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Normal Infant Anatomy: Correlated Real-Time Sonograms and Brain Specimens

Asterios Pigadas 1 An investigation of the identifiable real-time sonographic features of the normal Joseph R. Thompson 1 infant brain in the horizontal, coronal, inclined coronal, and midsagittal planes was Gerald L. Grube2 undertaken. Correlations were made of sonograms of intact in vitro, correspond­ ing brain sections, and sonograms in vivo. A large number of anatomic structures could be consistently depicted including cisterns, fissures, , tentorium cerebelli, ventricles, brainstem, , basal ganglia, thalami, and . Pulsa­ tions of intracranial arteries, visible by real-time sonography, were of considerable help in identifying various structures. The investigation provides a reference of sonographic anatomy of the brain displayed in four clinically useful imaging planes.

Early investigators of diagnosti c sonography were faced with th e probl ems of small-aperture unfocused transducers. In 1967, White et al. [1] summari zed these problems. In 1972, Kossoff and Garrett [2] reported intracrani al detail in fetal echograms using a weakl y focused 2 MHz transducer. They subsequently published a sonographic atl as of th e normal brain of infants using a focused 3 MHz transducer-contact C.A.L. echoscope [3]. McRae [4] and White [5], how­ ever, questioned th eir ability to identify those intracranial structures. In 1976 , Heimberger et al. [6], using large-aperture f oc us ~9 transducers, managed to display the outlines of th e th alamus, internal capsule, and substanti a ni gra in isolated excised brains. Recently Johnson et al. [7] showed sonographic anatomy in the axial pl ane and examples of intraventric ul ar hemorrhage in hi gh ri sk infants using B-mode contact transducers. The advent of versatil e real-time transducers has stimulated us to do more detailed imaging in several pl anes to establi sh a basic anatomy for use in clinical work. Real-time as opposed to stati c scanning was chosen because: 1. Recognizabl e pulsati ons of th e intracrani al vessels within fi ssures and cisterns and of the choroid pl exuses within the ventric les provides easier identi­ Received October 26. 1979; accepted after revision Febru ary 10, 1981. fication of these structures. Presented at the annual meetings of the Amer­ 2 . The real-time probe can be easil y maneuve red so th at the ultrasonic beam ican Insti tute of Ullrasound in Medicine, Montreal, is perpendicular to the intracranial structure under stu dy, th erefore receiving August 1979 and the Western Neuroradiological stronger reflecting echoes for better images. Sociely. Carm el, Ca lifornia, October 1979. Skolnick et al. [8 ] used a servo-controlled real-time scanner to detect dilated ' Deparlment of Radiati on Sciences, Secti on of Neuroradiology, Lorn a Linda Universi ty School of ventricles and correlated th e findings with computed tomography. We th ought it Medic ine, Lorn a Linda, CA 92350. Address reprint would be more useful to correlate real-time sonography and anatomic secti ons, requests to J . R. Thompson. in pl anes avail abl e for c linical examinati on. 2Department of Radiation Sciences, Section of Diagnosti c Ullrasound, Lorn a Li nda University School of Medicine, Lorn a Linda, CA 92350. This paper appears in the July / August 1981 Materals and Methods issue of AJNR and the October 1981 issue of AJR. The sonographic examinati ons were performed by using either a linear phased array AJNR 2:339-344, July / AU9ust 1981 0 0 195- 6 108/ 8 1/ 0204 - 0339 $00.00 transducer operating at 2.25 MHz and d isplaying 84 fan-shaped images at a frame rate © American Roentgen Ray Society of 30 / sec (Vari an V-3000), or an annular array transducer operating at 2.25 M Hz ± 15% 340 PIGADAS ET AL AJNR:2, July/ August 1981

Fig. 1.- Transducer placemenl for multiplanar imaging.

A B

A B c Fig. 2.-Horizontal plane at level of c hiasmatic c istern. A, In vitro real­ Ten = tentorium. Optic chiasm (black arrow); aqueducl of Sylvius (white time sonogram. B , Anatomic sectio n . C, In vivo. CC = chiasmati c c istern ; Int arrow); temporal horn (arrowhead). F = interh emispheric fi ssure; Syl F = sylvian fissure. M es = mesencephalon;

and displaying 24 0 angle sector im ages at a selectable frame rate (Varian V-3000) was placed over the temporal squama for the of 1 or 12 / sec (Xerox 1505-4). horizontal planes and over the anterior fontanelle for the coronal, Three excised brain specimens were fi xed in formalin for 2 weeks inclined coronal, and midsagittal pl anes (fig. 1). Adequate ultrasonic and th en immersed in tap water. Care was taken to exclude air gel was appli ed between th e probe and skin for optimal acoustical bubbles from th e fi eld of view. Th e probe (Xerox 1505-4) was then coupling. No sedati on or anesth esia was necessary. Postprandial placed over th e temporal lobe and serial images were obtained in scanning or the use of a pacifier was adequate to obtain optimal th e hori zontal plane at 1 cm increments from the level of the lower im ages. All real-time sonograms were displayed on a vid eo screen cerebellum to th e high convexities of the . For th e next and permanent records were made on Polaroid film and video tape. specimen, th e probe was pl aced in a position assumed to simu late th e anteri or fontanelle and seri al 1 c m images were obtained in the coronal plane. For the third specimen, th e transducer was placed Horizontal Plane in the position of th e anterior fontanell e and th e beam was directed toward the giving a modified coronal im age (inclined Level of the coronal plane). Fin all y, images were obtained with th e beam di­ The chiasmatic (suprasell ar) c istern is shown as a penta­ rected in the midsagittal plane. After the in vitro scanning was gonal, strongly echogenic structure in the center of the completed, the specimens were sectioned in the corresponding planes. image, with the similarly echogenic interhemispheric and Fifteen normal infants aged up to 15 months (average, 5 months) Sylvian fissures originating from the anterior and both lateral were also examined. Each had a normal CT study. The probe corners of the pentagon (fig. 2). Posteriorly, the circumme- AJNR:2. July / August 1981 INFANT CRANIAL ANATOMY 3 41

A B c Fi g. 3.-Hori zontal plane at level of cerebral pedunc les. A, In vitro. B, ventri cle; Int F = interhemispheric fi ssure. of temporal horn Anatomic secti on. C, In vivo. AC = ambient cistern; Cer V = cerebell ar ( arro whead); aqueduc t ( arrow ). vermis; Cir S = circ ular sul cus; qc = quadri geminal cistern; 3 = third

A B c Fi g . 4 .-Horizontal plane at level of thalami . A , In vitro. B, Anatomic Cir S = circ ul ar sulcus. ("); corpus call osum (long arrow) ; anterior sec ti on. C, In vivo. T = trigone; Tha = th alamus; vgc = ve in o f Galen c istern ; horn s ( short arrows ). sencephalic cisterns are continuous with the posterior cor­ can be seen to be pulsating within th e interpeduncul ar ners of the c isternal pentagon and outline a V-shaped ane­ c istern . choic structure, the mesencephalon. Pul sati ons are seen within the Sylvian, in te rhemispheri c , In the center of the pentagon, a low-amplitude-echo struc­ and circ ummesencephali c c istern s from th e middle cerebral , ture is constantly seen and represents the optic chiasm. anteri or cerebral, and circ ummesencephalic arteri es, re­ Th e relatively hypoechoic optic c hiasm appears to be di­ spectively. Posteri orl y, th e low amplitude echogeni c cere­ vided by a thin midline linear echogenic structure which can bellum is outlined by obliquely ori ented echoes representing be shown to be the anterior inferior part of . th e leaves of th e tentorium . Th e frontal and temporal lobes Immediately ventral to th e mesencephalon, the basil ar artery are depi cted by low amplitude echoes. 34 2 PIGADAS ET AL. AJNR:2. July / August 1981

A B c Fig. 5. -Horizontal plane at level of . A, In vitro. B, Anatomic secti on. C, In vivo. Lateral wall of lateral ventric les (paramedian echoes); fa lx cerebri (m idli ne echo).

Level of the Cerebral Peduncles Level of Lateral Ventricles

Th e anechoic V-shaped mesencephalon is in the center The midline, echogenic, interhemispheric fi ssure is seen of th e im age, with th e constantly seen single strong echo of accommodating the fal x cerebri (fig. 5). Parallel , paramedial, the aqueduct of Sylvius in the center of the tectum (fig. 3). linear echogenic structures are also seen which represent Posteriorl y, th e echogenic tentori al hi atus outlines the su­ th e lateral walls of the lateral ventric les. The inner tabl e of peri or vermis, which is separated from th e mesencephalon the is sharpl y defined. Soft echoes interposed by th e quadrigeminal cistern . The lateral margins of the between th e falx cerebri and lateral wall of the lateral ven­ mesencephalon are outlined by th e ambient c istern s, whic h tricle represent combination echoes of the medial wall of th e are situated medial to th e parahippocampal gyri. The am­ lateral ventricle and of the parietal cortex. bi ent cistern s appear to join the c horoid pl exuses of the temporal horn s by their continuation with th e transverse Coronal Plane cerebral fi ssures. The linear echogeni c structure in front of Level of the Chiasmatic Cistern the mi dbrain represents a combinati on of third ventricle and interh emispheric fi ssure. The circ ul ar sulci are also seen as The anechoic optic chiasm is readily seen within the strong c urvilinear pul satile echoes at the medial aspects of strongly echogenic and pulsatil e chiasmatic c istern (fig . 6). th e Sylvian fi ssures. Superi orly, one can see th e midline echo of th e third ventri­ cle. The roof of the third ventricle refl ects strong echoes due to th e . Just above it, a thin, anec hoic , Level of the Thalami hori zontal stri pe is constantly seen whic h represents the corpus call osum. Superiorly, two pulsatile echogenic struc­ The midline echogenic third ventricle is seen in the center tures, th e peri callosal and call osomarginal arteri es, can be of th e image (fig. 4). Near its anteri or end, the forni x, a identified within the peri callosal and cing ul ate sulc i. Lat­ bulbous hyperechoic structure, separates the posteri or erall y, the c ircular sul c i mark the outer margins of th e basal parts of the frontal horns and blends with th e echoes of the gangli a and thalami. septum pelluc idum and interh emi spheri c fi ssure. On each side of th e third ventricle, a well defined , low amplitude, oval Level of Crural and Interpeduncular Cisterns structure represents the th alamus. Just posteri or to th e thalami , the transversely ori ented, echogeni c, retrothalami c The centrall y placed interpedunc ul ar cistern " stands out" fi ssures run toward the choroid plexuses of the ventric ul ar due to strong refl ections from the pulsations of the basilar atri a and outline the . The echogenicity of the artery (fig. 7). Just inferi or to this c istern , a faintly outlined lentiform nucleus is simil ar to that of th e th alamus. The two brai nstem is seen. On each side of th e interpeduncular structures are occasionall y seen to be separated by the cistern , th e mediall y convex c rural c istern outlining the posteri or limb of the intern al capsul e. Laterall y the basal uncus continues laterally and bl ends with th e echoes of the ganglia and th alami are distinctl y outlined by th e circ ul ar c horoid pl exus of th e temporal horn . The low amplitude su lci. thalami c echoes are seen above the interpedunc ular cistern AJNR:2. July / Augusl1981 INFANT CRANIAL ANATOMY 343

Fi g . 5 .-Coronal plane al level of chiasmalic cislern . A, In vitro. B, Analomi c sec lion. C, In vivo. BG = basal ganglia; CC = chiasmalic cislern ; C. c = cingul ale sulcus; Cir S = circul ar sul cus; p . p = peri call osal sul cus; 3 = third ventric le; oc = optic c hiasm. Corpus callosum (arrow).

B c Fig . 7 .- Coronal plane at level of crural and in terpeduncular c istern s (IC). A, In vilro. B, Anatomic specimen. C , In vivo. Cr C = crural cistern ; Tha = ; C. c = cingulate sulcus; p . p = pericall osal sul cus. Corpus callosum (arrow).

and, more superiorly, th e lateral ventricles, corpus callosum, Anterior to th e brainstem are the echogenic and pul satil e and supracallosal sulci. interpedunc ul ar, prepontine, and medullary c istern s. Pos­ teri or to the brainstem are the relatively high amplitude echoes of the cerebell ar vermis. Inclined Coronal Plane

The inclined coronal plane (fig. 8) is extremely helpful in Discussion outlining the posterior fossa. The obliquely oriented echo­ The echogeni c ity of an intracranial structure depends on genic tentorial leaves outline the upper cerebellum, which is its abrupt interface with neighborin g structures. Structures characterized by uniform, low to medium amplitude echoes. with abrupt interfaces in clude: (1) lateral wall s of lateral Th e fourth ventricle is a round and highly echogenic midline ventricles against th e ; (2) vessels and structure. nerves within fi ssures and c istern s; (3) the myriad frondlike interdigitati ons of th e ventric ul ar choroid pl exus within the cerebrospinal fluid; and (4) falx cerebri and tentorium Midsagittal Plane against cerebrospinal fluid. Fi ssures, cistern s, choroid The midsagittal plane (fig. 9) exquisitely outlines midline pl exus, lateral ventricular wall s, falx, and tentoriu m, there­ structures such as th e third ventricle, corpus callosum, and fore, are always depi cted as strongly echogeni c structures brainstem. It is interesting that the third ventricle is depicted which can be used reli ably as anatomi c landmarks. Th e in this plane as an anechoic structure except for the massa .,c rowded ." strongly echogenic appearance of c isterns re­ intermedia. Its anechoic appearance is probably explained sulting from interposition of , veins, and pulsating by th e sagittal orientation of the walls of the third ventricle arteries is in contrast to the usual conception of their bei ng and the depth of cerebrospinal fluid (CSF) within it. Often " empty " CSF-filled spaces on computed tomography or the optic and infundibular recesses of the third ventricle can pneumoencephalography. be seen. Inferiorly, th e mesencephalon, pons, and medulla In our experi ence, the midline third ventricle creates a oblongata are seen as fairly uniform, hypoechoic structures. single linear echo due to its c losely spaced ependymal 344 PIGADAS ET AL. AJNR:2. July / August 1981

A B c Fig. 8. - lnc lined coronal plane through anteri or fontanell e. w ith beam directed toward fourth ventric le. A, In vitro. B, Anatomic section. C, In vivo. Tr F = transverse fissue; mes = mesencephalon; Ten = tentorium; Tha = thalamus; 3 = third ve ntric le; 4 = fourth ventric le.

A B c Fi g . 9 .- Mid sagittal plane. A, In vitro. B, An atomic section. C, In vivo. Cer V = cerebell ar vermis; C, c = cingul ate sulc us; Cli = c livus; mes = mesencephalon; oc = optic chiasm; p = pericall osal sulcus ; po = pons; 3 = third ventric le; 4 = fourth ventric le. Massa intermedia (short arrow ); corpus call osum (long arrow ).

surfaces. This is similar to th e midline echo pattern of th e REFERENCES uterine cervical canal on pelvic sonography. A slitlike ane­ choic third ventricle, in fact, represents an early dilatation of its lumen. The fourth ventric le is depi cted as a rounded 1. White ON , Cl ark JM, White MN. Studies in ultrasonic echoen­ echogeni c structure due to th e enorm ous reflecting echoes cephalograph y; VII. General princ iples of recording information in ultrasonic B and C scanning and th e effects of scatter, of th e c horoid plexus and th e rh omboid ventric ul ar wall s. refl ecti on and refracti on by cadaver on this information. Structures with homogeneous texture such as brain stem, M ed 8 iol Eng 1967;5;3-1 4 th alamus, and corpus call osum , on th e oth er hand, produce 2. Kossoff G, Garrett WJ . In tracranial detail in fetal echograms. uniform low amplitude echoes. Invest Radiol 1972;7: 159 -1 63 The far side of the sonographic image (within th e focal 3. Kossoff G, Garrett WJ , Radavanovich G. Ultrasoni c atl as of d istance of the transducer) always shows more reli abl e normal bra in of infant. Ultrasound Med 8 io/1974 ; 1 :259- 266 inform ati on th an th e near side due to th e inherent limited 4. Mc Rea DL. Letters to th e editor. Ultrasound M ed 8 io/ 1975;1 : near-field resolution of th e phased-array real-time trans­ 41 1 ducers. Scanning through both temporal sq uama, th erefore, 5. White ON . Letters to the editor. Ultrasound Med 8 iol 1975;2: is essential in order to obtain precise inform ati on from both 45-46 6. Heimburger RF , Fry FJ , Franklin TO , et al. Two dimensional hemispheres. While stati c scanning does show intracrani al ultrasound scanning of excised brains: I. Normal anatomy. structures, real-time sonography has th e advantage of quick Ultrasound Med 8 io/ 1977;2:279- 285 and accurate structure identificati on because of vascular 7. Johnson ML, Mack LA, Rumack CM , Frost M , Rashbaum C. B­ pu lsati ons and instantaneous displ ay. mode echoencephalography in the normal and high risk infant. AJR 1979;133:37 5- 381 ACKNOWLEDGMENTS 8. Skolnic k ML, Rosenbaum AE, Matzuk T, Guthkelch AN, Hein z We thank Abraham Lu for performing th e brain secti oni ng , Marie ER. Detection of dil ated cerebral ventric les in infants: a correl­ De Lange for the RTU scanning, and Sheil a Wi ll s for assistance in ative study between ultrasoun d and computed tomography. preparing the manuscri pt. Radiology 1979; 131 :447-451