* Address correspondence to Gary M. Joffe, MD, University of New Mexico School of Medicine, Department of Obstetrics and Gynecology, ¶Department of Pathology, 2211 Lomas Boulevard NE, Albuquerque, NM 87131-5286, Phone: (505) 272-6386, FAX (505) 277-7621

Synonyms: Congenital lobar adenomatosis, Cystic adenomatoid malformation of the lung, adenomatoid hamartoma, adenoma pulmonis, congenital bronchiolar malformation.

Prevalence: Approximately 220 cases reported to date. M1.7:F1.

Definition: A pulmonary anomaly characterized by overgrowth of terminal bronchioles. Usually unilateral with variable size and rate of growth giving rise to clinical presentations, ranging from intrauterine fetal demise with hydrops to discovery in childhood after recurrent pulmonary infections.

Etiology: Failure of endodermal bronchiolar epithelium to induce surrounding mesenchyme to form bronchopulmonary segments. Arrest of development probably occurs at 6-8 weeks post-conception; certain lesions may develop at 14-18 weeks post-conception.

Pathogenesis: If several bronchiolar divisions are involved, and if hamartomatous growth of terminal bronchioles continues, mediastinal shift, pulmonary, esophageal and vena caval compression may result in polyhydramnios and fetal hydrops. Neonatal respiratory compromise may result from prolonged compression of normal lung tissue.

Associated anomalies: Bilateral renal agenesis, renal dysplasia, truncus arteriosus, tetralogy of Fallot, ventricular septal defect, hydrocephalus, jejunal atresia, diaphragmatic hernia, enteric cyst, tracheoesophageal fistula, sirenomelia, deformity of clavicle, deformity of cervical spine.

Differential diagnosis: Congenital diaphragmatic hernia, extralobar and intralobar pulmonary sequestration, bronchogenic cyst, mediastinal cystic teratoma, contralateral pulmonary agenesis with fluid distension of remaining lung, mediastinal enterogenous cyst, mediastinal neurenteric cyst.

Prognosis: Can be good in absence of hydrops. Development of hydrops usually signals lethal outcome. Type I lesions (macrocystic, cysts at least 5 mm in diameter) generally have better prognosis than Type II or Type III lesions (microcystic, cysts less than 5mm in diameter). Microcystic lesions are associated with greater pulmonary compression and development of hydrops. Cases of in utero therapy with successful outcome have been reported.

Recurrence risk: Not known to be increased.

Management: See text.

MESH Cystic adenomatoid malformation of lung BDE 2501 ICD9 748.4 CDC 748.411* (also 748.580)

Introduction

Congenital cystic adenomatoid malformation (CCAM) of the lung is a pulmonary developmental anomaly with a full spectrum of clinical presentations. Antenatal ultrasonography may reveal an echogenic or multicystic mass with mediastinal shift, hydrops fetalis, and polyhydramnios; or the lesion may not be discovered until several weeks after birth, when the neonate develops mild respiratory symptomatology. The lesion may not be discovered until childhood, when the patient presents with recurrent bouts of pulmonary infection. Clinical presentation and prognosis are probably dependent upon the type of lesion and its resulting sequelae. We present a case of congenital cystic adenomatoid malformation followed by a discussion of the embryology, pathogenesis, ultrasonographic characteristics, and management of this disease, including in utero therapy.

Case report

An 18-year-old gravida 1 was referred to the Maternal Fetal Medicine clinic at our institution at twenty-six weeks from her stated last menstrual period for evaluation of oligohydramnios discovered on routine ultrasound evaluation. A targeted ultrasound revealed a large, multicystic mass apparently occupying the left hemithorax (Fig.1,2,3).

Figure 1: Transverse scan at the level of the thorax demonstrating a large hypoechoic cystic mass occupying the left hemithorax. Note the marked displacement of the heart to the right (arrow).

Figure 2: Transverse scan at the level of the hepatic vein. The appearance of the cystic mass at this level might suggest the diagnosis of diaphragmatic hernia.

Figure 3: Longitudinal scan demonstrating what appeared to be continuity between the fetal abdomen and thorax, suggestive of diaphragmatic hernia. A separate cystic mass arising in the abdomen was also considered in the differential diagnosis.

The heart was noted to occupy the right hemithorax. In addition, a large cystic mass was noted in the left abdomen. There was marked oligohydramnios. These findings suggested a diaphragmatic hernia with stomach and bowel occupying the left hemithorax and left multicystic kidney.

The patient was offered cordocentesis for genetic evaluation. However, on the scheduled day of the procedure, she noted decreased fetal movement. Ultrasound revealed an intrauterine fetal demise.

The patient subsequently delivered a 1,580g stillborn infant. Findings at autopsy revealed an 8x8x1 cm, multilocular cyst arising from the left lower lobe of the lung (Fig.4,5).

Figure 4: Autopsy specimen revealing a 8x8x1 cm cystic mass arising in the left hemithorax. Small, firm masses of normal lung tissue were noted in both hemithoraces. The diaphragm was intact. The heart was markedly displaced to the right, but was structurally normal.

Figure 5: Cystic mass with small remnant of normal left upper lobe of the lung.

The heart was noted to occupy the right pleural cavity but was otherwise structurally normal. The left hemi-diaphragm was intact but extremely attenuated, extending as far caudad as the left pericolic gutter.

The remaining anatomy, including the kidneys, was normal. Histological evaluation of the pulmonary mass was consistent with congenital cystic adenomatoid malformation, Type I (macrocystic) (Fig.6).

Comments

Congenital cystic adenomatoid malformation is a pulmonary developmental anomaly that may give rise to a full spectrum of clinical presentations. The following section will outline the reasons for the varying presentations and will discuss the embryology, pathogenesis, antenatal ultrasonographic findings, differential diagnosis; in addition, there will be a review of the cases of in utero therapy for the disease.

Embryology

The lower respiratory system begins its development approximately twenty-six days after conception. The laryngotracheal groove develops longitudinally in the floor of the primitive pharynx and is the forerunner of the larynx, trachea, bronchi, and terminal bronchioles. At six weeks post-conception, the endodermally derived terminal bronchioles induce the surrounding splanchnic mesenchyme to begin development of the respiratory component of the bronchopulmonary segment¹. The pseudoglandular period (5 to 17 weeks post-conception) is so named because histologically the developing lung has a gland-like appearance. This is the period of development of the bronchiolar divisions with differentiation into the air-conducting system. As will be seen later, the histologic appearance of Type III congenital cystic adenomatoid malformation is quite similar to the appearance of the developing lung in the pseudoglandular period. The canalicular period (16-25 weeks) resembles Type II congenital cystic adenomatoid malformation. During this period of time, the lumina of the bronchi and bronchioles become much larger, and the lung tissue becomes well vascularized. Respiration is possible at the end of this period with the presence of some terminal sacs (primitive alveoli). During the terminal sac period (24 weeks to birth), proliferation of terminal sacs occurs with marked thinning of the epithelium. Capillaries bulge into the sacs, beginning the facilitation of gas exchange. During the alveolar period (late fetal period to eight years of life), the lining of the terminal sacs attenuates to an extremely thin layer of squamous epithelium. According to Moore, "characteristic mature alveoli do not form for some time after birth"¹.

Pathogenesis

The first report of congenital cystic adenomatoid malformation in the English literature was presented by Ch"in and Tang in 1949². They described a case report of the disease and reviewed the ten other cases which had been described in the world literature up to that time. The findings in the majority of these 11 cases were similar to most case reports found in today"s literature. The disease is almost exclusively limited to one lung, with bilateral involvement being extremely rare. In addition, usually only one lobe of the affected lung is involved. If the bronchus leading to the affected lobe is traced, it is noted to end blindly. The early descriptions of the histologic findings described small and large cysts lined by columnar and cuboidal epithelium. Larger cysts were noted to have elastic fibers and smooth muscle in their walls. Almost all of the cases described in the early literature noted a lack of cartilage surrounding the cystic structures. Some authors noted the presence of tall columnar epithelium that resembled gastric mucosa. Associated findings reported in the early literature almost always included "the constancy of general anasarca"² with most authors noting compression of the venae cavae secondary to marked mediastinal shift. Polyhydramnios was a feature of most of the early case descriptions. Ch"in and Tang"s early description of the pathologic findings form the basis for our understanding of the disease today. They state that "the essential feature is an excessive overgrowth of the bronchioles, especially the terminal bronchioles, which causes the marked enlargement of the lobe, while the development of the alveoli is completely suppressed except at the periphery"². They compared the entity to a hamartoma, but noted that it lacked certain elements found in normal lung such as cartilage and mucous glands.

The next major review of the pathogenesis of cystic adenomatoid malformation was reported by Stocker et al. in 1975³. They stated that by 1975, 70 cases had been reported in the literature, including those of Ch"in and Tang. Their review was of 38 cases found in the files of the Armed Forces Institute of Pathology between 1917 and 1975. In the review of their cases, they noted a male to female ratio of 1.7. Twenty of these infants were preterm, 15 were term, and three were unknown. Nine of the 38 infants were stillborn. In contrast to Ch"in and Tang"s series, 10 of these infants had other congenital anomalies. These anomalies included truncus arteriosus, hydrocephalus; deformity of clavicle, cervical and thoracic spine; jejunal atresia, diaphragmatic hernia, bilateral renal agenesis, tetralogy of Fallot, sirenomelia (including agenesis of ureters, bladder, urethra, uterus, cervix, vagina, gallbladder, descending colon, sigmoid colon and rectum, and imperforate anus), ventricular septal defect, and tracheoesophageal fistula. Interestingly, anasarca was not noted in any of these cases. In twelve liveborn infants, partial or total pulmonary lobectomy was performed. Eleven of these infants survived. Unilateral pulmonary involvement was again the rule, and in 19 cases a single lobe was involved, whereas in 10 cases two or more lobes were affected. The major contribution of this review was to define three distinct variants of congenital cystic adenomatoid malformation based on gross and microscopic examination.

Type I cysts (19 cases) are notable for their large size (up to 7 cm in diameter). These cysts are lined by pseudostratified columnar epithelium with numerous polypoid projections. They overlie a thick wall of smooth muscle and elastic tissue. Mucus-producing cells were occasionally noted. Stocker noted that in two of nineteen cases, an island of cartilage was noted near the area where the cysts communicated with the normal bronchial tree. Smaller cysts were also noted in these lesions and were lined by cuboidal to columnar epithelium. The smaller cysts were noted to contain less smooth muscle and elastic tissue than the larger cysts. Of note was the appearance of alveolus-like structures adjacent to or communicating with the larger cysts. These alveolus-like structures were lined with cells that were indistinguishable from alveolar lining cells, but the structures were two to ten times larger than normal alveoli. Blood vessels were reportedly normal.

The Type II lesion had smaller cysts, usually less than 1 cm in greatest diameter. These cysts are lined by cuboidal to tall columnar epithelium that rarely demonstrated pseudostratification. The walls of these cysts are composed of a thin layer of connective tissue containing discontinuous bands of smooth muscle and elastic tissue rarely more than three to four cell layers thick. Mucus cells are not present in Type II lesions. Of note was the finding of striated muscle between cysts in two of these cases. Cartilage was seen only as a normal component of bronchi located adjacent to the lesion. Blood vessels are normal in the Type II lesion.

The Type III lesion (3 cases in this series) were noted to be firm, bulky masses of lung tissue on gross inspection. Histologically, these lesions were described as having cysts that were 2 to 5mm in greatest diameter. These cysts resembled bronchioles in size and distribution and were lined by ciliated cuboidal epithelium. The cyst walls were composed of thin even layers of smooth muscle. The bulk of the lesion, aside from the cysts, consisted of irregularly shaped alveolus-sized structures lined by nonciliated cuboidal epithelium. Reference is made of their resemblance to the gland-like structures seen during the pseudoglandular period of embryonic development (5 to 17 weeks). Mucogenic cells and cartilage are not present.

In Stocker"s series, the clinical course of sixteen liveborn infants with Type I lesion was described. Seven became symptomatic on the first day of life, two between day one and seven, and the remainder between one to four weeks of life. Ten of the cases of Type II lesion had associated anomalies (outlined above). All of these infants were symptomatic on the first day of life.

Type I and Type III lesions were noted to be bulky lesions, and thus produced the greatest degree of mediastinal shift.

There were only two liveborn infants with Type III lesions in this series, and they were noted to be symptomatic on the first day of life.

The authors of this review attempt to correlate the type of lesion with the time in embryogenesis at which the insult may have occurred. The Type I lesion, with its more mature findings of pseudostratification of epithelium, thick wall of smooth muscle surrounding the larger cysts, mucous glands, and rare foci of cartilage, may occur as late as 49 days post-conception. Type II lesions were frequently associated with other severe congenital anomalies in this series, suggesting earlier timing of aberrant differentiation, probably earlier than 31 days post-conception. Type III lesions, with their pseudoglandular appearance, probably develop early in embryogenesis.

By 1977, Ostor et al. stated that the number of cases reported in the English literature had risen to 142, including those of Stocker⁴. These authors took a different view of the embryogenesis of the disease and state that the insult probably occurred later in gestation (16 to 20 weeks). They stated that the presence of normal alveoli at the periphery of the lesion, with abnormal growth in the center of the lesion, implies failure of canalization of terminal bronchioles and subsequent inability to connect the conducting and respiratory elements. Stated another way, the endodermally-derived conducting branches fail to connect with the mesodermally-derived respiratory branches that cluster about their tips.

In 1978, Bale suggested that while researchers disagreed as to the exact nature of the disease (overgrowth, hyperplasia, hamartoma) and the embryologic timing of pathogenesis (early embryonic period vs. 16 to 20 weeks), all agreed that the defect occurred at the level of the bronchiole⁵. She therefore suggested that the disease be termed "congenital bronchiolar malformation"⁵.

In 1980, Wolf et al, reported on the outcome of 32 liveborn infants at their institution who underwent pulmonary resection at various times in development, ranging from the neonatal period through early adulthood⁶. Unfortunately, as the authors state, "no attempt was made to classify lesions into types as described by Stocker et al"⁶.

Again in 1980, Krous et al. reported a case of a neonatal demise that was found on autopsy to have Type II congenital cystic adenomatoid malformation and bilateral renal agenesis⁷. They note that theirs was the third case in the literature in which bilaterality of the disease process was noted. They also note that the usual findings in bilateral renal agenesis (facial and limb positional defects, i.e. Potter"s syndrome) were mild. They used scanning electron microscopy to demonstrate abundant type 2 pneumocytes within the lesions.

As the cysts were noted to communicate with the normal bronchial tree, they speculate that pulmonary fluid production by the cysts mitigated the findings usually found with bilateral renal agenesis. They speculate that the polyhydramnios often found in congenital cystic adenomatoid malformation is secondary to fluid production by the type 2 pneumocytes lining the cysts.

Others have speculated that the polyhydramnios usually seen in this disease may be due to decreased swallowing secondary to esophageal compression or decreased absorption of lung fluid by the hypoplastic, malformed lungs⁸.

Some authors prefer to classify the type of lesion as microcystic (cysts less than 5mm in diameter) and macrocystic (cysts equal to or greater than 5mm in diameter)⁹. These authors propose that poorer prognosis in microcystic disease is secondary to the development of hydrops and hypoplasia of normal lung tissue.

Antenatal diagnosis

The first description of congenital cystic adenomatoid malformation recorded in the ultrasound literature was in 1975 by Garrett et al¹⁰. By 1981 there were three published cases of antenatal ultrasonographic diagnosis of CCAM⁸.

In 1983, Diwan et al. described the antenatal ultrasonographic features of Type III CCAM¹¹. They describe a large echogenic lesion in the left hemithorax which produced marked mediastinal shift. They note the solid, echogenic appearance of the Type III lesion, in contrast to the fluid-filled cysts characteristic of Type I and Type II lesions. They state that "the tiny Type III cysts produce innumerable interfaces and thus give a solid appearance quite analogous to that of infantile polycystic kidney"¹¹.

In 1983, Pezzuti et al. demonstrated the value of antenatal ultrasonographic diagnosis in patients with CCAM that may have otherwise been missed in the neonatal period¹². A neonate with a normal physical exam and arterial blood gases had been noted on antenatal ultrasound to have a 3 cm cystic mass in the right hemithorax. Surgical resection of the lesion in the neonatal period yielded the diagnosis of Type I CCAM. This case reminds us that a certain percentage of CCAM remains asymptomatic in the neonatal period and presents later in life as recurrent lower respiratory infections.

Both Pezzuti et al.¹² and Mayden et al.¹³ outline the differential diagnosis of CCAM. Other entities include extralobar pulmonary sequestration, bronchogenic cyst, and mediastinal lesions such as enterogenous cyst, neurenteric cyst, or cystic teratoma. The differential diagnosis also includes intralobar pulmonary sequestration.

Sauerbrei has recently described the use of duplex Doppler imaging to establish the diagnosis of pulmonary sequestration and to distinguish between extralobar sequestration (ELS) and intralobar sequestration (ILS)¹⁴. He describes the antenatal diagnosis of a fetal pulmonary mass that is hyperechoic (differential diagnosis includes Type III CCAM) but demonstrating a vessel coursing between the mass and the peritoneal cavity. Duplex Doppler examination of the vessel revealed arterial flow from the peritoneal cavity into the mass and venous flow in the opposite direction, which is typical of ELS. ELS is found outside the pleural cavity, whereas ILS is within the pleura. ILS is also different in that it receives its arterial supply from the systemic circulation like ELS, but its venous drainage is into the pulmonary circulation. As ELS and ILS may mimic CCAM in ultrasound appearance, it is important to diligently search for an anomalous blood supply when attempting to make the diagnosis.

There have been cases reported in the literature in which diagnosis of CCAM has been made with ultrasound in which the mass apparently regressed on serial scans. Saltzman states that "it is difficult to tell whether this apparent improvement resulted from actual shrinking of the lung mass or whether the overall normal fetal growth without growth of the mass gave the illusion of a smaller lesion"¹⁵.

In 1985 and again in 1990, Adzick et al. reviewed their experience with 10 cases of CCAM and reviewed 25 other cases reported in the literature^9,16.

The case presented earlier demonstrates the main pitfall in ultrasonographic diagnosis. Cystic adenomatoid malformation is most often confused with congenital diaphragmatic hernia when evaluating with ultrasound. As demonstrated in Figures 1,2, and 3, the large size of this particular cystic mass did not allow accurate identification of the diaphragm. This case was also quite unusual in that it is the only one found in an extensive search of the literature that demonstrated oligohydramnios. Table I presents a summary of cases and outcome of CCAM by lesion type since 1975.

Table 1: Congenital lobar adenomatosis, summary of the literature.

Case	Age	Ultrasound findings	Outcome
		Type I
122	25 weeks	Multicystic, hydramnios, no hydrops.	Term NSVD, survival after resection.
28	27 weeks	Multicystic, hydramnios, hydrops.	PROM, 30 wks, died after resection.
312	36 weeks	Multicystic, no hydramnios, no hydrops.	Term NSVD, survival after resection.
44	NA	Multicystic, hydramnios, hydrops.	Stillborn.
524	27 weeks	Multicystic, hydramnios, hydrops.	Term NSVD, survival after resection.
625	30 weeks	Multicystic, hydramnios, hydrops.	In utero resolution of hydrops, hydramnios with term NSVD, survival post resection.
727	26 weeks	Multicystic, hydramnios, hydrops.	In utero thoracentesis. After fluid reaccumulated, pigtail catheter placement. PROM at 29 wks. Died after 1 hour of life.
828	30 weeks	Multicystic, hydramnios, no hydrops.	Preterm NSVD at 33 wks. Survival after resection.
929	30 weeks	Multicystic, no hydramnios, no hydrops.	Term NSVD. Survival after resection.
1033	22 weeks	Multicystic, no hydramnios, no hydrops.	Termination of pregnancy.
1116	24 weeks	Multicystic, echogenic, hydramnios, resolved, no hydrops.	NSVD 37 wks. Survival after resection.
1216	32 weeks	Multicystic, hydramnios, resolved, no hydrops.	NSVD 39 wks. Survival after resection.
1316	33 weeks	Multicystic, hydramnios, resolved, no hydrops.	NSVD 39 wks. Survival after resection.
1416	35 weeks	Multicystic, hydramnios, no hydrops.	NSVD 36 wks. Survival after resection.
1516	22 weeks	Multicystic, hydramnios, hydrops.	PROM 25 wks. NSVD. Died after 1 hr of life.
1616	26 weeks	Multicystic, hydramnios, hydrops.	Died after surgery from respiratory insufficiency, Tetralogy of Fallot.
1716	20 weeks	Multicystic, no hydramnios, no hydrops, in utero diagnosis diaphragmatic hernia.	Term NSVD. Survival after resection.
1816	26 weeks	Multicystic, no hydramnios, no hydrops, in utero diagnosis diaphragmatic hernia.	Term NSVD. Survival after resection.
1916	27 weeks	Multicystic, no hydramnios, no hydrops.	Term NSVD. Survival after resection.
2016	33 weeks	Multicystic, hydramnios, no hydrops, in utero diagnosis diaphragmatic hernia.	Term NSVD. Died after resection.
2116	32 weeks	Multicystic, no hydramnios, hydrops.	PROM 33 wks, NSVD. Died 1 hr of life.
2316	33 weeks	Multicystic, no hydramnios, no hydrops.	Fetal thoracocentesis. NSVD 37 wks. Survival after two resections.
2416	24 weeks	Multicystic, hydramnios, no hydrops.	NSVD 37 wks. Survival after resection.
2534	24 weeks	Multicystic, hydramnios, hydrops.	IUFD 24 wks.
		Type  II
2634	29 weeks	Echogenic, hydramnios, hydrops.	IUFD 29 wks.
		Type III
2711	32 weeks	Echogenic, hydramnios, hydrops.	Preterm at 32 wks. Died at 28 min.
2823	29 weeks	Echogenic, hydramnios, hydrops.	Preterm at 30 wks. Died at 2 hours.
2810	32 weeks	Echogenic, hydramnios, hydrops.	Preterm at 34 wks. Stillborn.
3013	28 weeks	Echogenic, hydramnios, hydrops.	PROM 28 wks. Died at 16 hours.
3126	21 weeks	Echogenic, hydramnios, hydrops.	Termination of pregnancy.
3220	24 weeks	Echogenic, no hydramnios, hydrops.	Termination of pregnancy.
3331	18 weeks	Echogenic, bilateral, no hydramnios, hydrops.	Termination after fetoscopy, lung biopsy.
3432	24 weeks	Echogenic, hydrops.	Preterm NSVD at 26 weeks. Stillborn.
3533	24 weeks	Echogenic, hydrops.	Termination of pregnancy.
3616	26 weeks	Echogenic, hydramnios, no hydrops.	PROM 32 wks. NSVD. Survival after resection.
3716	32 weeks	Echogenic, hydramnios, hydrops.	PROM 34 wks. NSVD. Died after 1 hr of life.
3816	30 weeks	Echogenic, hydramnios, hydrops.	NSVD 36 wks. Died after 1 hr of life.
3916	22 weeks	Echogenic, hydramnios, hydrops.	Termination of pregnancy.
4016	24 weeks	Echogenic, hydramnios, hydrops.	Termination of pregnancy.
4134	33 weeks	Echogenic, no hydramnios, no hydrops.	Term NSVD. Survival after resection.
4234	28 weeks	Echogenic, no hydramnios, no hydrops.	Term NSVD. Survival after resection.
4334	28 weeks	Echogenic, hydramnios, hydrops, at 37 wks.	Cesarean section at 37 wks for development of fetal hydrops. Survival after resection.
4434	23 weeks	Echogenic, no hydramnios, no hydrops.	Term NSVD. Survival after resection.
4535	21 weeks	Hydrops.	IUFD 22 wks.
4634	27 weeks	Echogenic, no hydramnios, no hydrops.	Term NSVD. Survival after resection.

NSVD: Normal spontaneous vaginal delivery   IUFD: Intrauterine fetal demise

In utero therapy for CCAM

In utero therapy may hold promise for fetuses with CCAM, even in the presence of hydrops. In 1985, Adzick et al. reported the first case of attempted in utero fetal thoracocentesis for drainage of a large macrocystic CCAM⁹. They state that after draining fifty cc of fluid from three of the largest cysts, the mediastinum transiently shifted into a normal position, but there was rapid reaccumulation of the cyst fluid during the first 24 hours.

The first reported case of successful drainage of this type of pulmonary cyst occurred in 1987 by Nicolaides¹⁷.

In 1987, Clark et al. described a case in which a grossly hydropic fetus had placement of a "double pigtail" catheter for continuous drainage of a large Type I CCAM¹⁸. The hydrops immediately resolved, and the infant was delivered at term. Right middle lobe resection in the neonate revealed macrocystic disease, and the patient has subsequently done well.

In 1989, Nugent et al. describe a case of in utero drainage of a macrocystic CCAM in which the cyst appeared to remain smaller during the duration of the gestation, but was actually much larger when surgically removed during the neonatal period¹⁹. On the basis of their findings and review of the literature, Nugent concludes that "based on the outcome of this patient, it does not appear that in utero decompression of Type I cystic adenomatoid malformation is necessary in the absence of hydrops"¹⁹.

In 1990, Chao et al. described a case in which serial fetal thoracocentesis resulted in the birth of a non-hydropic neonate at 35 weeks²⁰. However, the neonate eventually succumbed to progressive respiratory failure, and autopsy revealed the extremely rare combination of bilateral CCAM, with Type I disease on the right and Type III disease in the left lower lobe. These authors conclude that "bilateral lung involvement with CCAM is rare. Nevertheless, detailed sonographic examination of both lungs is imperative since poor prognosis for bilateral disease should contraindicate therapy in utero"²⁰.

In 1990, Harrison et al. described the in utero resection of CCAM in two fetuses at 27 and 23 weeks gestational age²¹. The first case was technically successful. However, cesarean section was necessary at 28 weeks of gestation secondary to worsening preeclampsia ("maternal mirror syndrome")²¹. Establishment of placentomegaly prior to fetal pulmonary resection resulted in worsening maternal hyperdynamic status that failed to resolve after the fetal surgical therapy. Because there was not enough time to allow expansion of normal lung tissue after surgical resection of the CCAM, the neonate succumbed to respiratory insufficiency. In the second case, the period of time between successful resection of the CCAM and delivery of the neonate was six weeks. Despite delivery at 30 weeks gestation, this infant was well at 5 months of age.

Summary

Congenital cystic adenomatoid malformation is a lesion that is well characterized pathologically with over 200 cases reported in the literature since the original description in 1897. With the emergence of antenatal ultrasonography came the ability to characterize the type of lesion and predict the most likely clinical outcome. The issues yet to be completely answered with this disease are which cases to follow expectantly in utero, and which cases require in utero therapy such as chronic drainage of the cyst or fetal surgical resection of the mass.

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