Ординатура / Офтальмология / Английские материалы / Imaging of Orbital and Visual Pathway Pathology_Muller-Forell_2005

Fig. 7.45a–k. A 10-year-old boy with headache persisting for 6 weeks and double vision for 2 days; bitemporal hemianopia representing the only neurologic deficit. Diagnosis: astrocytoma (WHO II) of the optic tract, state after ventriculoperitoneal shunt. MRI: a Axial T2-weighted view, demonstrating tumor growth from the right chiasm and hypothalamus along the right optic tract to the lateral geniculate nucleus. Note the lack of infiltration of the left optic tract, visualized as a hypointense structure (white arrow). b Axial T2-weighted image at the level of the anterior commissure with distinct definition of the left optic tract on its way to the lateral geniculate nucleus. Note (as in a) compression of the right mesial temporal lobe as well as infiltration of the ipsilateral anterior thalamus (white arrow). c Axial, T1-weighted, contrast-enhanced image, corresponding image to b, showing signal enhancement in the distal part of the tumor as well as in the thalamus. d Midsagittal, T1-weighted, contrast-enhanced image demonstrating infiltration of the entire chiasm, hypothalamus, and the anterior part of the third ventricle (linea terminalis). e Coronal T1-weighted contrast-enhanced view at the level of the chiasm, demonstrating lateralization of the tumor growth. f Coronal T1-weighted view at the level of the optic tract. Note the compression of the right basal vein (arrow). The boy presented for imaging check-up 1.5 years after the initial investigation and additional surgery. Although he did not exhibit new deficits and reported feeling well, an extremely large tumor was visualized. MRI: g Axial T1-weighted native view at the level of the chiasm (compare with a) with distinct infiltration of the chiasm and the mesial temporal lobe, accompanied by a lateral tumor cyst. h Axial, T1-weighted, contrast-enhanced image (compare with b, c) showing the thalamic area of the tumor impinging on the tumor in the optic tract. Note the space-occupying effect with compression of the brainstem (see also g). i Coronal T1-weighted native view (compare with e) demonstrating progressing compression of the chiasm and inferior enlargement to the sellar diaphragm. k Coronal, T1-weighted, contrast-enhanced view at the level of the midbrain (compare with f) showing the entire extension of the recurrent tumor with compression of the temporal horn of the right ventricle (arrow) and an initial midline shift

be assumed in high grade glioblastoma (Figs. 7.8, 7.44) (Russell and Rubinstein 1989; Zülch 1986; Osborn and Rauschning 1994; Atlas 1996).

7.2.1.6 Aneurysms

The classification of intracranial aneurysms can be made morphologically into saccular and nonsaccular aneurysms. Another differentiation is based on a specific etiology as, e.g., congenital degenerative, traumatic, dissecting, infectious, or flow-related aneurysms (in the territory of feeding arteries in cerebral arteriovenous malformations, AVM) (Stehbens 1995; Byrne and Guglielmi 1998). Endothelial dysfunction as the underlying pathological instability has been recognized as the basic pathology (Stehbens 1972, 1995). The actual incidence of intracranial aneurysms is unknown, since published data vary according to the definition of an aneurysm and whether the study is based on autopsy findings, clinical data, or angiographic studies. The estimated incidence rates may thus be too low as a result of incomplete ascertainment caused by the failure to recognize the presence of an aneurysm (Osborn and Rauschning 1994; Byrne and Guglielmi

1998). The rupture of an intracranial aneurysm is the most common atraumatic cause of subarachnoid hemor-rhage (SAH), presenting with a sudden onset of headache, varying loss of consciousness, vomiting, seizure, confusion, and focal neurologic deficits (Fig. 7.46) (Yoshimoto et al. 1979; Adams et al. 1980; Juvela et al.1993).In view of a high incidence of often life-threatening rebleeding (Winn et al. 1977; Kassel and Torner 1983) and/or delayed cerebral vasospasm (Weir et al. 1978; Wilkins 1988), this clinical event requires immediate, either neurosurgical or interventional neuroradiological therapy.

Saccular aneurysms are characterized by non-spe- cific dysfunction of the arterial wall, while in fusiform aneurysms the pathologic lesion may be symmetric or asymmetric, depending on whether the respective arterial wall pathology is serpentine or tubular (Fig. 7.47). Aneurysms occur predominantly in

patients older than 30 to 40 years and are associated with arteriosclerotic degeneration of the arterial wall (Hayes et al. 1967). They are characteristically located at Willis’ circle or its major branches and develop at bifurcations or at the origins of branch arteries (Stehbens 1972, 1995). Some 10%–18% of unruptured aneurysms present with symptoms of mass effect (Figs. 7.47–7.51) (Raps et al. 1993; Khanna et al. 1996). Unruptured symptomatic intracranial aneurysm of the infraclinoid or supraclinoid ICA, the anterior cerebral artery, or (rarely) the basilar artery presents different clinical symptoms, depending on the site of compression of neighboring structures. Orbital, periorbital, or facial pain is the most common symptom of cavernous carotid aneurysms, followed by different types of cranial nerve palsy. Isolated N III palsy may lead to an aneurysm of the posterior communicating artery, while an aneurysm of the ICA is suspected in the presence of a combination of N VI or N IV palsy and a sensory deficit of the trigeminal nerve (Kupersmith 1993a). Neither the extent nor the clinical symptomatology of slowly progressing visual field deficits caused by aneurysms may be readily distinguished from those caused by neoplasms. Depiction of the extent of the visual deficit may fluctuate due to thrombosis and dilation of the aneurysm; in neoplasms, slowly progressive exacerbation, with the exception of hemorrhage or infarction, is typical in pituitary adenoma (Figs. 7.12, 7.13), while cyst expansion might be observed in craniopharyngioma, where acute deterioration of vision may occur (Kupersmith 1993a).

Depending on the origin and the direction of growth, compression of the optic pathway and resulting neuro-ophthalmologic symptoms are variable. Aneurysms of the ICA involving the visual pathway may be classified by their origin,arising from the cavernous (Fig. 7.49), ophthalmic (Figs. 7.46, 7.50), or distal carotid segment (Figs. 7.47, 7.48, 7.51) (Byrne and Guglielmi 1998).

1.Although only 3% of all intracranial aneurysms are found in the cavernous carotid artery segment (Krayenbühl 1973), they comprise approximately 15% of symptomatic unruptured aneu-

rysms (Henderson 1955) and are seen often in women over 40 years of age (Kupersmith 1993a). Because ICA aneurysms of the cavernous segment are located extradurally, subarachnoid or subdural hemorrhage is rare and seen only in intradural extension (Smith et al. 1994); however, pain and progressive unilateral cranial nerve palsy with diplopia, ptosis, blurred vision from accommodative paresis, and anesthesia of the forehead and cornea may lead to diagnostic imaging (Cogan and Mount 1963; Kupersmith et al. 1984). Signs of cavernous sinus dysfunction always precede visual loss due to extension of large aneurysms to the optic canal with optic nerve distortion. In addition, almost all patients have a complete ophthalmoplegia (Fig. 7.49) (Kupersmith 1993a).

2. Carotid ophthalmic aneurysms represent 1.5%–8% of all intracranial aneurysms (Sengupta et al. 1976; Yasargil et al. 1977), but 13% of symptomatic unruptured aneurysms (Locksley 1966). They are defined as intradural aneurysms arising from the ICA just at or above the origin of the ophthalmic artery (C5 or C6 segment), mostly from the superomedial or superior wall, and only rarely from its inferolateral or lateral wall (Drake et al. 1968; Bouthillier et al. 1996; Byrne and Guglielmi 1998; Osborn 1999). The proximity to the intracranial optic nerve is responsible for the most common clinical presentation of ipsilateral acute visual loss, whether in SAH after rupture or in unruptured aneurysms (Figs. 7.46, 7.51). Asymptomatic, even large aneurysms may be clinically tolerated for a long time, and the (sometimes unnoticed) visual loss, generally accompanied by optic nerve atrophy, is caused by chronic pulsatile compression (Fig. 7.50) (Kupersmith et al. 1984; Perneczky et al. 1999). The neuro-oph- thalmological presentation of asymmetric (bilateral) visual deficits is caused by the involvement of the optic chiasm and crossing fiber compression (Ferguson and Drake 1981).

3.Distal internal carotid artery aneurysms are described according to the nearest branch artery. Aneurysms directly involving the visual pathway arise most likely from the superior hypophyseal artery with a clinical presentation similar to that of ophthalmic IAC aneurysms. As aneurysms of the PcoA predominantly cause N III palsy, large or giant aneurysms of the distal ICA at or close to the bifurcation may involve the intracranial optic nerve, the lateral chiasm, or optic tract together or individually. Accordingly, variable neuro-ophthal- mological symptoms and deficits may occur from

ipsilateral scotoma and quadrant-anopia (optic nerve), contralateral temporal quadrantanopia (chiasm), to homonymous hemi-anopia (optic tract).

Patients with aneurysms of the ICA bifurcation (Fig. 7.48), which have an incidence of only approximately 4% of all intracranial aneurysms,often present with headache, hemiparesis, and progressive vision loss as a result of the mass effect. Progressive optic nerve dysfunction with optic atrophy can develop from direct compression or displacement of the optic structures (Ley 1950; Kupersmith 1993a).

Imaging Characteristics. The role of CT and MRI as noninvasive methods is to confirm and define the clinical diagnosis of symptomatic aneurysms following rupture or compression symptoms, while intra-arterial angiography with digital subtraction technique (DSA) remains the preferred technique for cerebral vessels (Byrne and Guglielmi 1998).Without doubt, CT is the method of choice in acute subarachnoid hemorrhage (Fig. 7.46) and demonstrates not only the hemorrhage itself, but also the volume and distribution of the acute hemorrhage and its complication as acute CSF disturbance. As unruptured but symptomatic aneurysms are generally larger than ruptured aneurysms at the time of presentation, secondary changes, e.g., bony erosion of the sphenoid in aneurysms of the cavernous sinus or calcification in the wall (Figs. 7.49, 7.48) can be demonstrated. Partial thrombosis of the lumen may be visible, especially when comparing noncontrast CT images with those after intravenous contrast administration, where the patent portion of the lumen is distinctly hyperdense and the generally highly attenuated clot appears darker (Pinto et al. 1979). Helical scanning by CT-angiography (CTA) (Fig. 7.46) with a relatively high sensitivity for aneurysms larger than 3 mm in diameter during administration of contrast material and secondary 3D-reconstruction is a helpful tool in the acute phase (Schwartz et al. 1994).

MRI is the method of choice in visualizing the vicinity of the aneurysm and its relation to the optic pathway, due to its high sensitivity and spatial resolution, enabling the detection of flowing blood (flow void) and the multiplanar capability. In SE sequences, flowing blood appears dark on both T1and T2-weighted images (Fig. 7.49), while aged blood (methemoglobin) in a thrombus is seen as a signal intense white area, which exhibits an onion-like, mul-

tilayered, laminated shape of the thrombosed part of the clot (Figs. 7.48, 7.50) (Schubiger et al. 1987). On combining the MRI images with 3D TOF or 3D phase contrast MRA (Fig. 7.51), the detection rate of aneurysms greater than 3 mm in diameter is approximately 100% (Ross et al. 1990; Wilcock et al. 1996).

Intra-arterial DSA of the cerebral vessels is still the gold standard in the detection or exclusion of intracranial aneurysms as it represents the most sensitive method available (Figs. 7.46–7.49, 7.51) (Caplan and Wolpert 1991). The method is applied with the aim to determine the anatomical relationship of the lesion, in particular with regard to the size of the

Fig. 7.50. A 58-year-old woman with slowly progressing blurred and double vision persisting for 2 months. Diagnosis: unruptured, partly thrombosed aneurysm of the left ICA. Axial HR-MR: the visualized spherical hyperintensity represents the sack of the aneurysm. In addition to the thrombus [crescent-shaped hypointensity (arrowheads)], the clinical symptoms are due to severe compression of the prechiasmal optic nerve and the chiasm by the aneurysm and aneurysmal pulsation. (From Müller-Forell and Lieb 1995)

ostium and open lumen, the relationship to adjacent arteries, the presence of vasospasm, collateral blood flow, and other vascular pathologies (Osborn 1994c; Byrne and Guglielmi 1998). The protocol includes the transfemoral catheterization of both carotid and vertebral arteries in at least four projections.

7.2.1.7

Miscellaneous (Germ Cell Tumors, Metastasis, Cavernoma of the Cavernous Sinus, Chordoma, Tolosa-Hunt Syndrome, Cystic Lesions)

7.2.1.7.1

Germ Cell Tumors/Pineal Tumors

Germ cell tumors of the CNS constitute an unique class of rare tumors of different malignant character, affecting children and young adolescents. The histopathology and biological behavior of germ cell tumors is similar to homologous germ cell neoplasms arising in the gonads and other extragonadal sites. Even distinctive germ cell tumors are often characterized by overlapping features due to the fact that germinoma as mature teratoma with low mitotic activity (Fig. 7.57) with or without malignant transformation, yolk sac tumor with variable mitotic activity, embryonal carcinoma with high mitotic activity, and choriocarcinoma are included in this group of tumors (Rosenblum et al. 2000). Although germ cell tumors represent only 0.5% of all intracranial neoplasms, approximately 3% are detected in patients younger than 20 years of age. About 80% of CNS-germ cell tumors impinge on the midline with preference for the region of the pineal gland. Other preferred sites include supraor intrasellar locations (Figs. 7.52, 7.53) that are involved simultaneously or sequentially if the tumor is multifocal, but intraventricular (mostly III ventricle), basal ganglionic, and thalamic variants may be encountered (Jennings et al. 1985; Matsutani et al. 1997; Rosenblum et al. 2000). The clinical features of germ cell tumors