Fig. 1.1
Blood supply to the pituitary gland. Note that most of the blood supply to the anterior pituitary is provided by the portal vessels, but the blood supply to the adenomas by the inferior hypophyseal artery. 1 Anterior lobe of the pituitary gland (adenohypophysis), 2 posterior lobe of the pituitary gland (neurohypophysis), 3 infundibular stalk, 4 superior hypophyseal artery, 5 inferior hypophyseal artery, 6 primary plexus of hypophyseal portal system, 7 secondary plexus of hypophyseal portal system, 8 capillary plexus of infundibular process, 9 external plexus, 10 efferent hypophyseal vein to cavernous sinus, 11 hypophyseal portal vein
Pathophysiologically, the mechanism of pituitary apoplexy still remains both a poorly understood and potentially fatal condition (Onesti et al. 1990; McFadzean et al. 1991; Sibal et al. 2004; Semple et al. 2005). In contrast to the normal pituitary gland, the direct arterial source from hypophyseal arteries, rather than portal system, is dominant in pituitary adenomas (Baker 1972; Gorczyca and Hardy 1988). Importantly, it has been reported that the bleeding tendency of pituitary adenoma is five times compared to that of any other brain tumour owing to the unique rich vascular structure of the gland (Wakai et al. 1981). Moreover, the size of the adenoma is a critical factor for the development of pituitary apoplexy, with macroadenomas being at a much higher risk than microadenomas, but the exact cause for this predisposition is unknown (Mohanty et al. 1977; Jeffcoate and Birch 1986; Bills et al. 1993; Arafah et al. 1997; Verrees et al. 2004).
There are various theories upon the pathophysiology of pituitary apoplexy in the current literature. Rovit and Fein (1972) hypothesized that a tumour growing inside the narrow space situated between the pituitary stalk and diaphragm sellae results in compression and distortion of the hypophyseal stalk and the thin vascular network at the diaphragmatic notch, leading to ischaemia and subsequent necrosis of the anterior lobe of the pituitary gland (pars distalis) and the adenoma. Based on the results of angiographic studies, however, some authors oppose with this hypothesis because the blood supply of pituitary adenomas comes from the inferior hypophyseal artery, not the superior hypophyseal artery and its branches, which does not get compressed against the diaphragm sellae (Baker 1972; Cardosa and Peterson 1984; Gorczyca and Hardy 1988). Another theory is the presence of a relationship between the aggressive tumoural behaviour as an ‘intrinsic’ factor leading to haemorrhage (Fraioli et al. 1990).
The pathophysiological mechanisms of the clinical manifestations in patients with pituitary apoplexy are as follows:
1.
An increase in the intrasellar contents during the pituitary apoplexy causes an increase in intrasellar pressure, resulting in compression of the following: (a) the normal pituitary tissue and its vascular blood supply and various clinical findings including hypopituitarism; (b) adjacent neurovascular structures including internal carotid artery and the third, fourth, fifth and sixth cranial nerves laterally; (c) the optic apparatus superiorly, leading to decreased visual acuity, visual field deficit and/or blindness; and (d) the hypothalamus and brain stem, causing to diminished level of consciousness (Arafah et al. 2000; Verrees et al. 2004; Nawar et al. 2008).
2.
An increase in intrasellar pressure inferiorly may result in leakage of cerebrospinal fluid called rhinorrhoea (Nawar et al. 2008).
3.
Leakage of blood from the intrasellar compartment to the subarachnoid space may cause the signs and symptoms of vasospasm and meningeal irritation (e.g. headache, nuchal rigidity, fever and alterations of consciousness) (Nawar et al. 2008).
Some risk factors such as increased intracranial pressure, arterial hypertension, diabetes mellitus, cardiac surgery, radiation therapy, pregnancy, oestrogen or bromocriptine therapy, dynamic testing of the pituitary, coagulopathies or head trauma should be considered in the pathogenesis of pituitary apoplexy, although it can occur without any precipitating factor in most cases (Mohr and Hardy 1982; Onesti et al. 1990; Semple et al. 2005; Mou et al. 2009; Rajasekaran et al. 2011). In a recent study, Moller-Goede et al. (2011) compared the frequencies of potential risk factors between the patients with pituitary apoplexy and the control group of matched patients with pituitary adenomas. They found that sex, age, tumour size and tumour type revealed no significant difference between patients with pituitary apoplexy and the control group (Moller-Goede et al. 2011). According to results of their study, risk for pituitary apoplexy was significantly elevated in patients with antithrombotic drugs (vitamin K antagonist or platelet inhibitors), but not in patients with cardiovascular risk factors such as diabetes mellitus and arterial hypertension (Moller-Goede et al. 2011).
Conclusion
Pituitary apoplexy is an uncommon but potentially life-threatening complication due to acute infarction or haemorrhage in the pituitary gland. Pathophysiology of pituitary apoplexy, extrinsic compression of arterial supply or intrinsic tumoural factors, is controversial. Patients who may present with headache, visual defect and altered sensorium may be confused with subarachnoid haemorrhage or meningitis. Imaging studies such as CT or MRI play an important role in the diagnosis of pituitary apoplexy. Prompt institution of intravenous fluid and hydrocortisone must be started in patients with haemodynamic instability. Recent studies favour conservative management except for those with increasing neurological deficit and visual defect. Although the treatment of pituitary apoplexy is still a matter of debate with regard to surgery, the results of early transsphenoidal procedure within 1 week after pituitary apoplexy are satisfactory than patients operated later. Outcome is similar with either conservative management or surgery in more recent studies. Ideally, patients with pituitary apoplexy should be treated through a multidisciplinary team including neurosurgeons, endocrinologists, neuro-ophthalmologists, neuroradiologists, neurologists and radiation oncologists.
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