best visualized on the GRE sequences.

The increased attenuation of the CSF spaces in diffuse cerebral edema is multifac­ torial,butcanbemistakenforSAH(so-called

“pseudo-subarachnoid” pattern).9

There may also be relatively low attenuation of the cerebral hemispheres compared with the cerebellum, causing the cerebellum to appear artifactually dense (so called

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5.4.7  Aneurysms

Familiarity with imaging, treatment, and surveillance of intracranial aneurysms is an important part of any neurosurgical practice. In general, the two main noninvasive methods for diagnosing intracranial aneurysms are CT or MR angiography. CT has several advantages over MRI in the acute setting. In addition to being more widely available and quicker to perform,