Real-Time Sonographic Sector Scanning of the Neonatal Cranium: Technique and Normal Anatomy
William P. Shuman 1 A commercially available wide field of view real-time mechanical sector scanner can James V. Rogers1 be used t o image the neonatal cranium. Because of the small transducer head size, the 1 Laurence A. Mack . 2 open anterior fontanelle can function as an acoustic window. By thus avoiding bone, higher f requency transducers may be used to improve image resolution. Infants may Ellsworth C. Alvord, Jr 3 be scanned quickly without sedation in their isolettes in the neonatal intensive care David P. Christie2 unit. Sterility of the infant environment is maintained by placing the transducer in a surgical glove. Using this technique, detailed normal anatomy can be seen such as vascular structures, caudate nucleus, thalamus, third ventricle, cavum septum pelluci dum, and the thalamocaudate notch. Angled coronal and sagittal sonographic anatomy is correlated with neonatal cadaver brain sections sliced in similar planes centered on the anterior fontanelle.
The mechanical sector scanner has advantages over other real-time devices including improved image resolution, a wider field of view, and a small er area of transducer skin contact. These unique assets are particularly appli cable to th e evaluati on of the neonatal cranium. The small transducer of a sector scanner can easil y be held in contact with the open anterior fontanell e using it as an acousti c window. This window avoids bone and makes possible the use of a higher frequency transducer resulting in improved resolution. We report our technique for neonatal crani al sonography usin g a mechanical sector scanner. Norm al intracranial anatomy seen in angled coronal and sagittal planes is presented along with correlating neonatal cadaver specimens.
Materials and Methods
Seventy-two neonates who were clinicall y suspect for intracran ial hemorrhage were examined in their incubators in the neonatal intensive care unit (N ICU) usin g a mechanical sector scanner (ATL Mark III Imaging System). This has three internall y focused 5 MHz transducers positioned on a rotating element. Each transducer is acti vated through th e Receive d October 16, 1980; accepted aft er same 90 0 arc producing 18 to 45 im ages/ sec. The tran sducer skin contact area is 1.5 x revision January 15, 1981 1.5 cm. Images are generated in a circul ar sector format producing a pie-shaped field of , Department of Radiotogy, University Hospitat, view with the narrow, sli ghtly truncated end representing th e small area of skin contact (fig. SB-05, University of Washington, Seattte, WA 1). Images are processed through a real-time digital scan converter and projected on a 98185. video display system. A freeze frame mode is avail able so that video im ages may be 2 Department of Radiology, Harborview Medi recorded on 70 mm film. cal Center, ZA-65, 325 Ninth Ave., Seattle, WA In the NICU , the real-time sonographic unit is positioned beside th e infant incubator. It is 98104. Address reprint requests to L. A. Mack. not necessary to move the incubator or adjacent support eq uipment or to disturb the 3 Department of Pathology, Universi ty Hospital, oxygen and temperature controll ed environm ent. A small amount of aqueous acousti c RJ -05, Un iversity of Washington, Seattle, WA 98195. coupling gel is placed in the thumb of a steril e size 8 latex surgical glove. The transducer head is inserted into the thumb of the glove whic h then serves as a sterile barri er (fig . 2). This article appears in th e July/ August 1981 AJNR and October 1981 AJR. A small amount of acousti c gel is appli ed to the an teri or fontanell e. The glove-encased transducer is passed through th e port of the incubator and placed on th e anteri or fontanelle AJNR 2:349-356, July / AU9ust 1981 0 195-6 108 / 8 1/ 0204-0349 $00.00 in the coronal plane (fi gs. 3 and 4). By rocking the tran sd ucer back and forth , th e ve ntricul ar © Am erican Roentgen Ray Society system as well as peri ven tricul ar struc tures can be examined (fig. 5). Freeze-frame images 350 SHUMAN ET AL. AJNR:2, July/ Augusl 1981
Fig . 3 .- Transducer head is placed on anterior fontanell e and rocked back and forth to sweep sonographic beam through cerebral tissue. Fig. 1.-End-on frontal diagram of hand-held unit. The three transducers ro tate in a complete circ le but are acti vated through only a 90° arc produc ing a seclor image which widens as it deepens. Area of skin contact is small.
angles relative to the canthomeatal li ne as diagrammed in figure 5. These cuts were designed to be parall el to th e sonographic beam and show the same anatomy as th e clinical sonog rams in figures 7 A, SA, 9A, 1 OA, and 11 A. A second brain from a simi lar infant was sli ced in fi ve sagittal planes centered on the anteri or fontanell e, as seen in figure 6. The placement of th ese cuts was designed to be parall el to the sonographic beam and show the same anatomy as figures 1 2A, 13A, and 14A.
Results and Observations
Figure 7: coronal image with th e transducer placed on the anteri or fontanell e so th at th e sonographi c beam is angled 80° relati ve to the canth omeatal line (fig. 5 , plane 1). The plane of section includes the hypoechoic slitlike frontal horns of the lateral ventricles (5) and th e fluid-filled cavum Fig . 2 .-Hand-held unit is placed in surgical glove to maintain steri li ty. of the septum pellucidum (6), which li es between the frontal Transducer head fi ts into thumb o f glove. horns and is a normal structure in preterm infants. The relatively echoic heads of the caudate nuclei (7) lie inferi or to the lateral parts of th e frontal horns. Also well seen are are record ed at the level of the anteri or part of the frontal horns, the the bony landmarks, which inc lude the anterior clinoids (1 0) caudate nu clei in th e pl ane of the middle cerebral arteries, the th ird and the floor of the middle cranial fossa (12). The paren ventricle, the midbody of th e thalamus, and the atria of the lateral c hyma of the temporal lobes (11) and frontal lobes (3) has ventricles in the region of th e c horoid plexus. The transducer is th en turned 90° into the sagittal plane and rocked in a similar a low echogenicity relative to the caudate nuclei. Specific fashion (figs. 4 and 6). Sagittal freeze-frame images are recorded gyri such as the gyrus rectus (8) and c ingulate gyrus (1) at the midli ne as well as at the level of both caudate nuc lei and the can be identified by the echogenic subarachnoid c isterns lateral parts of both lateral ventricles. th at outline their boundaries. Vascular anatomy demon Anatomic-pathologic correlati on with sonograms was obtained strated includes the pericallosal artery (2) and the middle by cutting two neonatal brains in pl anes parall el to the pl anes of th e cerebral arteries (9) in the sylvian fissure (13). These arterial sonographic images generated through th e anteri or fontanelle. Th e structures are identified by their pulsations as well as their first brain specimen was from a term infant whose death 1 week location. aft er deli very was attributed to sudden infant death syndrome. At Figure 8: coronal secti on 70° to th e canthomeatal line autopsy the locati on of the anteri or fontanell e was marked on the (fig. 5 , pl ane 2) with th e transd ucer on th e anteri or fontanell e superi or su rface of th e brain . Tile brain was then removed from the skull and scanned in a water bath to in sure that it was sonographi angled 10° posteri or to fi gure 7 A. This secti on in c ludes the call y normal. Next, the brain was sliced five times in the coronal lateral ventricles (5), the foramina of Monro (1 4), the th ird plane with the superior part of each slice beginning just below the ventricle (15), and the parahippocampal gyrus (16). The anterior fontanelle. The slices extended inferiorly in five different bony landmarks of the greater wing of the sphenoid (17) AJNR:2, July / August 1981 SECTOR SCANNING OF NEONATAL CRANIUM 351
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4 5 6 Fi g. 4 .- lmaging is centered on anterior fontanell e in both coronal and Fig. 6 .- Transducer is turned 90° and rocked on th e anteri or fontanell e sagittal planes. so that angled sag ittal im ages may be recorded of midline and two lateral Fig . 5.- Transducer is rocked on anteri or fontanell e so that angled coronal levels on eac h side; neonatal cadaver brai n was sli ced in these sa me planes im ages may be recorded at five different levels; neonatal cadaver brain was (see figs. 12-1 4). sliced in these same planes (see figs. 7 -11 ).
and the floor of the middle cranial fossa (12) are dense of this section inc ludes the lateral ventri cles (5), th e thala bands of linear echoes defining the inferior extent of th e mus (22), th e quadrigeminal cistern (23), and the cerebell ar cranium. The homogenous low echogeni c brain paren vermi s (24). The lateral ventricles are again slitlike with th e chyma of the temporal lobe (11) is again defined with the echoic caudate nuclei (7) in a similar inferolateral position cingulate gyrus (1) and parahippocampal gyrus (16) relati ve to th e ventricles. The large hypoechoic th alami (22) bounded by the hyperechoic subarachnoid cisterns. The are inferi or to th e ve ntricles and are separated dorsocau peri callosal artery (2) is seen in the midline pulsating supe dall y by the echoic quadrigeminal cistern (23). The parahi p rior to the hypoechoic corpus callosum (4). The corpus pocampal gyru s (16) borders the inferolateral margin s of callosum is a homogenous hypoechoic bridge of tissue just th e quadrigeminal c istern . The hi ghl y echogenic vermis of superior to the medial parts of the lateral ventricles. The th e cerebellum (24) is the most inferi or structure. The slop lateral ventricles (5) are arcuate and slitli ke with the foramina ing tentorial margin s (2 1) outline th e superi or aspect of the of Monro (14) extending from their inferior medial margins. cerebellum, with th e pari etal bone identified laterall y (25). The fluid-filled hypoechoic cavum of the septum pellucidum Figure 11 : coronal section 40° to th e canthomeatal line (6) lies between the lateral ventricles and must be distin (fig. 5, pl ane 5) with the transducer on th e anteri or fontanell e guished from the more inferiorly placed third ventricle (1 5). angled 10° posterior to fi gure 10A. This pl ane of secti on Adjacent to the inferolateral margins of the lateral ventrioles includes th e atria of th e lateral ventric les (5), th e spl enium are the bodies of the caudate nuclei (7). of the corpus call osum (27), and th e vermi s of th e cerebel Figure 9: coronal section 60° to the canthomeatal line lum (24). The pulsating peri call osal artery (2) continues in (fig. 5 , plane 3) with the transducer on the anterior fontanelle the midline between th e superi or margins of th e ve ntricles. angled 10° posterior to figure SA . This plane includes the The pulsatil e highly echogeni c c horoid pl exus (26) can be lateral ventricles (5), the body of the caudate nucleus (7), seen lying along th e inferomedial portion of th e atri a of th e the thalamus (22), the cerebral peduncles (19), and th e lateral ventric les. The larg e hypoechoic structure separating upper extent of the pons (20). The ventricles continue to be the lateral ventric les is the spl enium of th e corpus coll osum arcuate and slitlike with the pericall osal artery (2) pulsating (27). The posteri or part of the sylvian fi ssure (1 3) is seen as just superior to the hypoechoic corpus callosum (4). The a horizontal band of linear echoes lateral to the ve ntricles. body of the caudate nucleus (7) is again noted to be more echogenic than the surrounding white matter. The th alami Sagittal Sections (22) are large bilateral medium echo level structures inferior, medial, and posterior to the caudate nuclei. The cerebral Figure 12: midline sagittal pl ane with th e transducer cen peduncles (19) extend inferiorly in V-shaped hypoechoic tered on the anterior fontanell e (fig . 6, pl ane 1). Thi s section bands that fuse at the pons (20), an equally hypoechoic includes th e pulsatil e call osal marginal (2S) and peri call osal structure. Bright specular echoes lateral to the pons repre arteri es (2) whic h are immediately superi or to th e large flui d sent the edges of the tentorium (21) and the c horoidal filled cavum septum pellucidum and cavum vergae (35). fissure (34). Inferior to th e cava is th e fluid-filled anechoic third ve ntricle Figure 10: coronal section 50° to the canthomeatal line (15). Extending from th e posteri or inferi or margin of th e (fig. 5 , plane 4) with the transducer centered on the anterior third ventric le is th e cerebral aqueduct (29) which traverses fontanelle and angled 10° posterior to figure 9A. The pl ane inferiorly over the hypoechoic midbrai n (1 S). The pons (20) 352 SHUMAN ET AL. AJNR:2, July/ August 1981
A 8 Fig . 7.-Coronal secti on 80° to canthomeatalline is descri bed in text under Results and Observations.
Fig. 8. -Coronal secti on 70 ° to canthomeatal line is described in text under Results and Observations. AJN R:2. July/ August 1981 SECTOR SCANNIN G OF NEONATAL CRANIUM 353
A B Fig. 9.- Coronal secti on 60° to canthomeatal line is descri bed in text under Results and Observations.
Fi g. 1 O. - Coronal section 50.0 to cant hom eata I line is descri bed in text under Results and Observations. 3 54 SHUMAN ET AL. AJNR:2, July/ August 1981
A B Fig. 11 .- Coronal section 40 0 to canthomeatalline is described in text under Results and Observations.
Fig . 12.-Midline sagittal secti on centered on anteri or fontanelle is described in text under Results and Observations.
and the medulla (30) are continuous with the midbrain and the junction line between them, the thalamocaudate notch are of equally low echogenic ity. Posterior to the pons is the (32) can be identified. The inferior bony margins are formed very echogenic vermis of th e cerebellum (24). The specular by the floor of the anterior fossa (33) and the occipital bone occipital bone (31) forms the inferior margin of the posterior (31 ). fossa. Figure 14: sagittal plane with the transducer on the an Figure 13 : sagittal pl ane with th e transducer centered on terior fontanelle angled 20° lateral to the midline (fig. 6, th e anteri or fontanell e and angled 10° lateral to the midline plane 3). This pl ane of section includes the fluid-filled atrium, (fig . 6, plane 2). The atrium of th e lateral ventricle (5) is filled occipital horn, and temporal horn of the lateral ventricles (5, with th e pulsatil e, highly echogenic choroid pl exus (26). The 3 6 , 37, respectively). The highly echoic choroid plexus (26) large hypoechoic thalamus (22) is inferi or to the convexity can be seen running along the floor of the atrium into the of the lateral ventricle, with the more echoic caudate nuc leus temporal horn. Encased by the sweep of the ventricle is the (7) lying just anteri or to th e th alamus. At the superior part of lateral part of the th alamus (22). AJ NR :2. July / Aug ust 1981 SECTOR SCANNING OF NEONATAL CRANIUM 355
A 8 Fi g. 13. - Sagittal section 10 ° lateral to midline is described in text under Results and Observations.
A 8 Fi g. 14.- Sagittal secti on 20° lateral to midline is described in text under Results and Observations.
Discussion Numerous cranial stru ctures, in cluding ventricles, brain Sonography of the head was first performed in 1955 and stem, basal ganglia, and brain parenchyma, could be visu involved the use of A-mode to detect midline structures and ali zed. The accuracy of compound gray scale echoence obtain a crude estimation of ventricular size . Two dimen phalographic measurements has been well establi shed and sional bidirectional echoencephalography appeared in 1963 compares with th ose obtained from computed tomography and was a significant technical advance since it provided (CT) [7, 8]. Gray scale compound imaging offers several better information about ventricular size as well as intracra advantages over CT: less time required per study, lack of nial spatial relationships [2, 3]. However, only a relatively ionizing radiation, significantly lower cost, elimination of the few highly specular structures could be demonstrated. The need for sedation, and fewer artifacts . However, for both next technical improvement was the appli cation of gray CT and compound gray scale sonography, a newborn pa scale compound static scanners to echoencephalography, tient must be removed from the protective environment of which markedly improved image information content [4-6]. the NICU and the infant incubator. 356 SHUMAN ET AL. AJNR :2. July / August 1981
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