Tuber cinereum proximity to critical major arteries: a morphometric imaging analysis relevant to endoscopic third ventriculostomy.

BACKGROUND: Arterial bleeding in the interpeduncular fossa is a dreaded complication of endoscopic third ventriculostomy (ETV). When the "safe zone" of the tuber cinereum (TC) is fenestrated, the basilar artery tip (BT) or its branches may be encountered below the third ventriclular floor. Major arterial injuries might be avoided by careful preoperative planning. We aimed to establish previously unavailable normal magnetic resonance imaging (MRI) and MR angiographic (MRA) morphometry and configuration of the BT and posterior cerebral artery P1 segments relative to the TC. METHODS: We analyzed images of 82 patients with non-dilated ventricles (mean Evans' index 0.26), and lying in a neutral head position (mean cervico-medullary angle 141°). We cross-referenced axial MRAs with sagittal MRIs to measure distances of BT and P1 segments from the TC, and to classify the location of the BT in the interpeduncular and suprasellar cisterns. We correlated the sagittal areas of these cisterns and patients' ages with the TC-to-artery distances using regression analysis. RESULTS: The BT, right P1 and left P1 segments were a mean 4.9 mm, 5.5 mm, and 5.7 mm respectively from the TC. Seventy-four percent of BTs were anterior to the mammillary bodies. These distances and locations did not correlate with age (mean 53 years) or size of basal cisterns. CONCLUSIONS: The normal BT and P1 segments are anatomically close to the TC and potentially at risk during ETV in adults of all ages. The new morphometric data presented, along with cross-referencing of preoperative multiplanar images, could help reduce vascular complications during ETV.

Mechanism of tuberothalamic infarction.

BACKGROUND AND PURPOSE: The tuberothalamic artery (TTA), one of the arteries supplying the paramedian thalamic area, is peculiar because it originates from the posterior communicating artery (p-comA), which connects the vertebrobasilar and carotid systems. METHODS: From Stroke Registry, 23 consecutive patients with an acute infarction involving the TTA were selected. We investigated the mechanism of TTA infarction. RESULTS: Fourteen of 23 patients (61%) had coexisting infarctions outside the TTA territory (carotid in three, vertebrobasilar in seven, and both carotid and vertebrobasilar arteries in four patients). Coexisting lesions were most common in the posterior thalamoperforating arterial territory (seven patients). Eleven out of 14 patients (79%) with coexisting lesions had embolic sources from the heart or proximal atherosclerotic arteries, and cardioembolism was the most common mechanism. However, eight of the nine patients with isolated tuberothalamic lesions were classified as small vessel occlusions. More patients with embolic sources had visible p-comA or fetal-type posterior cerebral arteries. The vertebrobasilar arterial system played a more dominant role in developing tuberothalamic infarction than the carotid arterial system. CONCLUSIONS: Isolated TTA infarctions are rare and mostly because of small vessel occlusion. Patients with coexisting infarctions outside TTA territory usually have an embolic source, predominantly vertebral artery atherosclerosis.

Morphology and function of capillary networks in subregions of the rat tuber cinereum.

The differentiated cytology, cytochemistry, and functions within subdivisions of the tuber cinereum prompted this morphometric and physiological investigation of capillaries in the medium eminence and arcuate nucleus of albino rats. Morphometric studies established that the external zone of the median eminence had 3-5 times the number and surface area of true and sinusoidal capillaries than the internal or subependymal median eminence zones, or either of two subdivisions examined in the arcuate nucleus. Type-I true capillaries, around which Virchow-Robin spaces comprise 1% of arcuate tissue area, were situated proximally to the median eminence border. This finding is consistent with a premise that confluent pericapillary spaces enable infiltration of arcuate neurons by factors from capillary blood from the median eminence or Virchow-Robin spaces. Physiologically, the rate of penetration across the median eminence capillaries by blood-borne [14C]alpha-amino-isobutyric acid (a neutral amino acid used as a capillary permeability tracer) was 142 times greater than for capillaries in the distal arcuate nucleus within 12 s of tracer administration. A new finding was that the proximal arcuate nucleus had a permeability x surface area product of 69 microliters g-1 min-1, 34 times greater than that in more distal aspects of the tuber where blood-brain barrier properties exist. We also found that the microcirculatory transit time of a plasma space marker, [14C]sucrose, was considerably longer (1.2 s) in the median eminence and proximal arcuate nucleus than in the distal arcuate or ventromedial nucleus (0.4 s). By virtue of its high capillary permeability and extensive blood-tissue surface area, including the wide Virchow-Robin spaces, the median eminence external zone could be a gateway for flooding other tuberal compartments with blood-borne factors. This effect may be compounded by capillary bed specializations in the proximal arcuate nucleus where Type-I true capillaries, Type-III sinusoids, and pericapillary spaces are confluent with those in the median eminence. The results indicate that the proximal arcuate parenchyma could be exposed to circulating neuroactive substances on a moment-to-moment basis.