Ординатура / Офтальмология / Английские материалы / Neuro-Ophthalmology_Kidd, Newman, Biousse_2008

do not express a hormone excess, and the patient is often either partially or completely panhypopituitary.

The classic visual presentation is of a bitemporal field loss, which is often not symmetrical. Early compression leads to upper temporal field desaturation for red, and the mass may compress one side of the chiasm earlier than the other. The position of the optic nerves and chiasm in relation to the sella is variable and about 12% of the population has a pre-fixed chiasm and a lesser proportion post-fixed. Pre-fixed chiasmata present with optic tract signs, which is typical of some rarer parasellar pathology, particularly craniopharyngiomas. Lesions that affect the intracranial optic nerves obviously affect one eye alone. These may be lesions of the optic nerve itself, its sheath, or adjacent structures, typically adenomas with a post-fixed chiasm or planum or anterior clinoid meningiomas. It is worth noting that for compressive lesions, it is the field that is damaged first, and acuity loss occurs as a later event.

Investigating the visual fields is in principle easy; confrontation with a red pin is fast, easy, and accurate. It is often skipped in busy clinics, particularly if other more common eye pathology is being investigated; pituitary patients who have been investigated in glaucoma and other clinics for a while before the diagnostic “penny dropping” are not unheard of, even in famous postgraduate institutions.

Field testing is now more commonly carried out using Humphrey static perimetry. This is accurate and repeatable wherever the test is carried out but does require a permissive level of vision for accurate testing. In the severely damaged eye, the Goldmann kinetic perimeter carried out by an expert remains the most accurate assessment. This is also true when other ophthalmic pathology coexists.

Visual acuity is usually preserved until late in the disease process. Its testing with the Snellen chart may give an impression of accuracy—records in the notes such as “6/24 left and 6/9 right” seem so precise—but lighting levels and distance from the chart are usually poorly understood by those using them, hence their accuracy should not be relied on, particularly in some surgical series.

Parasellar pathology, which involves the cavernous sinus, commonly presents with ophthalmoplegia. Pituitary apoplexy, particularly, may present with a third nerve palsy rather than chiasmal compression, as does a cavernous sinus meningioma. Many other less common lesions also present in this fashion (Table 10–1). Fourth and sixth nerve palsies may also be the only physical sign.

HEADACHE AND SYMPTOMS OF RAISED INTRACRANIAL PRESSURE

Headache is present at the diagnosis in 33% to 50% of most series of pituitary adenoma and is not uncommonly the only presenting symptom. However, because headache has in recent years become a symptom justifying a scan, the tumor may present earlier than it otherwise may have done. Why pituitary tumors cause headache appears unknown. Even a large pituitary tumor seldom causes true raised intracranial pressure in the same way as a malignant process or a large meningioma. However, stretching of the basal dura must occur and in particular distortion of the medial wall or position of the carotid in the cavernous sinus may be responsible. This was a frequent enough occurrence as to be used a diagnostic tool in carotid angiography for pituitary adenomas in the pre-computed tomography (CT) era.

clinician is to decide what to do about them. Modern pituitary surgery is safe and effective, but there is nothing so depressing for a surgeon than to cause hypopituitarism or, worse, visual defects in a patient who had previously had no complaints. Although these complications are fortunately rare, the mantra of “if it works, don’t fix it” is one that the judicious surgeon should follow. If the patient has no complaints, surgery can only make him or her worse. Clearly, if vision is borderline normal or pituitary function is all at the bottom end of the normal range, a more interventional view can be taken. It is perfectly acceptable to monitor the patient for a time without treatment, with neuro-ophthalmic examinations, pituitary function, and magnetic resonance imaging (MRI) at twice yearly intervals.

Tumor Types

PITUITARY ADENOMAS

The list of potential lesions in the fossa and parasella area is long. As mentioned previously, adenomas are much the most common, followed by meningiomas, Rathke’s cleft cyst, and craniopharyngiomas. These are discussed in some detail, the remaining lesions less so.

Tumors may be small—microadenomas (Fig. 10–2) are defined as less than 1 cm, but in Cushing’s disease, adenomas may be even smaller, 3 mm is the limit of the best magnetic resonance (MR) images. Tumors greater than 1 cm but constrained within the sella are described by many as mesoadenomas (Fig. 10–3). Macroadenomas are more than 1 cm and are those that typically affect vision. They can be further defined by shape and size. Huge multilobed tumors exist as well but are still termed macroademonas (Fig. 10–4).2

In postmortem studies, silent pituitary lesions are surprisingly common. Tumors arise from cell lines within the anterior lobe of the gland. It is simplistic to think only in terms of nonfunctioning and functioning adenomas, the latter group consisting of prolactinomas, somatotroph (GH-secreting) tumors, Cushing’s (ACTH-secreting) tumors, and the rare TSH-secreting tumor. Many

Figure 10–2 Coronal magnetic resonance imaging, T1 with enhancement. Typical microadenoma (growth hormone secreting).

(>75% response). Of the remainder, GH-secreting tumors do shrink, although seldom to any significant degree, with somatostatin analogues although GH production can be halted. A proportion also responds to cabergoline. Pretreatment of Cushing’s tumors by blocking the adrenal output of cortisol is sometimes offered using either metyrapone or ketoconazole.

Surgery is carried out using the transsphenoidal route in the majority of cases. It is a very effective method for decompressing the chiasm and most surgical series report an improvement of more than 80% in visual fields with a reasonable proportion returning to normal. For hormone-secreting tumors, the results of surgery depend on both the size and shape of the tumor and the experience of the surgeon. For GH-secreting tumors, control is reported to be between 65% to 80þ%. For Cushing’s tumors, in which about one third do not have an MRIvisible tumor, the result is between 65% overall and more than 80% when a microadenoma is seen on MRI. Microprolactinomas are seldom operated on; however, when surgery is carried out by experts, control is achieved in more than 80%.

Craniotomy is reserved for the giant tumors that have multiple lobes. The tumors also shrink well, if slowly, with radiotherapy. Safe regimens were devised long before surgery became safe. Modern techniques such as stereotactic conformal linear accelerators and gamma knife have further refined the results. Radiotherapy is mainly used for recurrences and for hormone-secreting tumors following failed surgery.

Pituitary carcinomas are fortunately extremely rare. They often arise from ACTH-staining types (Fig. 10–5), with a long latent history, and patients may have had radiotherapy in the past. They seldom respond well either to radiotherapy or to surgery, although there is no other therapy except in the even rarer type that transform into a sarcoma.

MENINGIOMAS

These common intracranial tumors occur anywhere within the skull dural lining but arise often in the sella area.59–63 More common in women by a ratio of 3:2,

they are derived from the arachnoid villi and are usually benign. The World Health Organization grades them into three subtypes: I (benign, the vast majority), II (atypical), and III (carcinomatous). The majority, particularly in the sella area, are type I. Four sites require consideration:

Figure 10–5 Coronal magnetic resonance imaging, T1 with enhancement. Malignant transformation of Cushing’s tumor invading the cavernous sinus.

246Neuro-Ophthalmology: Blue Books of Neurology

1.On the planum sphenoidale, they present with chiasmal compression (Fig. 10–6) but virtually never with pituitary hormone involvement. Slightly more lateral, but within the area, those arising from the clinoid are less frequent.

2.More extensive tumors of the sphenoid wing can also be considered in this group, although they only infrequently involve visual pathways. The hyperostotic type (Fig. 10–7) causes bony thickening leading to proptosis and ultimately reduction of the optic nerve canal.

3.Cavernous sinus and sinus-involving petroclival meningiomas may have extensive slow creeping spread by the time they present, usually with ophthalmoplegia (Fig. 10–8), although occasionally with the effects of hyperprolactinemia.

Figure 10–6 Sagittal magnetic resonance imaging, T1 with enhancement. Large planum meningioma lifting and compressing optic nerves and anterior cerebral arteries.

Figure 10–7 A, Computed tomography of hyperostotic left sphenoid wing meningioma with small intraorbital component presenting as disfiguring proptosis and early visual loss. The optic nerve canal is just starting to be involved. B, Axial magnetic resonance imaging, T1 with enhancement. Long-term results of partial resection of a similar tumor involving the left sphenoid wing twelve years previously, without progression.

Figure 10–8 Coronal magnetic resonance imaging, T1 with enhancement, of a cavernous meningioma presenting with severe trigeminal pain and ophthalmoplegia during pregnancy.

Figure 10–9 A, Axial magnetic resonance imaging (MRI), T1 with enhancement, of optic nerve sheath meningioma. The patient presented with rapid unilateral loss of vision. B, Coronal MRI, T1 with enhancement. The same tumor, just starting to erupt into cranial compartment on planum.

4.Optic nerve sheath meningiomas involve the orbit but sometimes extend cranially onto the planum to involve the other eye (Fig. 10–9). These tumors present with monocular progressive visual loss. The loss is painless as the tumor volume is small. These are discussed further in Chapter 9.

Treatment

Although these tumors are in essence challenges for surgical technique, they do respond to radiotherapy, and many modern experts advocate limited decompressive surgery, followed by irradiation for the inaccessible parts. Surgery is usually carried out by craniotomy although endoscopy surgeons are now recommending

solid craniopharyngioma compressing the grossly edematous chiasm from behind. The tumor projects into the third ventricle. Note the normal gland below. This patient presented with behavioral problems and severe visual loss.

CRANIOPHARYNGIOMAS

Sharing their origin with the Rathke’s cleft cyst, craniopharyngiomas have a much less benign course despite their ostensibly benign nature (Fig. 10–11). The age of presentation is biphasic; it is one of the commonest supratentorial tumors in childhood, with a second peak in late adult life. In children, they often present with hydrocephalus, but otherwise present like the Rathke’s cleft cyst.

There are two different types: the commonest, the adamantinomatous, which contains cysts of dark shimmering green “engine oil” appearance as well as solid clumps of almost caseous material, and the less common papillary, in which the lesion is predominately a simple cyst. This type has a better prognosis. It has been suggested that it is a variant of the Rathke’s cleft cyst, but it has a distinct difference in histologic terms; all contain stratified squamous epithelial elements with calcification and cholesterol clefts.

Only 20% lie within the sella, many existing in and around the third ventricle and suprachiasmatic cistern. Some have their origin within the sphenoid and a few outside this defined line of the Rathke’s pouch.

Treatment

Their management is controversial.79–95 Hydrocephalus is managed with shunts and carries a worse prognosis in children. Surgical series are full of “cures” from radical excision, but because many of these tumors involve vital structures such as the hypothalamus and optic nerves to which they are closely applied, complete separation is technically challenging and surgeons can easily be deluded into thinking they have achieved a total excision. Recurrences are common, although subtotal excision may lead to long remission. Furthermore, surgical damage, particularly to the hypothalamus, can wreck the patient whose subsequent life can be marred by hyperphagia, poikilothermia, and other hypothalamic problems.

Most management regimens therefore concentrate on surgical excision of easily removable parts followed by radiotherapy. Many surgeons use cyst catheters to control volume expansion, particularly while radiotherapy controls the remnant tissue. Most patients need long-term endocrine, surgical, and neuroophthalmologic care because late recurrences can be seen.