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Figure 1. Cervical teratoma. Axial, T1-weighted MR image of theneck without contrast in a 1-day-old neonate demonstrates a largecystic and solid neck mass replacing the right lobe of the thyroid(arrow) with intact left thyroid lobe (star).majority located in the sacrococcygeal region. A germ celltumor, teratomas are thought by some to arise from thyroidtissue and may replace the thyroid gland rather than engulf it(Figure 1)—a feature that can be useful in distinguishing themfrom other large anterior cystic neck masses.6 They can beclassified into mature and immature subtypes, though the size,location, and extent of the tumor are much more important inpredicting the prognosis. Although these tumors can bedetected as early at 15 weeks’ gestation, the majority are notdiagnosed until the late second or third trimesters, suggestingthey can also develop later in the pregnancy.7Ultrasound, including Doppler and 3D imaging, and MRIare both useful in the diagnosis and evaluation of these fetusesin whom both fetal and maternal α-fetoprotein levels may benormal. On imaging, teratomas present as large cystic andsolid masses, which often hyperextend the neck and distortthe airway and vasculature. The use of T1-weighted highresolution isotropic volume excitation and gradient recallecho planar imaging (EPI) sequences may occasionally depictfat, internal hemorrhage, or calcium though these features arenot universally present in congenital cervical teratomas.Ultrasound is useful in evaluating the vascularity of the solidportion and to depict calcifications suspected by MRI, helping to differentiate teratomas from more complex venolymphatic malformations. Ultrasound can also most readilymonitor the tumor size and look for potential complicationsof airway obstruction including polyhydramnios and hydrops.Using a combination of T2-weighted single-shot turbo spinecho and heavily T2-weighted balanced turbo field echosequences in the axial, sagittal, and coronal planes, MRI canbest define the anatomic extent and internal characteristics ofthe mass. Advanced MR imaging techniques are also beingincreasingly applied to these challenging patients. The use ofcine imaging, such as a dynamic heavily T2-weighted nongated sequence, is capable of evaluating the fetal swallowingin real time and may prove to be helpful to evaluate for tonguemovement and/or involvement and for visualization ofdynamic airway obstruction. Volumetric measurements ofthe mass, and lungs in cases of severe airway compromise,can be obtained by applying superresolution postprocessingmethods to the original 2D multiplanar T2-weighted planesand aid in treatment planning and prognosis.8Although there are no specific selection guidelines in determining which fetuses should be delivered via EXIT procedure, certain imaging features predict a higher likelihood thata fetus may benefit from secured airway control before delivery given an elevated risk for severe airway obstruction. Theradiologist should thus be very descriptive in the specific location of the mass in the neck, outlining the relationship to theairway including whether or not the mass appears to arisefrom the airway, invade into the airway, or exert significantexternal compression on/deviation of the airway, as higherscores of airway deviation are predictive of a complicatedairway at birth.9 This is facilitated with T2-weighted MRI inwhich the entire course of the airway should be followed fromthe oropharynx to the carina (Figure 2). Internal characteristics of the mass are also important, such as whether the massis cystic or solid, as solid masses tend to have a higher propensity for airway obstruction. The presence of polyhydramnios should also be noted, as it is suggestive of impaired fetalswallowing and is predictive of a complicated airway at birth.Advances in neonatal surgery including the use of EXITprocedure, surgical resection of the teratoma while on placental support, and early surgical resection at specialized tertiarycenters have improved the morbidity and mortality of thesefetuses, which unfortunately still remains poor.Vascular MalformationsLymphatic malformations (LMs) are the most commoncervical tumor with variable reported incidence of four in10,000 and one in 16,0000 births,10 with the largest proportion seen in the posterior neck.11 These lesions have beenpreviously called by many names including cystic hygromawhen occurring in the nuchal location, and lymphangioma,although LM remains the most appropriate term.12 LMs maybe either macrocystic or microcystic in nature dependingFigure 2. Cervical teratoma. Axial, T2-weighted MR image of theneck in a 32-week fetus demonstrates a cystic and solid neck mass(star), which deviates the airway ventrally and to the left (arrow).3

upon the size of the cystic spaces. They may also consist ofa mixture of venous and lymphatic components giving riseto combined lesions known as venolymphatic malformations.In the anterior neck, LMs are the main differential for a largeanterior cystic neck mass.Ultrasound is a useful first modality to document the cysticnature of these masses and exclude internal vascularity apartfrom within the internal septations, helping to differentiatethe more common subtypes of purely lymphatic and cysticvenolymphatic malformations from teratomas. The morecomplex venolymphatic malformations, which contain variable amounts of solid components and calcified phleboliths,remain a diagnostic challenge, as they can appear very similar to teratomas on prenatal imaging.13,14 LMs have the propensity to undergo internal cyst hemorrhage leading tocharacteristic fluid-blood levels. Similar to teratomas, MRIis useful to evaluate these lesions to document the positionof the airway and assess for deep neck extension of thesetransspatial lesions. LMs typically cause less mass effectcompared with similarly sized teratomas leading to lesshyperextension of the neck and less deviation and compression of the airway, vascular structures, and thyroid gland(Figure 3). They may also insinuate into the chest, mediastinum and axilla, a feature more commonly seen with venousLMs and LMs than cervical teratomas. LMs may grow,regress, or remain stable during the gestation and thus serialfollow-up is advised. Prenatal aspiration of cyst fluid can beconsidered in cases of rapid growth, infection, or hemorrhageto facilitate delivery but is rarely performed.10 Lesion airwayinvolvement necessitates similar considerations for cesareansection and EXIT procedure at delivery though less frequently needed than with similarly sized teratomas.Congenital MassesCongenital Cysts and Thyroid GoiterThe incidence of neck cysts detected during the fetal periodis unknown but very rare.15 Possible etiologies include thesame pathologies as seen in infants and young childrenincluding branchial apparatus anomalies (Figure 4), thymiccysts, thyroglossal duct cysts, foregut duplication cysts, andneurenteric cysts. In all instances, these fetuses may need tobe followed with serial imaging, as involvement of the airwaywith compromise will necessitate consideration for alternatedelivery plans. The prognosis for these patients is typicallyexcellent following curative surgical excision after delivery.Thyroid goiter is a very rare cause of a fetal neck mass presenting as diffuse enlargement of the thyroid gland and diagnosed most frequently in the late second trimester.15 It may beseen with fetal hyperthyroidism, usually in the setting of maternal Grave’s disease or fetal hypothyroidism, typically in thesetting of maternal antithyroid treatment, maternal iodine deficiency, or maternal antithyroid antibodies. Congenital dyshormonogenesis is the most common cause if maternal thyroiddisease is excluded.15 On ultrasound the thyroid will beenlarged, can vary in echogenicity, and is hypervascular(Figure 5). Direct evaluation of fetal thyroid function requirescordocentesis and, depending upon the underlying cause, willnecessitate various in-utero treatments. Goiters can grow to asignificant size and compromise the airway leading to furtherconsiderations regarding delivery planning.4Figure 3. Cervical LM.Coronal ultrasound withcolor Doppler (A) and coronal, T2-weighted MR image(B) of the neck in a 35-weekfetus demonstrate an avascular transspatial cysticneck mass (blue star),which insinuates aroundthe airway at the level of theglottis and extends inferiorly around the infraglottic airway withintact appearance of the vocal folds (red arrow) and only minormass effect on the airway (green asterisk).Posterior Neck MassesAs mentioned previously, fetal posterior solid neck massesare comparatively rare than anterior neck masses; however,cystic masses in this location are the most common neck massesencountered overall in the fetus.16 Masses in this location fallinto the categories of tumors, vascular malformations, and congenital lesions including occipital encephaloceles, which arebeyond the scope of discussion of this review (Table 1).TumorsVascular tumors, in particular congenital hemangiomas,likely comprise the majority of solid posterior fetal neckmasses17 though the literature remains sparse on the incidence of tumors in this location. Hemangiomas are nowhistologically classified based on the presence of glucose-1transporter into infantile and congenital subtypes with thecongenital form being further divided into those that rapidlyinvolute (RICH) and those that do not (NICH). Congenitalhemangiomas are present at birth and have been diagnosedas early as the first trimester. Although the RICH subtype ismore common, on imaging, both types of congenital hemangiomas appear similar presenting as well-circumscribed solidmasses with internal vascularity and high-flow velocity onultrasound. On MRI, they have heterogeneous signal onT2-weighted images (Figure 6) and may demonstrate flowvoids on EPI sequences related to the high-flow internal vessels and enlargement of the feeding vessels in the neck.Hemangiomas may occasionally calcify or have cysticspaces17 and should not be mistaken for a teratoma. Diagnosisof hemangioma is important as they are associated withhydrops and high-output cardiac failure and therefore requireserial imaging with consideration to fetal echocardiography.The differential diagnosis for posterior solid neck massesincludes very rarely Kaposiform endothelioma, another vascular mass that is typically larger in size, can behave aggressively, and is associated with the Kasabach-Merritt syndrome;

high association of other anomalies, a thorough evaluation ofthe heart, skeletal structures, genitourinary, and central nervous systems should be undertaken when a nuchal LM isencountered and referral for fetal echocardiogram and genetictesting if desired. In the absence of aneuploidy, cardiac malformation, and with normal sonographic anatomy, there is avery high likelihood of a good outcome.19Paraspinal MassesFigure 4. Third branchial cleft cyst. Coronal, T2-weighted MRimage of the neck in a 32-week fetus demonstrates a simpleappearing cyst in the ventral paramedian infrahyoid neck (arrow)extending inferiorly to the level of the thyroid.and other rare rhabdoid, fibrous, and sarcomatous massesincluding fibrosarcomas and myofibromas, which can appearsimilar on MRI with heterogeneous signal on T2 and internalflow voids on gradient echo sequences (Figure 7) but typicallydemonstrate less vascularity on ultrasound compared withhemangiomas.Fetal paraspinal masses are extremely rare with a limited setof differential possibilities arising from cells in the sympatheticneural chain including neuroblastoma and ganglioneuroma.Congenital cervical neuroblastoma is very rare with a reportedincidence of 4.4% of all types of congenital neuroblastomas,the most common location being in the fetal adrenal gland.20On ultrasound, masses are typically solid and contain scatteredcalcifications, areas of necrosis and/or hemorrhage. If suspected, fetal MRI should be performed to evaluate for metastatic disease, which may be seen in the liver, bones, skin,lymph nodes, placenta, and umbilical cord.21 On MRI thesetumors present as solid or mixed solid and cystic vascularparaspinal masses, which may splay the ribs (Figure 8) anddemonstrate internal calcification or hemorrhage. Evaluationof tumor extension into the neural foramina and assessment ofextremity motion are paramount, as the presence of cord compression may lead to consideration for premature delivery.Vascular MalformationsNuchal LM has a reported incidence of 0.75%17 and isunique compared with the nonnuchal LM discussed previouslyin that there is a relatively high association with chromosomalabnormalities, reported up to 51% for those diagnosed in thefirst trimester15 including association with trisomy 21, 13, and18, Turner’s syndrome, several different duplication, andmicrodeletion syndromes and other genetic disorders including Sotos syndrome, Cornelia de Lange, and Roberts syndrome among others.18 As with LMs elsewhere in the neck,these lesions present as large avascular cystic multiseptatedmasses with a propensity for internal hemorrhage. Given theOral Cavity MassesFigure 5. Goiter. Coronal ultrasound demonstrates diffuseenlargement and increased echogenicity in the thyroid gland(star) surrounding the fetal airway (arrow). (Courtesy of Dr. MarioJulio Franco, Clinica Materno-Fetal, Florianopolis, Brazil.)Figure 6. Hemangioma. Axial, T2-weighted MR image in a34-week-fetus demonstrates a heterogeneous signal in posteriorwell-circumscribed neck mass (arrow) with prominent vascularityon ultrasound (not shown).Fetal oral cavity masses are rare though several entitiesencountered in this location have a specific imaging appearance allowing the radiologist to be definitive in their diagnosis. The vast majority of masses encountered in this location5

Figure 7. Myofibroma. Axial EPI image in a 36-week fetus demonstrates prominent internal flow voids (arrow) in a large posteriorcervical mass.are benign22; however, due to their location, they can have asubstantial impact on fetal morbidity and require specializedperinatal management.TumorsTeratomas occurring in the oral cavity are the most rarelyencountered anatomic site, accounting for only 0.47% of allcongenital teratomas.2 Although they often appear to be centered in the oral cavity and project out the mouth, theseFigure 8. Paraspinal neuroblastoma. Sagittal, T2-weighted MRimage in a 30-week fetus demonstrates a mildly T2 hypointenseparaspinal mass, which splays the ribs posteriorly (arrow).6Figure 9. Epignathus. Sagittal CT scan of the face in a 1-day-oldneonate demonstrates a large heterogeneous cystic and solidmass with fat density and internal calcifications centered in theposterior palate (star) extending out of the mouth (not shown)and nasal cavity and extending intracranially (arrow) with secondary obstructive hydrocephalus.masses arise from the palate in cells from the craniopharyngeal canal or Rathke’s pouch.23 On imaging the componentsare heterogenous, solid, and cystic and typically reach a largesize at presentation making them readily detected on screening ultrasound. Ultrasound can variably demonstrate calcifications and internal vascularity. MRI is useful in thesepatients to define the full anatomic extent including establishing the relationship to the airway and evaluating for intracranial extension. These tumors may grow rapidly, thus serialimaging is important. Unfortunately, the prognosis of thesefetuses is very poor due to airway involvement, which canlead to polyhydramnios and the potential for intracranialFigure 10. Epulis. Sagittal, T2-weighted MR image in a 33-weekfetus demonstrates a well-circumscribed, T2 hypointense, pedunculated mass arising from the maxillary gingiva protruding out ofthe oral cavity (arrow).

ConclusionEncountering a fetus with a neck mass can seem daunting;however, the use of an anatomic and systematic approachcan help narrow the differential and, in some cases, providea specific prenatal diagnosis. Familiarity with the appearance of the most commonly encountered congenital neckmasses on both ultrasound and MRI, and knowledge ofsome specific imaging features, which can affect the anteand perinatal clinical management, is critical for optimalpatient outcome.ReferencesFigure 11. Foregut duplication cyst. Sagittal, T2-weighted MRimage in a 24-week fetus demonstrates a well-circumscribed,simple-appearing cyst in the anterior tongue (arrow).extension with secondary hydrocephalus and mass effect(Figure 9).Another entity with a specific imaging appearance in thefetal oral cavity is the congenital granular cell tumor or epulis. These masses are gingival in origin arising from the softtissue of the maxillary or mandibular alveolus with intactunderlying bone. They present most often in the third trimester with a significant female predominance (8–10:1).24 Theimaging appearance is that of a pedunculated mass, whichprotrudes out of the oral cavity (Figure 10). They are hypointense in signal on T2-weighted imaging and ultrasound maydemonstrate a vascular stalk. The prognosis for these patientsis typically excellent, as these rarely impair fetal swallowingor impact the airway, though follow-up with serial ultrasoundto monitor growth and evaluate the extent is advised as occasionally they may grow large and lead to obstruction.Lastly, one may occasionally encounter cystic masses inthe fetal oral cavity. Here, an anatomic approach can helpnarrow the possibilities and provide a useful differential diagnosis. When a simple thin-walled unilocular cystic lesion isencountered in the midline anterior tongue, one should consider a foregut duplication cyst, dermoid, or LM (Figure 11).MRI with diffusion-weighted imaging can occasionally behelpful in differentiating a dermoid/epidermoid, which maydemonstrate reduced diffusivity, though often a definitivediagnosis prenatally is not possible. In the midline base oftongue, a thin-walled unilocular cyst should prompt one toconsider congenital lesions arising from the thyroid includingthyroglossal duct cyst. Finally, in the lateral oral cavityinvolving the sublingual and/or submandibular space, a cysticlesion should prompt consideration of a ranula or LM.1. Cass DL. Impact of prenatal diagnosis and therapy on neonatal surgery. SeminFetal Neonatal Med. 2011;16(3):130-138.2. Tonni G, De Felice C, Centini G, et al. Cervical and oral teratoma in thefetus: a systematic review of etiology, pathology, diagnosis, treatment andprognosis. Arch Gynecol Obstet. 2010;282(4):355-361.3. Harnsberger HR, Glastonbury CM, Michel MA, eds. Diagnostic Imaging:Head and Neck. Philadelphia, PA: Lippincott Williams & Wilkins; 2010.4. Meesa IR, Mukherji SK. A simplified approach to the spaces of the suprahyoid neck. Appl Radiol. 2017;46(4):6-14.5. Barnes L, Eveson JW, Reichart P, et al. Pathology and genetics of head andneck tumors. In: Kleihues P, Sobin LH eds. World Health OrganizationClassification of Tumors. Lyon, France: IARC Press; 2005.6. Riedlinger WFJ, Lack EE, Robson CD, et al. Primary thyroid teratomas inchildren: a report of 11 cases with a proposal of criteria for their diagnosis.Am J Surg Pathol. 2005;29(5):700-706.7. Daskalakis G, Efthimiou T, Pilalis A, et al. Prenatal diagnosis and management of fetal pharyngeal teratoma: a case report and review of the literature.J Clin Ultrasound. 2007;35:159-163.8. Uus A, Zhang T, Jackson LH, et al. Deformable slice-to-volume registrationfor motion correction of fetal body and placenta MRI. IEEE Trans MedImaging. 2020;39(9):2750-2759.9. Lazar DA, Cassady CI, Olutoye OO, et al: Tracheoesophageal displacementindex and predictors of airway obstruction for fetuses with neck masses. JPediatr Surg. 2012;47(1):46-50.10. Oosthuizen JC, Burns P, Russell JD. Lymphatic malformations: a proposedmanagemen

Detroit Medical Center Detroit, Michigan bshah@dmc.org Paul J. Spicer, MD University of Kentucky Lexington, Kentucky paul.spicer4@uky.edu seCtion editors Aiden Abidov, MD John D. Dingell VA Medical Center Gulcin Altinok, MD Detroit Medical Center Steven L. Blumer, MD Nemours/Alfred