Intra- and inter-observer variability in intracranial aneurysm segmentation: comparison between CT angiography (semi-automated segmentation software stroke VCAR) and digital subtraction angiography (3D rotational angiography).

PURPOSE: To compare size and morphologic features of three-dimensional aneurysm models, obtained with a semi-automated segmentation software (Stroke VCAR, GE, USA) from cerebral CT angiography (CTA) data, to three-dimensional aneurysm models obtained with digital subtraction angiography (DSA, with 3D rotational angiography acquisition-3DRA), considered as the reference standard. METHODS: In this retrospective study, we reviewed 132 patients, with a total number of 137 intracranial aneurysm, who underwent CTA and subsequent DSA examination, supplemented with 3DRA. We compared neck length, short axis and long axis measured on 3DRA model to the same variables measured on 3D-CTA model by two blinded readers and to the automatic software dimensions. Therefore, statistics analysis assessed intra-observer and inter-observer variability and differences between patients with or without subarachnoid hemorrhage (SAH). RESULTS: There were no significant differences in short-axis and long-axis measurements between 3D angiographic and 3D-CTA models, while comparison of neck lengths revealed a statistically significant difference, which tended to be greater for smaller neck lengths (partial volume effect and "kissing vessels" artifact). There were significant differences between manual and automatic data measured for the same three variables, and the presence of SAH did not affect aneurysm 3D reconstruction. Inter-observer agreement resulted moderate for neck length and substantial for short axis and long axis. CONCLUSION: The examined 3D-CTA segmentation system is a reproducible procedure for aneurysm morphologic characterization and, in particular, for assessment of aneurysm sac dimensions, but considerable carefulness is required in neck length interpretation.

Functional and radiological outcomes after bridging therapy versus direct thrombectomy in stroke patients with unknown onset: Bridging therapy versus direct thrombectomy in unknown onset stroke patients with 10-point ASPECTS.

BACKGROUND AND PURPOSE: The aim was to assess functional and radiological outcomes after bridging therapy (intravenous thrombolysis plus mechanical thrombectomy) versus direct mechanical thrombectomy (MT) in unknown onset stroke patients. METHODS: A cohort study was conducted on prospectively collected data from unknown onset stroke patients who received endovascular procedures at ≤6 h from symptom recognition or awakening time. RESULTS: Of the 349 patients with a 10-point Alberta Stroke Program Early Computed Tomography Score (ASPECTS), 248 received bridging and 101 received direct MT. Of the 134 patients with 6-9-point ASPECTS, 123 received bridging and 111 received direct MT. Each patient treated with bridging was propensity score matched with a patient treated with direct MT for age, sex, study period, pre-stroke disability, stroke severity, type of stroke onset, symptom recognition to groin time (or awakening to groin time), ASPECTS and procedure time. In the two matched groups with 10-point ASPECTS (n = 73 vs. n = 73), bridging was associated with higher rates of excellent outcome (46.6% vs. 28.8%; odds ratio 2.302, 95% confidence interval 1.010-5.244) and successful recanalization (83.6% vs. 63%; odds ratio 3.028, 95% confidence interval 1.369-6.693) compared with direct MT; no significant association was found between bridging and direct MT with regard to rate of symptomatic intracerebral hemorrhage (0% vs. 1.4%). In the two matched groups with 6-9-point ASPECTS (n = 45 vs. n = 45), no significant associations were found between bridging and direct MT with regard to rates of excellent functional outcome (44.4% vs. 31.1%), successful recanalization (73.3% vs. 76.5%) and symptomatic intracerebral hemorrhage (0% vs. 0%). CONCLUSIONS: Bridging at ≤ 6 h of symptom recognition or awakening time was associated with better functional and radiological outcomes in unknown onset stroke patients with 10-point ASPECTS.

Morphological and immunocytochemical analyses on the effects of diet-induced hypocalcemia on enamel maturation in the rat incisor.

During the maturation stage of amelogenesis, the loss of matrix proteins combined with an accentuated but regulated influx of calcium and phosphate ions into the enamel layer results in the "hardest" tissue of the body. The aim of the present investigation was to examine the effects of chronic hypocalcemia on the maturation of enamel. Twenty-one-day old male Wistar rats were given a calcium-free diet and deionized water for 28 days, while control animals received a normal chow. The rats were perfused with aldehyde and the mandibular incisors were processed for histochemical and ultrastructural analyses and for postembedding colloidal gold immunolabeling with antibodies to amelogenin, ameloblastin, and albumin. The maturation stage enamel organ in hypocalcemic rats exhibited areas with an apparent increase in cell number and the presence of cyst-like structures. In both cases the cells expressed signals for ameloblastin and amelogenin. The content of the cysts was periodic acid-Schiff- and periodic acid-silver nitrate-methanamine-positive and immunolabeled for amelogenin, ameloblastin, and albumin. Masses of a similar material were also found at the enamel surface in depressions of the ameloblast layer. In addition, there were accumulations of glycoproteinaceous matrix at the interface between ameloblasts and enamel. In decalcified specimens, the superficial portion of the enamel matrix sometimes exhibited the presence of tubular crystal "ghosts." The basal lamina, normally separating ameloblasts and enamel during the maturation stage, was missing in some areas. Enamel crystals extended within membrane invaginations at the apical surface of ameloblasts in these areas. Immunolabeling for amelogenin, ameloblastin, and albumin over enamel was variable and showed a heterogeneous distribution. In contrast, enamel in control rats exhibited a homogeneous labeling for amelogenin, a concentration of ameloblastin at the surface, and weak reactivity for albumin. These results suggest that diet-induced chronic hypocalcemia interferes with both cellular and extracellular events during enamel maturation.

Posttranslational modifications of bone collagen type I are related to the function of rat femoral regions.

This study analyzes the relationship between the function of femoral regions in the rat and the extent of collagen type I posttranslational modifications, to assess whether the different functional roles, i.e., mechanical or metabolic, of the bone tissues are related to the molecular structure of the matrix. For this purpose, 18 female, 100-day-old Sprague-Dawley rats were sacrificed, under anesthesia, and their femurs were removed and dissected free of adhering tissue. The spongy bone of the proximal metaphysis and the diaphysis were then selected as regions exerting prevalently a mechanical function, and the spongy bone of the distal metaphysis was selected as mainly related to metabolic function. Bone prepared from these regions was used to extract and purify the major component of the matrix, type I collagen. The content of hydroxyproline, hydroxylysine, glycosylated hydroxylysine, and pyridinium crosslinks was evaluated and the amount of each compound was expressed as a molar ratio to hydroxyproline. The amount of glycosylated hydroxylysine and pyridinium crosslinks in the distal metaphysis are significantly different from the amounts measured both in the diaphysis and the proximal metaphysis. On the contrary, the amounts of the same compounds in the diaphysis and the proximal metaphysis are statistically the same. The amount of free hydroxylysine, however, appears to be different in the proximal metaphysis and in the diaphysis. The conclusion is that matrix composition differs among different skeletal regions according to the main function they exert.

Post-natal bone growth in the semicircular canals of the dog.

Dogs from the same litter, divided into three groups aged 10, 25, and 50 days, received an intraperitoneal injection of tetracycline for two successive days. The temporal bones were fixed, embedded in methylmethacrylate, sectioned in to a single 100 microns thick section along the main axis of the anterior and lateral semicircular canals, grounded by hand to 30 microns and observed at UV light. The new bone tissue is laid down both at the endosteal and endochondral bone of the anterior and lateral semicircular canals. The bone deposition decreases with the age of the animal and earlier at the endosteum than at the endochondral bone.

A topographical analysis of the post-natal bone growth in the cochlea of the dog.

The distribution of post-natal bone deposition was examined in the cochlea of 10-, 25-, 50- and 90-day-old dogs that had been intraperitoneally injected with tetracycline (20 mg/kg) five days before sacrifice. The temporal bones were embedded in methylmethacrylate and sectioned in a single mid-modiolar section 30 microns thick. The post-natal bone deposition occurs both on the periosteal surfaces and on the vascular canals of the endochondral layer until the age of 90 days. Scattered bone deposition is also shown on the endosteal layer of the three turns and on the spiral lamina until the age of 25 and 10 days respectively. The percentage extension of the osteogenetic fronts shows a higher value at the periosteal layer than at the endochondral or endosteal layers.

Intermittent compressive load stimulates osteogenesis and improves osteocyte viability in bones cultured "in vitro".

The effect of mechanical stresses on osteogenesis, the viability of osteocytes and their metabolic activity in organ culture of bones intermittently loaded "in vitro" are reported. Metatarsal bones, isolated from 12-day-old rats, were cultured in BGJb medium (with 10% foetal calf serum, 75 micrograms/ml of ascorbic acid, 100 U/ml of penicillin and 100 micrograms/ml of streptomycin), in humidified air enriched by 5% CO2 and 30% O2, and loaded in our original device for 1/2 an hour at 1 Hz. homotypic isolated and unloaded bones, cultured in the same medium, were taken as controls. The ALP (alkaline phophatase activity) increases in the media of loaded bones in comparison with the control bones. The percentage of viable osteocytes is significantly greater in loaded than in control bones. TEM observations demonstrate that in both loaded and control unloaded bones, osteocytes show well developed organelle machinery and several gap junctions with adjacent cellular processes. In the cells of loaded bones, however, a higher number of cytoplasmic organelles and gap junctions were found. In particular, RER increases twice, gap junctions three times. The induced osteogenesis and the TEM observations demonstrate the suitability of this experimental model and support the recent advanced hypothesis according to which the mechanical loading may exert a trophic function on osteocytes, stimulating both the proteic synthesis in the above-mentioned cells and the cell-to-cell communication. Furthermore, the loading is likely to exert a biological stimulus on osteoblasts via signalling molecules produced by osteocytes.

Cholesteatoma in children: histopathologic findings in middle ear ossicles.

Middle ear ossicles removed during ear surgery in 40 patients were examined in order to compare the histopathologic changes in children with those observed in adults. Bone resorption, mainly localized at the level of the periosteum and haversian canals in adults, was much more extensive in children. Replacement of bone by fibrous granulation tissue was observed in 60% of children's ossicles and in 27% of those belonging to adults. In children, extensive active resorptive osteitis of the ossicles was frequently associated with intensive round cell infiltration, which seems to play an important role in bone absorption and in the aggressiveness of cholesteatoma.

The structure of spongious trabeculae in relation to age in man.

In various bones from 40-50 year old men, numerous osteons were found in spongy trabeculae. As the bones examined are subjected to different mechanical loads, and, in all samples, the osteon frequency appeared to increase with the increase in the trabecular thickness, the endotrabecular osteons was supposed to improve the deep-seated cell metabolism. Because the architecture of the spongiosa changes with age, we studied the endotrabecular osteons in the same bone but in individuals of different age. Human femurs from the collection of our Institute were divided into three groups, corresponding to the 3rd, 5th, and 7th decade of life. Trabeculae were dissected from the proximal end in correspondence of the head, lateral and medial arrangement of the neck. On the serially transverse section the thickness of trabecular tracts with or without osteons, the distance of the deep-seated osteocytes from filtering surfaces, and the orientation of the collagen fibres have been analysed. The mean thickness of the trabeculae decreases with age in the head and lateral arrangement but not in the medial one. The trabecular tracts with osteons are, on the average, significantly thicker than those without them. Almost all endotrabecular osteons show alternate lamellae, notwithstanding that the trabeculae examined are subjected to different type of mechanical forces. These findings would confirm our previous hypothesis that the presence of osteons in the trabeculae responds to metabolic request rather than to mechanical one.

Morphological studies of hypomineralized enamel of rat pups on calcium-deficient diet, and of its changes after return to normal diet.

BACKGROUND: Micro-hardness investigations have shown that rat pups nursed by mothers on a low calcium diet and weaned with the maternal calcium-deficient diet develop hypomineralized enamel. The inorganic and organic components of this enamel, their relationships, and their changes after return to normal diet have been studied by light and electron microscopy. METHODS: The maturation zone of incisor enamel has been studied in: (1) rats nursed for 20 days by mothers on a low calcium diet and weaned for 30 days with the same diet (E1 enamel); (2) rats that after the calcium-deficient diet were fed normal diet for 10 days (E2 enamel); and (3) rats nursed for 20 days by mothers on a normal diet and weaned for 30 days with a normal diet (controls). RESULTS: The results showed that E1 enamel was hypomineralized, as noted by its Azure II-Methylene blue stainability in undecalcified sections, its light staining with the von Kossa method, and its ultrastructure. E1 crystallites, although present throughout the whole enamel, were thinner than those of E2 enamel, which were similar to those of controls. E1 interrod crystallites were thicker in the intermediate than in the dentinal zone and were thicker than rod crystallites. Organic matrix was present throughout the whole E1 enamel. Its organic components (crystal ghosts) had the same shape, arrangement, and organization as those of inorganic crystallites. Crystal ghosts were greatly reduced in E2 enamel and in controls. CONCLUSIONS: The results lead to the conclusions that: (1) E1 enamel is hypomineralized, and its degree of calcification is restored by return to a normal calcium diet; (2) intra- and interprismatic calcification occurs in a different way; (3) crystallite thickness is initially greater in dentinal than in the superficial zone and is reversed as crystallite growth is completed; and (4) loss of enamel proteins is necessary for completion of crystallite growth and not for crystallite formation.

Morphometric analysis of the deposition and mineralization of enamel and dentine from rat incisor during the recovery phase following a low-calcium regimen.

The administration of a low-calcium diet to pups nursed by a mother on the same diet has been shown to induce a slowing of growth. A reduction of the apposition rate of dentine, which was normally mineralized, and a dramatic reduction of the extent of mineralization of enamel, whose organic matrix was otherwise produced in an almost normal amount, was observed in the incisors of these animals. Modifications of the mineral apposition rate of dentine, measured after administration of tetracycline (10 mg/kg), and the thickness and the microhardness of the two tissues, the latter being an expression of the degree of mineralization, were now investigated when hypocalcic pups were restored to a normal-calcium diet for 10 or 60 days. Enamel microhardness was increased by more than 60% after only 10 days of restored diet and had become the same as in the control tissue after 60 days, without any significant increase in thickness. Dentine thickness and mineral apposition rate increased significantly, to become similar to those of the controls after 60 days of restored diet. In dentine there was no significant variation of microhardness between experimental pups and controls, either during the low-calcium diet or the restorative period. These results indicate that the deposition of the organic matrix of enamel is a process independent from that of its mineralization, and that the mineralization of the organic matrix happens by its replacement even a long time after its deposition. In contrast, the deposition and mineralization of dentine are strictly interdependent processes, at least in these experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

[The concentration of osteocalcin in the culture media of bone cultured in vitro subjected to intermittent mechanical load with the addition of 1,25(OH)2D3]. / La concentrazione di osteocalcina nel terreno di cultura di ossa coltivate in vitro sotto carico meccanico intermittente con l'aggiunta di 1,25(OH)2D3.

The osteocalcin concentration decreases in the medium of bones submitted to intermittent mechanical forces in organotypic culture (6). The functional significance of this behaviour is unknown. To investigate the dynamics of the osteocalcin production, we added 1,25(OH)2D3 to the culture medium to stimulate osteoblastic production of the osteocalcin. The bones were isolated from 12 day-old rats, placed in culture medium added with 10(-8) M 1,25(OH)2D3 and subjected 1/2 h daily to an intermittent mechanical load (11.6 Kg/mm2) at 1 Hz frequency. 12, 24 and 48 hours after the loading the alcaline phosphatase activity (p-nitrophenol as substrate) and the osteocalcin concentration (RIA method) were evaluated in the media. The phosphatase activity does not change in the control bones, while it significantly increases in the loaded bones 24 h after loading (fig. 1). The osteocalcin concentration increases significantly in the control bones, with a peak at 24 h; in the loaded ones, it does not increase at 24 h with respect to 12 h, while it increases 48 h after loading, but at a lower level than the control bones. Since the increase of the alcaline phosphatase activity is a sign of new bone production, our results indicate that an osteoid deposition is likely to take place in the loaded bones, not in the control ones. The increase in the control bones of osteocalcin concentration is in agreement with the results of other researches (7), and indicates that the osteoblasts of this experimental system are able to produce osteocalcin under appropriate conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

[Quantitative variations of osteocalcin in the culture media of bones subjected to intermittent mechanical loads in vitro]. / Variazioni quantitative dell'osteocalcina nel terreno di cultura di ossa sottoposte a carico meccanico intermittente in vitro.

A study has been carried out on the dynamics of the osteogenesis induced in vitro by an intermittent mechanical load applied on intact metatarsals isolated from 12 day-old rats. The metatarsals, as soon as isolated, were deprived of both the ends and placed in culture medium (BGJb enriched with 10% FCS, 65 micrograms of ascorbic acid, penicillin, strepto) without a mechanical load. After 4-5 hours, half the bones were placed in our device, described in our previous paper (2), and submitted to a daily cycle of an intermittent mechanical load (11.6 g/mm2) 1/2 h long, at 1 Hz frequency. The remaining bones, used as control, were cultured in the same medium, without any mechanical load. 24, 48 and 72 hours from the first application of the load the bones were fixed, embedded (decalcified or undecalcified) and serially sectioned. The sections were stained with toluidin blu and trichromic Masson-Goldner. On the perimeter of 5 non-consecutive sections of each bone the number of the osteoblasts at 250x, and the nuclear volume of the same cells at 1000x were evaluated. In the culture media the alcaline phosphatase activity (p-nitrophenol as substrate) and the concentration of osteocalcin (RIA) were measured. The number and nuclear volume of the osteoblasts are higher in the loaded than in the control bones (tab. 1). The alcaline phosphatase activity does not vary in the control bones between 24 and 72 h, while it increases in the loaded bones. The concentration of the osteocalcin shows a slight increase at 48 h in the control bones, and a significant decrease int he loaded bones (fig. 1).(ABSTRACT TRUNCATED AT 250 WORDS)

Bone tissue kinetics in the surgically disarticulated dog incus.

The incus of the right ear from 4 growing mongrel dogs was surgically disarticulated and left in the middle ear space. The external auditory canal was then filled with teflon paste and sutured. After 6 weeks (D-6 group) and 13 weeks (D-13 group) the animals were sacrificed. The right experimental incus and the left control one were embedded in methyl methacrylate and sectioned in single 50-microns-thick sections according to the principal axis of the two processes. On the microradiographs of each section we evaluated the thickness of the body and of both processes and the percentage area of the primary channels of the secondary osteons and that of the appositional bone tissue. The thickness of the body and of the two processes was more pronounced in all the experimental incuses, in which 6% (in D-6) and 8% (in D-13) of the total area were occupied by new appositional woven bone. In the body of the D-13 group, 9% of the pre-existing bone was substituted by secondary osteons. The results indicate that the incus react to the variations of mechanical stimuli.

Effect of intermittent mechanical force on bone tissue in vitro: preliminary results.

The structure of metatarsal bones from 18-day-old rats subjected to intermittent mechanical force in organ culture are reported. The application of mechanical force enhances the osteoid thickness and osteoblast number in the periosteum and increases the number of viable osteocytes. These results indicate that (1) the mature bone tissue survives in organ cultures; (2) the mechanical forces better preserve the structure of the osteocytes and stimulate the osteoblasts, and (3) stimulate the osteogenesis.

Candida and stapedial otosclerosis: histopathological findings.

The stapes of 6 patients with stapedial otosclerosis was found to contain fungus hyphae (Candida) in the sectioned specimens. The footplate of all cases and the head of the stapes in 2 of the cases revealed single or multiple erosion cavities containing numerous thin branching PAS-positive fungus hyphae with swollen terminal endings and scanty blastospores. Osteoclasts were not observed; occasional osteoblasts, blue mantles and otosclerotic foci were seen. Four patients had been treated for several years with antibiotics and corticosteroids for recurrent serous otitis media and 1 patient had had frequent catheterization of the eustachian tube. It may be suggested that the Candida infection was a secondary event induced by a general and/or local immunodepressed condition.

The effects of long-term hypoxia on epicardium and myocardium in developing chick embryo hearts.

The consequences of long-term O2 deprivation on heart development were analyzed morphometrically and ultrastructurally, utilizing the hearts of chicken embryos developed under hypoxia from the 3rd to the 18th incubation day. The results indicate that embryos kept under low O2 blood tension do not show disturbances in heart morphohistogenesis, but are characterized by a thicker epicardium and a thinner myocardium than the controls; moreover, both the number and calibre of the heart microvessels are increased. The thickening of the epicardium is due to hyperplasia of the mesothelial cells, increment in calibre of the submesothelial vessels, and to conspicuous perivascular infiltration of blood-derived cells. The thinning of the cardiac muscle seems to be dependent on myocardiocyte hypotrophy and myofibril reduction. The increase in the volume density of myocardium vessels, due to their dilatation and proliferation, may be considered expression of a vascular adaptive reaction to low oxygen tissue concentration.

[The structural organization of the human myocardium: the interrelation between myocardial fibers and interstitial connective tissue]. / Organizzazione strutturale del miocardio umano: interrelazione fra fibre miocardiche e connettivo interstiziale.

The complex tridimensional structure of the human ventricular myocardium has rarely been studied in the past. In the normal heart, in the lapse of time of few weeks of the embryonic life, a radical transformation from a chaotic plexiform organization to a complex tridimensional structure occurs. From then on, the ulterior growth of the myocardial fibres will only be dimensional and quantitative, because the spatial geometry is to be considered definitive. The role of the interstitial connective tissue in following the development of the myocardium, possibly inducing or influencing it, is still unclear. We have performed an histologic study on serial sections of the ventricular mass of 7 human embryos and fetuses, from 5 to 20 weeks of gestational age. The sections have been evaluated for their morphologic characteristics as evidentiated by histochemical (PAS, trichrome, Gomori silver technique) and immunohistochemical (myosin, actin, desmin, myoglobin, vimentin, fibronectin, smooth muscle cell, endothelial factor VIII) stainings. The results show that myocardial growth is mantellar, proceeding from the epicardium toward the endocardium, with progressive structural organization in strata, variably related one to the other depending upon the considered site of the ventricular mass. The interstitium grows in parallel to the myocardial growth, beginning with a thin network surrounding each fibre that progressively in time is transformed in a complexly arranged and more densely packed structure. The collagen fibres appear initially at epicardial level, particularly around the coronary vessels.(ABSTRACT TRUNCATED AT 250 WORDS)

[Survival of bone tissue in organotypic culture under intermittent mechanical loading. Preliminary results]. / Sopravvivenza del tessuto osseo in cultura organotipica, sotto carico meccanico intermittente. Risultati preliminari.

With the aim to study the mechanism of transduction of mechanical stimuli in biological ones we have realized an experimental device for the application of intermittent mechanical forces on bone specimens in vitro. The scheme of the device is reported in Fig. 1. It is constituted by a drive shaft which rotates on eccentric axis (1) supporting a longitudinal bar (2) with the load (3). The latter rests on a piston (4) only during a limited period of every shaft revolution, so that the load becomes intermittent. The bone specimen (5) is placed under the piston and the two are placed in a tube containing the culture medium. This latter is BGJ mod. Fitton-Jackson (Gibco), enriched with fetal calf serum (10%) and ascorbic acid (70 microliters/ml). Right metatarsi from 18-day-old rats were removed aseptically and placed under the piston for 2-6 days after resection of both ends. The homotypic ones, unloaded, were placed in 30 mm Petri dishes, and used as a control. The incubator environment was 5% CO2 in air (A group), or enriched with O2 (25-35%) (B group). At the end of the experimental period the bone specimens were fixed in 4% formalin buffered and treated for conventional histologic methods. In the A group most of the osteocytic lacunae were empty. The osteoblasts disappeared already at the 2nd day; the periosteal fibroblast dedifferentiated and multiplied. The deposition or calcification of osteoid were completely lacking. The application of mechanical load promoted deposition of granular degenerative material around the bone, and the periosteal cells, well differentiated, were surrounded by metachromatic material, which resembles cartilage matrix.(ABSTRACT TRUNCATED AT 250 WORDS)

The structure of the trabeculae of cancellous bone. 2. Long bones and mastoid.

The trabeculae of the mastoid, the upper end of the femur, and the tibia were examined to ascertain whether they contain vascular channels according to a pattern similar to that observed in the calcaneus. The trabeculae were serially sectioned in transverse planes. Each section was microradiographed and photographed under ordinary and polarized light. On the photos of the individual sections (1) the number of the vascular channels, (2) the thickness of the trabecular segments with or without osteons, and (3) the maximum distance of the osteocytic lacunae from filtering surfaces (i.e., haversian canal walls or trabecular surfaces), were evaluated. About 80% of the vascular channels are haversian. Their frequency increases through the increase of the trabecular thickness and reaches 100% in those thicker than 428 microns. The distance of the deep-seated osteocytes from filtering surfaces appears almost the same in the thinner trabeculae, devoid of osteons, and in the thicker ones, containing osteons. Evidence is provided that osteons are present in numerous spongy trabeculae. Osteon formation is strictly related to the trabecular thickness so that the distance of the osteocytes from filtering surfaces does not exceed the critical value of 230 microns (in the mastoid). These findings are in agreement with those recorded in the calcaneus spongiosa. As the trabeculae studied in this research and those of the calcaneus are submitted to different mechanical loads, the main function of the endotrabecular osteons is conceivably to improve the deep-seated cell metabolism rather than the mechanical resistance of the trabeculae. On the other hand, the circumstance that most of the osteons are secondary indicates that they participate to the renewal of bone tissue.