Frans W. Zonneveld

Comparative review of the human bony labyrinth

The bony labyrinth inside the petrous part of the temporal bone houses the organs of hearing and balance. Being functionally linked with sensory control of body movements and located in a part of the basicranium that is closely associated with the brain, this structure is of great interest in the study of human evolutionary history. However, few aspects of its morphology have been studied in nonhuman primates. This review compares the bony labyrinth of humans with that of the great apes and 37 other primate species based on data newly acquired with computed tomography combined with previous descriptions. With body mass taken into account, consistent differences are found between the size of the semicircular canals in humans, the great apes, and other primates. In particular, the arcs of the anterior and posterior canals are larger in humans than in the African apes. The functional implications of semicircular canal dimensions for registering angular head motion are evaluated in relation to locomotor behavior. Biophysical models, comparative studies, and some neurophysiological experiments all support a link between semicircular canal size and agility, or more specifically the frequency contents of natural head movements, but the evidence on the exact nature of this link is ambiguous. It is concluded that any link between the characteristic dimensions of the human canals and locomotion will be more complex than a simple association with the broad categories of quadrupedal vs. bipedal behavior. The functionally important planar orientations of the semicircular canals are similar in humans and the African apes as well as in many other species. In contrast, other aspects of the human labyrinth differ markedly in shape, following a pattern that seems to reflect the characteristic architecture of the human basicranium. Indeed, it is found that labyrinthine and basicranial shape are interspecifically correlated in the sample, and in most respects the human morphology is consistent with the general trend among primate species. Differences in brain growth and development are proposed as the predominant factor underlying both the unique shape of the human labyrinth as well as the interspecific labyrintho-basicranial correlations.

The bony labyrinth of Neanderthals

This paper presents a comprehensive comparative analysis of the Neanderthal bony labyrinth, a structure located inside the petrous temporal bone. Fifteen Neanderthal specimens are compared with a Holocene human sample, as well as with a small number of European Middle Pleistocene hominins, and early anatomically modern and European Upper Palaeolithic humans. Compared with Holocene humans the bony labyrinth of Neanderthals can be characterized by an anterior semicircular canal arc which is smaller in absolute and relative size, is relatively narrow, and shows more torsion. The posterior semicircular canal arc is smaller in absolute and relative size as well, it is more circular in shape, and is positioned more inferiorly relative to the lateral canal plane. The lateral semicircular canal arc is absolutely and relatively larger. Finally, the Neanderthal ampullar line is more vertically inclined relative to the planar orientation of the lateral canal. The European Upper Palaeolithic and early modern humans are most similar, although not fully identical to Holocene humans in labyrinthine morphology. The European Middle Pleistocene hominins show the typical semicircular canal morphology of Neanderthals, with the exception of the arc shape and inferiorly position of the posterior canal and the strongly inclined ampullar line. The marked difference between the labyrinths of Neanderthals and modern humans can be used to assess the phylogenetic affinities of fragmentary temporal bone fossils. However, this application is limited by a degree of overlap between the morphologies. The typical shape of the Neanderthal labyrinth appears to mirror aspects of the surrounding petrous pyramid, and both may follow from the phylogenetic impact of Neanderthal brain morphology moulding the shape of the posterior cranial fossa. The functionally important arc sizes of the Neanderthal semicircular canals may reflect a pattern of head movements different from that of modern humans, possibly related to aspects of locomotor behaviour and the kinematic properties of their head and neck.

Quantification of orbital and mid-facial growth retardation after megavoltage external beam irradiation in children with retinoblastoma

PURPOSE The late side effects of external beam irradiation in patients with retinoblastoma such as orbital bony growth retardation, are a serious problem in adolescence. Therefore, a quantitative study was performed to investigate the late effects of irradiation on orbital growth in patients with retinoblastoma. METHODS The orbits of 68 patients with retinoblastoma, 52 bilateral and 16 unilateral, were divided into two treatment groups: radiotherapy alone, 77 orbits; and radiotherapy + enucleation, 43 orbits. Follow-up time was 12 to 240 months (mean, 95 months) in group 1 and 27 to 216 months (mean, 97 months) in group 2. These groups were subdivided further into age groups at which radiotherapy was given. The morphometric measurements of these groups were compared. RESULTS The authors showed that irradiation causes a significant growth retardation when compared with the growth of nonirradiated orbits (P<0.001). They also demonstrated that radiotherapy in children younger than 6 months of age is more damaging to the orbital growth than at an older age (P<0.01). Finally, the authors showed that secondary enucleation does not have an additive growth-retarding effect. CONCLUSION Orbital growth retardation in patients with retinoblastoma after radiotherapy is influenced mainly by the age at which irradiation is given and is defined at 6 months. Theoretically, it would be desirable to postpone irradiation in children until they are older than 6 months of age if possible. The irradiation effect on these orbits is not enhanced by enucleation.

Using diagnostic radiology in human evolutionary studies

This paper reviews the application of medical imaging and associated computer graphics techniques to the study of human evolutionary history, with an emphasis on basic concepts and on the advantages and limitations of each method. Following a short discussion of plain film radiography and pluridirectional tomography, the principles of computed tomography (CT) and magnetic resonance imaging (MRI) and their role in the investigation of extant and fossil morphology are considered in more detail. The second half of the paper deals with techniques of 3‐dimensional visualisation based on CT and MRI and with quantitative analysis of digital images.

A New and Validated CT-Based Method for the Calculation of Orbital Soft Tissue Volumes

PURPOSE There is no consensus as how to calculate orbital soft tissue volume based on CT or MRI scans. The authors sought to validate their technique and to assess the intraobserver and interobserver variability of their calculations of bony orbital volume (OV), orbital fat volume (FV), and extraocular muscle volume (MV) on CT scans of humans. METHODS The authors calculated these volumes with the use of a manual segmentation technique on CT scans with commercially available software. Two observers (one of them masked) calculated the orbital soft tissue volumes in a CT scan of a phantom constructed of dry skull, butter, and chicken muscle. These calculations were compared with previously taken standard volume measurements of these materials. Repetitive calculations on one CT scan by the same observer were compared. Soft tissue volumes taken from 10 orbital CT scans were calculated by two observers and compared. From the data acquired, intraobserver and interobserver variability was calculated. RESULTS Outcomes of these calculations using this software approximated the volumes of the phantom measured with standardized techniques. Accuracy of the phantom calculations between the two observers varied from +0.7% to -0.7% for FV and between -1.5% and -2.2% for MV. Mean differences between the repeated calculations were smaller than 5%. The intraclass correlation coefficient varied from 0.961 to 0.999. CONCLUSIONS Calculating orbital soft tissue volume using a manual segmentation technique for CT scans is a reliable and accurate tool.

Computed Tomography in the Assessment of the Postenucleation Socket Syndrome

To gain a deeper insight into the cause of the postenucleation socket syndrome, high-resolution computed tomography (CT) was performed in 22 anophthalmic patients before insertion of an intraorbital implant. The anatomy of the normal and the anophthalmic orbits was compared. Computed tomographic scans were made either in the sagittal and the coronal plane or in the sagittal and transverse plane. The authors discovered a sagging and retraction of the superior muscle complex and a downward and forward redistribution of orbital fat. Finally, an upward displacement of the distal end together with a retraction of the inferior rectus muscle was found. These phenomena were measured and appear to cause a rotatory displacement of orbital contents from superior to posterior and from posterior to inferior which is best demonstrated in the sagittal plane. This redistribution of orbital contents can explain the sequelae of the anophthalmic orbit. No signs of orbital fat atrophy could be demonstrated. With this knowledge, the proper treatment of patients with a postenucleation socket syndrome is ascertained.

RARE TEMPORAL BONE PATHOLOGY OF THE SINGA CALVARIA FROM SUDAN

Evidence has recently accumulated that the Singa calvaria from Sudan probably dates from Oxygen Isotope Stage 6 (>130 ka). Morphological studies have indicated a mixture of archaic and more modern human traits, but such analyses are complicated by the possibility that the vault is pathologically deformed, although the exact etiology has not been established. Now computed tomography (CT) has revealed that the right temporal bone lacks the structures of the bony labyrinth. The most likely cause of this rare pathological condition appears to be labyrinthine ossification, in which newly deposited bone obliterates the inner ear spaces following an infectious disease or occlusion of the labyrinthine blood supply. A possible cause of vascular compromise could have been the presence of an expanding acoustic neuroma in the internal acoustic meatus, which is suggested by a significantly wider right meatus compared with the left side. Interestingly, labyrinthine ossification is also consistent with the controversial diagnosis that an anemia caused the characteristic diploic widening at the parietal bosses, because prime etiological factors of ossification are among the common complications of some of these blood diseases. CT examination of the vault and a review of the literature suggest that a blood disorder may well have caused the unusual parietal morphology. Given the nature of these pathological conditions, the Singa individual must have experienced a period of considerable disability. The morphological evidence from the normal bony labyrinth on the left side and from the CT evaluation of the vault is consistent with the interpretation of Singa as a late archaic hominid or an early representative of Homo sapiens drawn from a population which might be directly ancestral to modern humans.

Relationship in hypoplasia between the masticatory muscles and the craniofacial skeleton in hemifacial microsomia, as determined by 3-D CT imaging.

The purpose of this study, based on three-dimensional (3-D) computed tomographic (CT) reconstructions, was to evaluate the relation between underdevelopment of masticatory muscles and hypoplasia of the craniofacial skeleton in hemifacial microsomia (HFM). In 25 patients with HFM and 19 control patients the volumes of the masseter, the temporal, and the medial-pterygoid and lateral-pterygoid muscles were measured on the basis of CT scans, using three-dimensional segmentation and voxel addition. The size and shape of the craniofacial structures were classified, using three-dimensional imaging based on CT scans. Contiguous 1.5-mm computed tomography scans were made with a Philips Tomoscan 350 and processed by a Cemax 1500X 3-D workstation. Using the Pearson product moment correlation coefficient, the Pruzansky/Kaban classification system, the new Craniofacial Deformity Scoring System, Cranial Deformity Scoring System, and Mandibular Deformity Scoring System (MDS) demonstrated correlation coefficients with the “masseter muscle percentage” varying from 0.71 to 0.81 (P < 0.05), with the medial pterygoid muscle percentage correlation coefficient varying from 0.43 to 0.56 (P < 0.05), with the lateral pterygoid muscle percentage correlation coefficient varying from 0.55 to 0.61 (P < 0.05), and with the temporal muscle percentage correlation coefficient varying from 0.67 to 0.84 (P < 0.05). The normal right/left difference in volume of the masticatory muscles of the control patients, calculated as a percentage of the total, demonstrated small differences of 3.4% to 4.8%. Bony malformations are associated with underdevelopment of the masseter and the temporal muscles, and demonstrate a tendency toward a clear relationship. The degree of muscular underdevelopment of the different muscles of mastication in one patient could vary widely. The normal right/left difference of the masticatory muscles of the control patients is minimal. The volume of the masticatory muscles of the nonaffected side does not demonstrate a compensatory effect in patients with HFM.

A three-dimensional smooth surface analysis of untreated crouzon’s syndrome in the adult

This study compares the three-dimensional smooth surface shape of five adult patients with Crouzons disease with nine normal skulls. A new analysis method is described which is based on smooth surface curvature. Surface samples are subdivided by a common ridge curve structure. Three-dimensional images of an average normal and an average Crouzon skull are illustrated. Comparisons between groups are performed on landmarks, as well as ridge curve and surface patch midpoints. There was as much discriminant information in the ridge curves and surface patches between landmarks as there was at the landmarks themselves. When compared with normal samples, the Crouzons syndrome sample exhibits the following major characteristics: The mid-face is concave and wide, with the piriform aperture in the center more recessed than the perifery of the mid-face. The forehead is recessed above a frontal sinus bulge. The orbits are shallow, wide, concave, and tilted interiorly with a mild hypertelorism. These data suggest that advancement of large, one-piece osteotomy segments will not produce a normal face, and a multisegment approach should be considered.

Bony orbital development after early enucleation in humans

AIM To analyse the extent of bony orbital volume reduction after enucleation in humans. METHODS Volumetric studies on bony orbital volumes based on three dimensional reconstructions acquired from high resolution computed tomograph (CT) scans were performed in 29 patients with acquired anophthalmia and four patients before enucleation (controls). Eight patients (follow up 25–52 years) were enucleated in childhood aged between 0.4 and 8 years (group I), 21 in adulthood aged between 15 and 53 years. Fifteen of these patients (group IIa) had long standing anophthalmia (follow up 7–53 years), six patients (group IIb) were enucleated 9 months to 4 years before CT. RESULTS Bony orbital volumes were reduced in all patients with long standing anophthalmia. The median percentage reduction in enucleated orbits was 7.0% in group I, 3.8% in group IIa, and 1.9% in group IIb. In patients with long standing anophthalmia (I and IIa) the reductions were statistically significantly different (p <0.01) from zero. There was some evidence of a correlation between orbital volume reduction and age at enucleation (rho = 0.36, p = 0.09, Spearman rank correlation coefficient) and a statistically significant correlation between volume reduction and time interval since enucleation (rho = −0.5, p = 0.003). Clinically none of the patients showed significant facial asymmetry. CONCLUSIONS These data provide strong evidence that enucleation both in children and adults is associated with a reduction of bony orbital volume and that this decrease in volume is associated with increasing time. However, the reduction is smaller than generally assumed and does not cause obvious facial asymmetry. It is more related to the time interval since enucleation than the age at enucleation, which makes a mechanism of volume adaptation more likely than just retardation of growth.