(Radiographics. 2000;20:907-922.)
© RSNA, 2000
Midface Anomalies in Children1
Lisa H. Lowe, MD,
Timothy N. Booth, MD,
Jeanne M. Joglar, MD and
Nancy K. Rollins, MD
1 From the Department of Radiology, Vanderbilt Children's Hospital, 1161 21st Ave S, D-1120 Medical Center North, Nashville, TN 37232-2675 (L.H.L.); and the Department of Radiology, Children's Medical Center of Dallas, Dallas, Tex (T.N.B., J.M.J., N.K.R.). Received April 6, 1999; revision requested June 11 and received July 21; accepted July 23. Address correspondence to L.H.L. (e-mail:lisa.lowe@mcmail.vanderbilt.edu).
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Abstract
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A variety of congenital midface anomalies occur in children. High-resolution computed tomography (CT) and magnetic resonance (MR) imaging have proved helpful in determining the nature and extent of dysplasia, thereby facilitating treatment planning. A classification system has been developed that groups these anomalies into four categories based on embryogenesis and anatomic location. These categories comprise anomalies that are related to the nasal cavity, nasofrontal region, nasolacrimal apparatus, and craniofacial syndromes. CT is the imaging modality of choice in children with possible choanal atresia, pyriform aperture stenosis, or anomalies of the nasolacrimal duct (eg, nasolacrimal duct stenosis, dacryocystoceles). MR imaging is the modality of choice in patients with congenital midface masses (eg, dermoid and epidermoid cysts, nasal gliomas, encephaloceles) and craniofacial syndromes (eg, Apert syndrome, Crouzon syndrome, Treacher Collins syndrome). In many cases, however, both CT and MR imaging are required to adequately evaluate midface anomalies. Familiarity with the characteristic imaging features of these anomalies along with knowledge of midface embryogenesis and normal developmental anatomy is essential to prevent misinterpretation of anatomic variations that may simulate disease.
Index Terms: Apert syndrome, 24.1499 • Brain, hernia, 13.1461 • Brain neoplasms, 13.363 • Crouzon syndrome, 24.1499 • Dermoid, 261.3622 • Epidermoid, 261.3622 • Face, abnormalities, 24.166, 24.1664 • Lacrimal duct and gland, 223.1492 • Nose, abnormalities, 261.1492, 261.1493, 261.361 • Treacher Collins syndrome, 24.1664
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LEARNING OBJECTIVES FOR TEST 1
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After reading this article and taking the test, the reader will be able to:
- Explain the influence of median facial embryogenesis on normal and abnormal midface development and anatomy.
- Recognize normal developmental anomalies of the midface that may simulate disease.
- Identify and describe the key CT and MR imaging features of a variety of pathologic conditions that involve the midface in children.
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Introduction
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Recent progress in surgical therapy for congenital midface anomalies has led to the use of high-resolution computed tomography (CT) and magnetic resonance (MR) imaging to help determine the extent of disease and plan appropriate management. Familiarity with midface embryogenesis allows an understanding of the pathophysiologic basis of midface anomalies as well as characteristic imaging features and associated anomalies. An understanding of normal developmental anatomy is required to prevent misinterpretation of anatomic variations that may simulate disease.
In this article, we discuss various congenital midface anomalies related to the nasal cavity, nasofrontal region, and nasolacrimal apparatus and to craniofacial syndromes with emphasis on embryogenesis, developmental anatomy, developmental variations that may simulate disease, and characteristic imaging features. We also discuss various CT and MR imaging approaches and techniques for the evaluation of these mid-face anomalies, which include choanal atresia and stenosis, pyriform aperture stenosis, dermoid and epidermoid cysts, dermal sinus tracts, nasal gliomas, encephaloceles, nasolacrimal duct stenosis, dacryocystoceles, dacryocystitis, Apert syndrome, Crouzon syndrome, and Treacher Collins syndrome.
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Midface Embryogenesis
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Midface and Nasal Cavity
The midface, or area between the upper lip and forehead, develops between 4 and 8 weeks of postovulatory age (Fig 1) (1,2). The frontal prominence forms during the 4th postovulatory week and gives rise to the superior and middle portions of the face (3). The maxillary and nasal swellings form beneath the frontal prominence. Surface thickening of the nasal swellings forms the nasal placodes. The placodes invaginate, producing the nasal pits that become the anterior choanae (nostrils) and, less superficially, the primitive posterior choanae. Epithelial plugs initially fill the primitive posterior choanae and are resorbed to form the permanent posterior choanae during the third trimester. The medial nasal and frontal processes give rise to the nasal septum, frontal bones, nasal bones, ethmoid sinus complexes, and upper incisors. The lateral nasal and maxillary processes fuse to form the philtrum and columella (ie, the septal cartilage at the tip of the nose) (3). The cartilaginous nasal capsule forms deep to the nasal and frontal bones from the chondrocranium (skull base) during the 7th and 8th postovulatory weeks (4,5).
Nasofrontal Region
The nasofrontal fontanelle, or fonticulus frontalis, temporarily separates the embryonic nasal and frontal bones. Simultaneously, the transient prenasal space separates the nasal bones and the cartilaginous nasal capsule (3,4,6,7). A diverticulum of dura mater extends from the anterior cranial fossa through the foramen cecum into the transient prenasal space. It briefly contacts the skin at the tip of the nose before retracting back into the cranium. The tract of the dural diverticulum quickly involutes. The nasal and frontal bones fuse, obliterating the fonticulus frontalis and forming the nasofrontal suture. The prenasal space becomes smaller with growth of the adjacent bone structures, eventually being reduced to a small canal anterior to the crista galli known as the foramen cecum. Finally, the foramen cecum is filled with fibrous tissue and fuses with the prenasal space (Fig 2) (1,5).
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Figure 2. Normal embryologic development of the nasofrontal region. (a) Schematic illustrates the temporary fonticulus nasofrontalis and prenasal space. (b) Schematic illustrates how the fonticulus frontalis closes, the foramen cecum is formed, and a projection of dural diverticulum contacts the tip of the nose. (c) Schematic illustrates how the dural diverticulum retracts into the cranium and the prenasal space is obliterated. (Reprinted, with permission, from reference 5.)
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Nasolacrimal Apparatus
At 30 days of postovulatory age, the nasolacrimal apparatus begins to form along the naso-optic groove, and around the 40th day, surface ectoderm is buried in the underlying mesenchyma, forming an epithelial cord (Fig 1) (8). This cord is canalized from the 3rd to 7th in utero months (9,10). The lacrimal sac forms at the cephalic end of this cord in the medial canthus. The nasolacrimal duct forms along the caudal portion of the naso-optic groove and opens below the middle turbinate bone via the Hasner membrane. Spontaneous rupture of the Hasner membrane to form a mucosal fold known as the Hasner valve usually occurs during the 1st year of life. The Hasner membrane is imperforate in up to 6% of live births and 73% of stillborn births (8–10), a discrepancy that may provide a clue to the normal mechanism of membrane perforation. Many investigators believe that initial crying or attempts to breathe as well as movement or tear production are required for membrane perforation (9,10).
Craniofacial Syndromes
The causes and embryogenesis of craniofacial syndromes are not well understood. Although many of these syndromes are congenital, most occur sporadically. They are thought to result from inadequate migration and formation of facial mesenchyma and the skull base (11). A large number of associated brain anomalies are seen in craniofacial syndromes, although the specific reason for this is also unknown.
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Midface Anatomy
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Nasal Cavity
The pyriform aperture, a pear-shaped, bony inlet of the nose, is formed by the nasal and maxillary bones. The maxillary spines mark the inferior margin of the pyriform aperture (Fig 3). The posterior choanae, or openings between the nasal cavity and the nasopharynx, should measure at least 0.34 cm in adults but should not exceed this width in children under 2 years of age (1). The posteroinferior vomer normally measures less than 0.23 cm in width and should not exceed 0.55 cm in children under 8 years of age (1). The nasal septum is composed of the vomer, the septal cartilage, and the perpendicular plate of the ethmoid bone. A focal bulge of the anterior nasal septum known as the septal tubercle or septal tumescence is normally seen at the level of the middle turbinate bone and should not be mistaken for enlargement due to a mass or sinus tract (Figs 4, 5) (5).
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Figure 3. Normal nasal cavity anatomy in a 28-month-old girl. Axial CT scan demonstrates the pyriform aperture (pa), posterior choanae (pc), and vomer (V). The maxillary spines (ms) mark the inferior margin of the pyriform aperture.
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Figure 5a. Normal anatomy of the nasofrontal region in a 3-month-old boy. (a) Axial CT scan shows the nasolacrimal duct (nl), pituitary canal (pit), and a normal cleft between the paired nasal bones (arrow). (b) Coronal CT scan demonstrates the nonossified crista galli (cg), the cribriform plate (cp), and the perpendicular plate of the ethmoid bone (pe). A focal bulge in the nasal septum, the septal tumescence (*), should not be mistaken for a mass.
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Figure 5b. Normal anatomy of the nasofrontal region in a 3-month-old boy. (a) Axial CT scan shows the nasolacrimal duct (nl), pituitary canal (pit), and a normal cleft between the paired nasal bones (arrow). (b) Coronal CT scan demonstrates the nonossified crista galli (cg), the cribriform plate (cp), and the perpendicular plate of the ethmoid bone (pe). A focal bulge in the nasal septum, the septal tumescence (*), should not be mistaken for a mass.
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Nasofrontal Region
The nasal bridge, or glabella, is superficial to the nasal and frontal bones. A midline separation between the paired nasal bones is normally seen and should not be mistaken for a dermal sinus tract. The cribriform plate separates the nasal cavity from the anterior cranial vault. Nonossification of the cribriform plate is normal in neonates and may simulate a connection between the anterior cranial fossa and the nasal cavity (Fig 5). The foramen cecum, located between the frontal bone and the crista galli, measures up to 10 mm in width (average, 4 mm) (5). It contains fibrous tissue and has soft-tissue attenuation at CT and low to intermediate signal intensity at MR imaging. The crista galli forms the cephalic portion of the cribriform plate and measures 1–8 mm in width (average, 3 mm) (5). It has a CT attenuation and MR imaging signal intensity similar to those of bone marrow. Ossification of the crista galli occurs at approximately 1 year of age, with fatty replacement occurring in most children by age 5 years and in all children by age 14 years (Fig 6). Fatty change within the crista galli should not be confused with a dermoid cyst (Fig 7).
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Figure 6. Normal anatomy of the nasofrontal region in a 10-year-old boy. Coronal CT scan demonstrates the ossified crista galli (cg), the cribriform plate (cp), and the perpendicular plate of the ethmoid bone (pe).
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Figure 7. Normal anatomy of the nasofrontal region in a 15-year-old boy. Coronal T1-weighted MR image shows bright signal intensity in the crista galli (cg) due to fatty replacement, a finding that should not be mistaken for a dermoid cyst.
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Nasolacrimal Apparatus
Tears drain through the superior and inferior canaliculi, into the common canaliculus, through the valve of Rosenmuller and into the lacrimal sac and nasolacrimal duct (Fig 8). The nasolacrimal duct drains into the inferior meatus of the nasal cavity via the Hasner valve, which prevents retrograde flow of nasal secretions during increased intranasal pressure (7,9,10).
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Figure 8. Normal nasolacrimal drainage system. Schematic illustrates the drainage of nasolacrimal secretions from the orbit into the nasal cavity. (Reprinted, with permission, from reference 10.)
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Imaging Approaches and Techniques
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CT is the imaging modality of choice in children with possible pyriform aperture stenosis, choanal atresia, or anomalies of the nasolacrimal duct. MR imaging is the modality of choice for initial evaluation of lesions with potential intracranial extension or associated intracranial anomalies such as congenital midface masses. Both CT and MR imaging are often required to adequately evaluate the bone, brain, and soft-tissue components of midface anomalies, especially congenital masses and craniofacial syndromes (3).
Axial and coronal high-resolution CT scans are obtained through the midface in planes parallel and perpendicular to the hard palate. Coronal images, although more difficult to obtain in sedated children and infants, are often more easily obtained with the patient prone. If a child cannot be positioned for prone imaging, image reformatting is a valid option. Sagittal reformatted images may also be useful in selected cases but are produced less frequently. Images are obtained with a bone algorithm at a section thickness and interval of 3 mm or less. Contrast material is administered intravenously in cases of possible infection, and images are reconstructed to a small field of view appropriate to the size of the patient. Three-dimensional CT scans of the midface bone structures may be used to elucidate the findings. Although three-dimensional images usually provide little information that is not already available on the two-dimensional images, they can provide the surgeon with a quick, easy-to-understand overview of the bone structures.
Axial and coronal T1-weighted spin-echo MR images are obtained in planes similar to those used in CT. Sagittal T1-weighted spin-echo MR images are also obtained. MR imaging is performed with a section thickness of 3 mm, a matrix of 256 x 192 or greater, a 0.5-mm gap between sections, a field of view of 16 cm or less, and four signals acquired. High-resolution T2-weighted fast spin-echo imaging is performed with the same parameters except a matrix of 256 x 256 or greater. Contrast material–enhanced fat-suppressed T1-weighted MR images may be obtained in cases of possible infection or neoplasm.
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Classification of Pediatric Midface Anomalies
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Midface anomalies are often classified according to the presence of airway obstruction at clinical examination (12). Anomalies with bilateral airway obstruction usually manifest during the neonatal period and require urgent imaging and therapy, whereas those with unilateral airway obstruction generally manifest later in life. This classification system is useful in determining the clinical significance of an anomaly but is less applicable radiologically because any of these anomalies has the potential to cause airway obstruction depending on its size and location. We use a classification system based on the embryology and anatomy of the nasal cavity, nasofrontal region, and nasolacrimal apparatus as well as anomalies associated with craniofacial syndromes.
Nasal Cavity
Choanal Atresia and Stenosis.—Choanal atresia is the most common cause of neonatal nasal obstruction and occurs in one of every 5,000–8,000 neonates (1,12). Bilateral choanal atresia, more commonly than unilateral atresia, usually causes respiratory distress that is relieved by crying in neonates who are obligate nose breathers for the first 2–6 months of life (7,8). Bilateral obstruction is life-threatening and requires immediate measures to ensure an adequate airway. Unilateral choanal atresia may go unrecognized until later in life when there is nasal stuffiness, rhinorrhea, or infection. Choanal atresia is classified as osseous (90% of cases), membranous (10%), or, occasionally, osseomembranous (3,13). Osseous obstruction is due to incomplete canalization of the choanae, whereas membranous obstruction is due to incomplete resorption of epithelial plugs. Choanal atresia is more common in girls and is unilateral in 50%–60% of cases (1,12). In the clinical setting, advancement of a nasal catheter to 32 mm or more excludes the diagnosis of choanal atresia (12,13). CT is the imaging modality of choice and should be immediately preceded by vigorous suctioning and administration of topical decongestants (vasoconstrictors). Patients are scanned in the prone position with the gantry angled 5°–10° cephalad to the hard palate. Images are obtained with a section thickness and interval of 1–1.5 mm and are reconstructed with a bone algorithm. Key imaging features include narrowing of the posterior choanae to a width of less than 0.34 cm in children under 2 years old, inward bowing of the posterior maxilla, fusion or thickening of the vomer, and the presence of a bone or soft-tissue septum extending across the posterior choanae (Fig 9) (1). Choanal atresia may be seen in many syndromes (Table 1), and associated systemic anomalies occur in up to 75% of patients (1,3). Choanal stenosis may appear similar to choanal atresia depending on the degree of narrowing. Choanal stenosis is diagnosed with CT and is usually treated conservatively, which allows time for normal growth of the nasal cavity. In children with unilateral obstruction, treatment can be delayed to age 6–9 years, by which time the midface has reached 90% of its adult size. In neonates with bilateral obstruction, treatment begins with securing an airway. Treatment of choanal atresia ranges from endoscopic perforation of thin membranes to choanal reconstruction and involves stent placement in osseous obstruction (1,3,12).
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Figure 9. Osseomembranous choanal atresia in a 7-month-old girl with chronic rhinorrhea. Axial CT scan shows inward bowing of the maxilla, bone stenosis of the right posterior choanae (arrowheads), and a membrane occluding the choanal lumen (arrow). The vomer is normal in thickness.
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Pyriform Aperture Stenosis.—Pyriform aperture stenosis results from early fusion and hypertrophy of the medial nasal processes. Pyriform aperture stenosis is a rare cause of airway obstruction, and its prevalence is unknown. Many anomalies are associated with this disease entity, including alobar and semilobar forms of holoprosencephaly, facial hemangiomas, clinodactyly, pituitary dysfunction, and, in 75% of cases, a central megaincisor (1,3). High-resolution CT is the imaging modality of choice. It is performed in planes angled along the hard palate with a section thickness of 1–1.5 mm and should include the maxillary spines. Imaging features of pyriform aperture stenosis include a shelf of tissue extending across the nostrils just inside the nares, inward bowing of the maxillary spines, and narrowing of the pyriform aperture (Fig 10). No standard measurements exist for the normal pyriform aperture; consequently, the diagnosis of aperture stenosis may be difficult. Associated intracranial anomalies can be excluded in infants with MR imaging or ultrasonography. Treatment of mild cases of pyriform aperture stenosis includes administration of decongestants, which allows time for normal nasal growth. Severe cases may require surgical reconstruction with stent placement, sublabial resection of the anteromedial maxilla, or reconstruction of the anterior nasal passages (1,3,12).
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Figure 10. Pyriform aperture stenosis in a 2-day-old boy with respiratory distress. Axial CT scan reveals inward bowing of the maxillary spines (arrow) and narrowing of the pyriform aperture (pa).
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Nasofrontal Region
Congenital midline nasofrontal masses are the result of faulty regression of the embryologic dural diverticulum from the prenasal space and occur in one of every 20,000–40,000 births. The type of mass is determined by the nature of the faulty regression (Fig 11). The mass may be intranasal, extranasal, or a combination of the two. Intranasal masses are due to extension of dura mater through the foramen cecum into the prenasal space and nasal cavity. Glabellar masses are due to extension of the diverticulum through the foramen cecum and fonticulus frontalis. Congenital midline masses are often obvious at birth but can manifest at any age (4). Midface disfigurement, nasal destruction, meningitis, and airway obstruction may occur. Imaging helps characterize these lesions so that the surgical approach can be planned as extracranial, intracranial, or both. Findings that suggest intracranial extension include widening of the foramen cecum and a bifid or dystrophic crista galli (6). Nasofrontal masses most commonly manifest as dermoid or epidermoid cysts, nasal gliomas (nasal cerebral heterotopias), or encephaloceles (Table 2) (1,5).
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Figure 11a. Faulty development of the nasofrontal region leading to formation of various midface masses. (a) Schematic illustrates how dermal sinus tracts form when there is no involution or only partial involution of the dural diverticulum that extends through the foramen cecum to the columella. Dermoid and epidermoid cysts may form anywhere along the course of the dermal sinus tract owing to desquamation of tissue lining the tract. (b) Schematic illustrates how nasal gliomas form when the dural diverticulum that extends through the foramen cecum does not retract and involute normally, leaving sequestered neurogenic tissue that may be connected to the intracranial contents by a fibrous stalk. (c) Schematic illustrates how frontonasal encephaloceles form when the fonticulus nasofrontalis remains patent. (d) Schematic illustrates how nasoethmoidal encephaloceles form when the foramen cecum fails to close and the prenasal space remains patent. (Reprinted, with permission, from reference 5.)
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Figure 11b. Faulty development of the nasofrontal region leading to formation of various midface masses. (a) Schematic illustrates how dermal sinus tracts form when there is no involution or only partial involution of the dural diverticulum that extends through the foramen cecum to the columella. Dermoid and epidermoid cysts may form anywhere along the course of the dermal sinus tract owing to desquamation of tissue lining the tract. (b) Schematic illustrates how nasal gliomas form when the dural diverticulum that extends through the foramen cecum does not retract and involute normally, leaving sequestered neurogenic tissue that may be connected to the intracranial contents by a fibrous stalk. (c) Schematic illustrates how frontonasal encephaloceles form when the fonticulus nasofrontalis remains patent. (d) Schematic illustrates how nasoethmoidal encephaloceles form when the foramen cecum fails to close and the prenasal space remains patent. (Reprinted, with permission, from reference 5.)
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Figure 11c. Faulty development of the nasofrontal region leading to formation of various midface masses. (a) Schematic illustrates how dermal sinus tracts form when there is no involution or only partial involution of the dural diverticulum that extends through the foramen cecum to the columella. Dermoid and epidermoid cysts may form anywhere along the course of the dermal sinus tract owing to desquamation of tissue lining the tract. (b) Schematic illustrates how nasal gliomas form when the dural diverticulum that extends through the foramen cecum does not retract and involute normally, leaving sequestered neurogenic tissue that may be connected to the intracranial contents by a fibrous stalk. (c) Schematic illustrates how frontonasal encephaloceles form when the fonticulus nasofrontalis remains patent. (d) Schematic illustrates how nasoethmoidal encephaloceles form when the foramen cecum fails to close and the prenasal space remains patent. (Reprinted, with permission, from reference 5.)
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Figure 11d. Faulty development of the nasofrontal region leading to formation of various midface masses. (a) Schematic illustrates how dermal sinus tracts form when there is no involution or only partial involution of the dural diverticulum that extends through the foramen cecum to the columella. Dermoid and epidermoid cysts may form anywhere along the course of the dermal sinus tract owing to desquamation of tissue lining the tract. (b) Schematic illustrates how nasal gliomas form when the dural diverticulum that extends through the foramen cecum does not retract and involute normally, leaving sequestered neurogenic tissue that may be connected to the intracranial contents by a fibrous stalk. (c) Schematic illustrates how frontonasal encephaloceles form when the fonticulus nasofrontalis remains patent. (d) Schematic illustrates how nasoethmoidal encephaloceles form when the foramen cecum fails to close and the prenasal space remains patent. (Reprinted, with permission, from reference 5.)
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Dermoid and Epidermoid Cysts.—Dermoid and epidermoid cysts occur when skin elements are pulled into the prenasal space along with the regressing dural diverticulum. A sinus tract or mass, each of which is seen in 50% of cases, may form anywhere along the course of the diverticulum from the columella to the anterior cranial fossa (1,4). An intracranial connection is seen in up to 57% of affected patients (3). Dermoid cysts contain ectoderm with skin appendages, are slightly more common than epidermoid cysts, and are usually midline with a tendency to occur at the glabella. Epidermoid cysts contain ectodermal elements without skin appendages, are usually paramidline, and tend to occur near the columella (1,3,7). A sinus tract opening, dimple, or tuft of hair is present on the skin surface in up to 84% of dermoid or epidermoid cysts and dermal sinus tracts (5). Dermoid and epidermoid cysts are firm, nonpulsatile lesions that do not transilluminate and do not change in size with crying or with compression of the jugular veins (negative Furstenberg test) (6). The imaging characteristics of dermoid and epidermoid cysts may overlap, although dermoid cysts are more likely to be midline and fatty, whereas epidermoid cysts usually have fluid attenuation at CT and are isointense relative to fluid at T1- and T2-weighted MR imaging (Figs 12, 13). Although extracranial epidermoid cysts rarely present a diagnostic dilemma, intracranial lesions may mimic arachnoid cysts. Intracranial arachnoid cysts are solid masses that can be identified at MR imaging with diffusion-weighted or magnetization transfer sequences. On diffusion-weighted images, epidermoid cysts have characteristics of solid tissue, appearing similar to brain. Magnetization transfer sequences demonstrate significant transfer of magnetization from the solid epidermoid cyst matrix to adjacent free water; this transfer is not seen in fluid-containing lesions. Imaging helps determine whether there is intracranial extension and is therefore important in planning the surgical approach. Treatment of dermoid and epidermoid cysts includes complete resection of the mass and, if present, the sinus tract (1,4). Incomplete resection may lead to complications of meningitis or recurrence in up to 15% of cases (6). With intracranial involvement, intracranial-extracranial resection is required to remove the mass and its sinus tract (7). Resection of the mass may be delayed until 2–5 years of age if possible.
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Figure 12. Dermoid cyst in a 2-year-old girl with a midline nasal mass. Axial CT scan reveals a midline fatty mass (arrows) with nasal bone erosion. The mass, characteristically located at the glabella, is not connected to the foramen cecum (arrowheads).
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Figure 13a. Dermoid cyst with a dermal sinus tract in a 16-month-old girl with a midline nasal dimple. (a) Sagittal T1-weighted MR image obtained with a vitamin E tablet placed over the midline dimple (E) shows soft-tissue signal intensity within the fat of the glabella (black arrows) and high signal intensity within the crista galli (white arrow), findings that are worrisome for intracranial extension. (b, c) Axial (b) and coronal (c) fat-suppressed T2-weighted MR images show bright signal intensity within the soft tissue of the glabella (solid arrow in b) and the foramen cecum (open arrow). These findings are consistent with a glabellar dermoid cyst accompanied by a dermal sinus tract extending through the foramen cecum.
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Figure 13b. Dermoid cyst with a dermal sinus tract in a 16-month-old girl with a midline nasal dimple. (a) Sagittal T1-weighted MR image obtained with a vitamin E tablet placed over the midline dimple (E) shows soft-tissue signal intensity within the fat of the glabella (black arrows) and high signal intensity within the crista galli (white arrow), findings that are worrisome for intracranial extension. (b, c) Axial (b) and coronal (c) fat-suppressed T2-weighted MR images show bright signal intensity within the soft tissue of the glabella (solid arrow in b) and the foramen cecum (open arrow). These findings are consistent with a glabellar dermoid cyst accompanied by a dermal sinus tract extending through the foramen cecum.
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Figure 13c. Dermoid cyst with a dermal sinus tract in a 16-month-old girl with a midline nasal dimple. (a) Sagittal T1-weighted MR image obtained with a vitamin E tablet placed over the midline dimple (E) shows soft-tissue signal intensity within the fat of the glabella (black arrows) and high signal intensity within the crista galli (white arrow), findings that are worrisome for intracranial extension. (b, c) Axial (b) and coronal (c) fat-suppressed T2-weighted MR images show bright signal intensity within the soft tissue of the glabella (solid arrow in b) and the foramen cecum (open arrow). These findings are consistent with a glabellar dermoid cyst accompanied by a dermal sinus tract extending through the foramen cecum.
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Nasal Gliomas.—Nasal gliomas (nasal cerebral heterotopias) are rare developmental masses composed of dysplastic, sequestered, neurogenic tissue that has become isolated from the subarachnoid space during dural diverticulum regression. The term nasal glioma is actually a misnomer because these masses have no neoplastic features (1). Nasal gliomas may be intranasal (30% of cases), extranasal (60%), or a combination of the two (10%) (3,8). Other, very rare locations of heterotopic brain include the lip, tongue, scalp, nasopharynx, and oropharynx (4). Nasal gliomas do not change in size with crying, although intranasal gliomas may grow at a rate that parallels the rate of brain growth (6,14). They are more often right-sided and unilateral and are attached to the brain by a stalk in 10%–30% of cases (5,7,12). Most nasal gliomas are identified at birth, although they have been detected as late as the 7th decade of life (14,15). At clinical examination, the intranasal type is attached high on the lateral nasal wall to the middle turbinate bone or, less often, to the nasal septum. Intranasal gliomas are soft, pale, gray or purple, polypoid, unencapsulated masses sequestered between the nasal bones and the nasal capsule. Extranasal gliomas are smooth, firm, non-pulsatile, skin-covered masses that are usually found at the glabella and may have overlying telangectatic skin. Broadening of the nasal bridge or hypertelorism may occur (4,6). Imaging features include a nonenhancing soft-tissue mass of the glabella or nasal cavity (Fig 14). At MR imaging, nasal gliomas are isointense to hypointense relative to gray matter with T1-weighted sequences and hyperintense with proton-density-weighted and T2-weighted sequences and may demonstrate an intracranial connection. Treatment and definitive diagnosis require complete excision of the mass.
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Figure 14a. Nasal glioma in a 6-month-old boy with a glabellar skin tag. Axial CT scans show a nonenhancing soft-tissue mass involving the right nasal cavity (arrows in a) and glabella (arrow in b).
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Figure 14b. Nasal glioma in a 6-month-old boy with a glabellar skin tag. Axial CT scans show a nonenhancing soft-tissue mass involving the right nasal cavity (arrows in a) and glabella (arrow in b).
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Encephaloceles.—Encephaloceles result from herniation of intracranial contents through a defect in the skull with a persistent connection to the subarachnoid space (15). They occur in one of every 4,000 live births and have no sex predilection (6). The nomenclature used for encephaloceles is based on the origin of their roof and floor (5); thus, for example, the roof and floor of frontonasal encephaloceles are the frontal and nasal bones, respectively. Encephaloceles are also classified according to location as either occipital (75% of cases), sincipital (15%), or basal (10%) (4). Sincipital encephaloceles involve the midface and occur about the dorsum of the nose, the orbits, and the forehead. They are typically either frontonasal (40%–60% of cases) or nasoethmoidal (30%) (1,3), with the remaining 10% being a combination of the two (12). Frontonasal encephaloceles result from herniation of dura mater through both the foramen cecum and the fonticulus frontalis into the glabellar region (Fig 15). Nasoethmoidal encephaloceles occur when there is persistent herniation of the dural diverticulum through the foramen cecum into the prenasal space and nasal cavity (Fig 16). Encephaloceles have a high prevalence of associated intracranial anomalies, including intracranial cysts, callosal agenesis, interhemispheric lipomas, facial clefts, and schizencephaly (5,7). Younger siblings of affected patients are at a 6% risk for a congenital central nervous system abnormality (4). Frontonasal encephaloceles are soft, cystic, and bluish when covered by skin; when not covered, they are usually red and moist. Intranasal encephaloceles are pedunculated and extend downward from the superomedial nasal cavity. Lateral advancement of a nasal catheter may help differentiate encephaloceles from more medially located dacryocystoceles (nasolacrimal mucoceles) (8).
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Figure 15. Frontonasal encephalocele in a 5-day-old girl with a midline mass. Sagittal T1-weighted MR image shows brain parenchyma within a glabellar mass (*). Outward bowing of the inferior frontal bone (arrow) and associated absence of the corpus callosum (arrowheads) are also noted.
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Figure 16. Nasoethmoidal encephalocele in a 10-year-old boy with an intranasal mass. Coronal T1-weighted MR image demonstrates a nasal mass containing cerebrospinal fluid (open arrows) and brain parenchyma (solid arrow).
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The clinical manifestation of encephaloceles is variable and may consist of an obvious mass, nasal stuffiness, rhinorrhea, a broad nasal root, or hypertelorism. Depending on the size of the intracranial connection, encephaloceles may be pulsatile or change in size during crying, the Valsalva maneuver, or jugular compression (positive Furstenberg test) (4). Biopsy is contraindicated in encephaloceles due to the potential for cerebrospinal fluid leaks, seizures, or meningitis (6).
Imaging features of nasal encephaloceles include a soft-tissue mass that is connected to the subarachnoid space via an enlarged foramen cecum and extends to the glabella or into the nasal cavity. MR imaging is the modality of choice for the initial evaluation of encephaloceles because it can help determine the size, extent, and nature of the encephalocele contents as well as the presence of associated intracranial anomalies. Encephaloceles are isointense relative to gray matter with most MR imaging sequences but may be hyperintense with T2-weighted sequences due to gliosis. CT is useful in demonstrating bone changes that suggest intracranial extension such as a bifid or absent crista galli, cribriform plate, or frontal bone. Occasionally, encephaloceles are difficult to differentiate from nasal gliomas; in such cases, intrathecal injection of contrast material may demonstrate a subarachnoid connection in encephaloceles that is not seen in nasal gliomas. Cisternography with heavily T2-weighted thin sections may also be useful.
Encephaloceles are treated with complete surgical resection as soon as possible to prevent cerebrospinal fluid leakage, meningitis, or increase in mass size. The surgical approach initially involves addressing intracranial involvement and repairing the dura mater (5). The extracranial portion of the lesion may be resected simultaneously or at a later time. Resection of the extracranial portion does not lead to an increased risk of neurologic deficit due to the abnormal function of the herniated brain tissue (1).
Nasolacrimal Apparatus
Nasolacrimal Duct Stenosis.—Nasolacrimal duct stenosis is common in neonates and is caused by at least partial persistence of the Hasner membrane. Imaging findings may be normal or may consist of accumulation of secretions within an enlarged nasolacrimal duct (Fig 17).
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Figure 17. Nasolacrimal duct stenosis in a 4-year-old boy with right epiphora. On a coronal CT scan, the right nasolacrimal duct (arrowhead) is slightly larger than the left nasolacrimal duct (arrow) due to accumulation of secretions proximal to the stenotic Hasner valve. The left nasolacrimal duct contains air, a finding that could be interpreted as normal.
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Dacryocystoceles.—Dacryocystoceles are caused by obstruction of both the proximal and distal ends of the nasolacrimal duct. An imperforate Hasner membrane causes the distal blockage, but the cause of proximal obstruction is less clearly understood (9,10). Dacryocystoceles, although rare, are the second most common cause of neonatal nasal obstruction after choanal atresia and require prompt treatment. Dacryocystoceles may be unilateral or bilateral and have no sex predilection. They commonly manifest as a tense, blue-gray mass at the medial canthus or in the nasal cavity (1). Dacryocystoceles can cause nasal obstruction, become infected, or spontaneously rupture so that their contents drain into the nose. Postnatal infection of an intact dacryocystocele is known as dacryocystitis. CT is the imaging modality of choice and allows identification of a dacryocystocele and differentiation from other intranasal masses. Prescan preparation and technique are similar to those described for choanal atresia, although no gantry angulation is required and section thickness may be increased up to 3 mm (3). Imaging features include nasolacrimal duct dilatation and a homogeneous, well-defined, thin-walled mass with fluid attenuation involving the medial canthus or nasal cavity (Fig 18). There is often superior displacement of the inferior turbinate bone and contralateral shift of the nasal septum. Intravenous administration of contrast material may demonstrate slight enhancement of the cyst wall that is more pronounced in dacryocystitis. Adjacent soft-tissue enhancement and swelling are also common in dacryocystitis (Fig 19). Treatment of nasolacrimal stenosis is graded: Initial treatment consists of duct massage during the first few months of life; if this is unsuccessful, duct probing and, rarely, ductal intubation are performed. With conservative management, ductal stenosis will resolve spontaneously in 90% of children during the 1st year of life. Prophylactic antibiotics may be used during this period to prevent dacryocystitis and periorbital cellulitis. Dacryocystoceles require prompt treatment due to a tendency to become infected and cause subsequent damage to the nasolacrimal system (10). As with nasolacrimal stenosis, treatment of dacryocystoceles is graded and ranges from manual pressure to probing with irrigation to endoscopic resection and marsupialization in severe cases (3,8).
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Figure 18a. Dacryocystoceles in a 14-day-old boy with bilateral medial canthal swelling. Axial fat-suppressed T2-weighted MR images obtained at the level of the medial canthus (a) and inferior meatus (b) demonstrate bilateral, well-defined, thin-walled masses with fluid signal intensity that follow the expected course of the nasolacrimal ducts (arrows).
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Figure 18b. Dacryocystoceles in a 14-day-old boy with bilateral medial canthal swelling. Axial fat-suppressed T2-weighted MR images obtained at the level of the medial canthus (a) and inferior meatus (b) demonstrate bilateral, well-defined, thin-walled masses with fluid signal intensity that follow the expected course of the nasolacrimal ducts (arrows).
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Figure 19a. Dacryocystitis in a 5-week-old boy with bilateral dacryocystoceles. (a) Contrast-enhanced axial CT scan shows left-sided preseptal inflammation (solid arrows) and a left medial canthal mass (*) with a thick, enhancing wall (open arrows). (b) Contrast-enhanced axial CT scan demonstrates bilateral low-attenuation and well-defined, thin-walled nasal masses (arrows).
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Figure 19b. Dacryocystitis in a 5-week-old boy with bilateral dacryocystoceles. (a) Contrast-enhanced axial CT scan shows left-sided preseptal inflammation (solid arrows) and a left medial canthal mass (*) with a thick, enhancing wall (open arrows). (b) Contrast-enhanced axial CT scan demonstrates bilateral low-attenuation and well-defined, thin-walled nasal masses (arrows).
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Craniofacial Syndromes
Craniofacial syndromes include developmental malformations of the face and skull that are associated with central nervous system malformations. The presence of central nervous system anomalies is extremely important in these syndromes because they often affect IQ and prognosis and influence outcome. Most patients can be diagnosed on the basis of the type of anomalies involving the central nervous system and extremities and the presence of similar malformations in relatives (11). These syndromes are often evaluated with CT and MR imaging, which allow detailed anatomic description for surgical planning and detection of associated intracranial lesions. Some authors have suggested that skull base hypoplasia and venous anomalies contribute to intracranial findings such as hydrocephalus; thus, cerebrospinal fluid flow studies and MR venography may have a role in the evaluation of affected patients (11). Treatment of craniofacial syndromes consists of a multidisciplinary approach in which each organ system is addressed independently and problems are prioritized on the basis of relative urgency (16). Midfacial clefts, which are among the most common congenital craniofacial anomalies, and Goldenhar syndrome are not discussed in this article. They include a large number of midline defects that, if comprehensively reviewed, would require a separate article. Instead, three craniofacial anomalies are discussed in which imaging is instrumental in planning surgical management: Apert syndrome, Crouzon syndrome, and Treacher Collins syndrome. A more complete list of craniofacial syndromes is shown in Table 3, although this list continues to grow as more knowledge is accumulated.
Apert Syndrome.—Apert syndrome (acrocephalosyndactyly type I) is an autosomal dominant disorder with incomplete penetrance that occurs in 5.5 of every 1 million neonates (17). Despite the autosomal dominant inheritance pattern, the majority of cases are sporadic. Clinical features include craniosynostosis, hypertelorism, a retruded or hypoplastic midface with a downturned mouth, and severe, symmetric syndactyly of the hands and feet (11,17,18). In nearly all cases, the calvaria has a brachycephalic appearance due to coronal synostosis. There is also a wide midline defect (widened metopic and sagittal sutures extending from the glabella to the posterior fontanelle) that closes between ages 2 and 4 years (18). Shallow orbits with proptosis, hypertelorism, and exotropia are characteristic ocular findings (Fig 20). The central nervous system may demonstrate megalocephaly, gyral abnormalities, hypoplastic white matter, heterotopic gray matter, frontal encephalocele, corpus callosal agenesis, kleeblattschädel, cleft palate, or ventriculomegaly (16,17). Although the ventricles may be enlarged, the cause for this is not well understood, and clinically significant hydrocephalus is uncommon. It is thought that the hydrocephalus may be at least partially related to skull base hypoplasia (11). This hypoplasia may also cause cranial neuropathies due to foraminal stenosis. Obstruction of venous outflow and intrinsic anomalies in brain embryogenesis may also contribute to the development of ventriculomegaly. IQ varies and is affected by the presence of associated intracranial anomalies. However, mental retardation in Apert syndrome is commonly nonprogressive, and IQ is reported to be within the normal range in up to 50% of patients (17). Cervical spine fusion occurs in up to 71% of patients with Apert syndrome and most often involves the fifth and sixth vertebrae (17,19). The nasopharyngeal and oropharyngeal airways may be compromised by hypoplasia of the posterior choanae, thereby increasing the risk of respiratory distress, obstructive sleep apnea, cor pulmonale, and sudden death. Choanal stenosis is common in Apert syndrome, but atresia is rare. Midfacial advancement surgery is useful in the treatment of these problems and often produces dramatic results (18). Apert syndrome is associated with a high prevalence of otitis media, cleft palate, eustachian tube dysfunction or distortion, bifid uvula, and a highly arched palate. Sensorineural hearing loss is rare, but conductive hearing loss is common due to external and middle ear malformations. Syndactyly most often involves the second, third, and fourth digits (11,16,17). Genitourinary anomalies may occur in 9.6% of patients and include cryptorchidism, hydronephrosis, and, rarely, polycystic kidneys or bicornuate uterus (16,17). Various cardiovascular anomalies (10% of cases) as well as respiratory (1.5%) and gastrointestinal (1.5%) anomalies may occur (16,17).
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Figure 20a. Apert syndrome in a 5-day-old boy with proptosis and syndactyly. (a) Axial CT scan demonstrates shallow proptotic orbits (arrowheads) and gradual narrowing of the nasal cavity from front to back (arrows). (b) Axial CT scan demonstrates midface hypoplasia (arrows), narrowing of the pyriform aperture (pa), and posterior choanal stenosis (pc).
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Figure 20b. Apert syndrome in a 5-day-old boy with proptosis and syndactyly. (a) Axial CT scan demonstrates shallow proptotic orbits (arrowheads) and gradual narrowing of the nasal cavity from front to back (arrows). (b) Axial CT scan demonstrates midface hypoplasia (arrows), narrowing of the pyriform aperture (pa), and posterior choanal stenosis (pc).
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Crouzon Syndrome.—Crouzon syndrome is an autosomal dominant disorder characterized by craniosynostosis, maxillary hypoplasia, shallow orbits with proptosis, bifid uvula, or cleft palate. There are often intracranial abnormalities such as anomalous venous drainage and hydrocephalus (Fig 21) (20). Hydrocephalus is more often progressive in Crouzon syndrome than in Apert syndrome (11). Chiari I malformations have proved common in Crouzon syndrome with the increased use of MR imaging (71.4% of cases). The cause of this association is not known, but the relationship of Chiari I malformation to premature lambdoid suture synostosis has been questioned (21).
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Figure 21a. Crouzon syndrome in a 14-year-old girl. (a) Sagittal T1-weighted MR image reveals a steep clivus (arrowheads), a vertically oriented brainstem (*), and a Chiari I malformation (arrow). The signal voids in the calvaria are caused by sutures from previous cranioplasty. (b) Maximum-intensity-projection image from an MR venogram shows markedly abnormal venous drainage including absence of flow in the region of the jugular bulbs (*), multiple collateral veins (arrowheads), and hypoplastic transverse sinuses (arrows).
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Figure 21b. Crouzon syndrome in a 14-year-old girl. (a) Sagittal T1-weighted MR image reveals a steep clivus (arrowheads), a vertically oriented brainstem (*), and a Chiari I malformation (arrow). The signal voids in the calvaria are caused by sutures from previous cranioplasty. (b) Maximum-intensity-projection image from an MR venogram shows markedly abnormal venous drainage including absence of flow in the region of the jugular bulbs (*), multiple collateral veins (arrowheads), and hypoplastic transverse sinuses (arrows).
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A variety of nonobligatory, noncranial manifestations of Crouzon syndrome exist, including calcification of the stylohyoid ligament in 50% of patients over 4 years old, cervical spine abnormalities in up to 40% of patients, elbow malformations (18%), minor hand deformities (10%), visceral anomalies (7%), various musculoskeletal deformities (7%), and skin lesions (19). Stylohyoid ligament calcification is also reported in 38%–88% of cases of Apert syndrome (19). Cervical spine fusion anomalies affecting C2 to C5 are the most common vertebral deformities in Crouzon syndrome (19). Limb anomalies in Crouzon syndrome are nonspecific, whereas in Apert syndrome, a specific musculoskeletal deformity is identified. Acanthosis nigrans (hyperpigmented, hyperkeratotic lesions located on the neck and near joint flexures) has also been reported in Crouzon syndrome (19).
Treacher Collins Syndrome (Mandibulofacial Dysostosis).—Treacher Collins syndrome, an autosomal dominant disorder with variable penetrance and phenotypic expression, occurs in one of every 50,000 births. Forty percent of patients have a family history of disease, and 60% of cases occur sporadically (22). Embryologic abnormalities affect structures that originate from the second and third brachial arches (23). Treacher Collins syndrome is characterized by anomalous development of all or most of the following: eyelids (antimongoloid slanting or shortened palpebral fissures, lower lid colobomas, absent eyelashes), malar bone (small or absent zygomatic arches), maxilla (narrow or overprojected maxilla, elevated or narrow palate), mandible (hypoplasia, dental ma
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Abstract
LEARNING OBJECTIVES FOR TEST...
, 5, 6, 7, and 10 weeks of development. (Reprinted, with permission, from reference 