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

Intracranial Pathology of the Visual Pathway

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Fig. 7.18a,b. A 25-year-old woman with progressive visual deficit. Diagnosis: macroadenoma of the pituitary gland. T1weighted MRI: a Coronal native view with distinct differentiation of the structure of the superiorly depressed chiasm (arrowheads) from the impressing macroadenoma. The indentation of the tumor is due to the remnant of the sellar diaphragm. b Corresponding, contrast-enhanced image demonstrating inhomogeneous enhancement of the tumor; the cres- cent-shaped signal enhancement corresponds to the cranially displaced and impressed remnant of the pituitary gland with normal enhancement.While the chiasm is less clearly differentiated than in a, the cranial nerves are visualized in the cavernous sinus (arrowhead pointing N III). (From Müller-Forell and Lieb 1995)

homogeneous signal enhancement after contrast (Figs. 7.15, 7.18, 7.20). This applies in particular to medium-sized adenomas, while signal homogeneity in macroadenoma alters in relation to the number of regressive changes. These include cysts (Fig. 7.21), hemorrhages (Figs. 7.12, 7.13), and calcification, requiring not only T1-weighted but also T2-weighted and T2*weighted sequences.The differential diagnosis from other suprasellar lesions as, e.g., craniopharyngioma or cysts of Rathke’s pouch may be difficult in purely cystic macroadenoma. Therapy with bromocriptine in prolactinoma is known to cause intratumoral hemorrhages that are frequently not identified clinically. In contrast to intracavernous meningiomas, the invasion of the cavernous sinus by macroadenomas normally does not lead to narrowing of the ICA,equivalent to a relatively slight impairment of cranial nerves III–VI. Sagittal images provide a superior demonstration of a subfrontal, retrosellar, or hypothalamic extension and/or compression of the third ventricle. The so-called invasive adenoma is a biologically benign, but aggressively growing lesion, capable of destroying the skull base with invasion of the bony sphenoid sinus and infiltration of the cavernous sinus. Primary sellar destruction caused by the very rare pituitary carcinoma may additionally lead to intracranial or intraspinal CSF metastasis (Sartor 1992; Engelbach et al. 1999).

The differential diagnosis of pituitary adenoma includes meningioma of the sellar region (see chapter 7.2.1.3), craniopharyngioma (see chapter 7.2.1.4), optic gliomas (see chapter 7.2.1.1), germ cell tumors (see chapter 7.2.1.7.1),terato-tumors,chordomas (see chapter 7.2.1.7.4), and even metastasis (Fig. 7.1).

7.2.1.2.2

Inflammatory Lesions, e.g., Pituitary Abscess

Infections of the pituitary gland are highly uncommon and usually become clinically manifest once an abscess has formed (Kucharczyk et al. 1996). The rare entity of pituitary abscesses, mostly caused by gram-positive cocci, is known to occur in the presence of other sellar masses or by contiguous spread from an infected sphenoid or cavernous sinus (Daningue and Wilson 1977; Kucharczyk et al. 1996). The clinical presentation with headache and visual loss is similar to that of other large intrasellar masses; septic fever is reported to be uncommon (Kucharczyk et al. 1996). The diagnosis should be based on the imaging presentation following i.v. contrast administration, showing rim enhancement around a hypointense center, representing the necrosis of the intrasellar tumor, and additional inflammatory infiltration of neighboring sinus and intracranial structures (Fig. 7.11).

7.2.1.2.3

Pituitary Stalk Lesions (Langerhans Cell Histiocytosis)

As already considered in chapter 6.3.1.4.3,Langerhans cell histiocytosis (LCH) may occur as a multifocal systemic or single system disease (Howarth et al. 1999). In 25% of the patients with LCH, the classical clinical triad of Hand-Schüller-Christian syndrome develops, presenting with diabetes insipidus, exophthalmos, and bone lesions (Kucharczyk et al. 1996). As CNS involvement is not uncommon as a part of the systemic process, it is mainly seen in children and characterized by a proliferation of histiocytes (Kepes and Kepes 1969; Tien et al. 1990). The pituitary stalk, as the main target of CNS involvement demonstrates

a thickening, with or without an associated hypothalamic mass, that show an intense contrast enhancement after intravenous administration of gadolinium (Fig. 7.22) (Rosenfield et al. 1990; Tien et al. 1990; Maghnie et al. 1992). The differential diagnosis should include germinoma, neurosarcoidosis, tuberculosis,infiltration of adjacent mass lesions such as craniopharyngioma, and metastasis (Tien et al. 1990).

7.2.1.2.4

Skull Base Disorders

Pathologic processes of the skull base like mucoceles or the even rare case of a cholesterol granuloma of the sphenoid sinus should be differentiated from

intrasellar tumors. As unspecific clinical symptoms of headache will rarely indicate further examination, specific visual or diencephalic disturbances should lead to diagnostic imaging. Cholesterol granuloma are expansile cystic lesions, mainly arising in the temporal bone, which contain hemorrhage and cholesterol crystals and are not yet described in the

sphenoid sinus.They present as hyperintense on both T1-weighted and T2-weighted MRI scans (Fig. 7.23) (Osborn and Rauschning 1994), while mucocele, equally sharply demarcated by expanded, remodeled bony structures, demonstrates quite variable signal intensities, depending on the composition of its protein content (Van Tessel et al. 1989).

Intracranial Pathology of the Visual Pathway

7.2.1.3 Meningioma

Meningiomas are WHO grade I–III tumors consisting of neoplastic meningothelial (arachnoidal) cells, occurring predominantly in middle-aged and elderly patients with a marked female bias of approximately 2:1. They constitute up to 26% of primary intracranial tumors and elicit neurologic signs and symptoms by compression of adjacent structures (Louis et al. 2000). Meningiomas associated with hereditary tumor syndrome such as schwannoma (i.e., in patients with NF2) (Woodruff et al.2000) (Fig. 7.24) mainly occur in younger patients. Approximately 20% of meningiomas are located in the sellar region, with 50% arising from midline structures such as

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the sphenoid plane (Fig. 7.25), tuberculum sellae (Figs. 7.26–7.28), diaphragm sellae, or the dura of the cavernous sinus (Fig. 7.29). The remaining 50% consist of sphenoid wing meningiomas (Figs. 7.30, 7.32, 6.108) or meningiomas of the clinoid process (Figs. 7.14, 7.24, 7.31, 7,33, 6.174) (Sartor 1992). The characteristic hyperostosis associated with these tumors is due to their tendency to invade the Haversian canals (Zülch 1986). As a result of their slow, asymptomatic, and in some instances intraosseous growth, en plaque meningiomas of the middle cranial fossa, including parasellar and sphenoid wing meningiomas, may demonstrate substantial extension (Fig. 7.32). Globular meningiomas of the suprasellar or paraclinoid region may produce early ophthalmological symptoms because of optic nerve

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