Congenital Splenic Cyst

In the fetus, congenital splenic cysts (CSCs) are exceedingly rare and are among the least frequent causes of abdominal cystic masses during the antenatal period. However, they are important as they can be part of the differential diagnosis of any cystic mass located in the fetal upper abdomen. CSCs are often isolated and asymptomatic, and as such usually follow a benign clinical course with no known risk of perinatal complications. They should be differentiated from other cystic masses in the left upper abdominal quadrant of the fetus and postnatal sonographic follow up to monitor the size of the cyst should be considered.

Congenital splenic cysts (CSCs) are fluid-filled lesions located within the splenic parenchyma. There are often small and almost always asymptomatic. However, occasionally they can be large enough to be seen protruding from the internal surface of the spleen and can compress neighboring viscera.¹

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The prevalence of CSCs during prenatal life is not known, but they are considered to be exceedingly rare. Sepulveda et al.² reported a multicenter series of nine cases and reviewed 32 additional cases described in the world literature, mostly as isolated case reports. Subsequently, Sauvageot et al.³ reported another multicenter series of 14 cases, increasing the total number of reported cases prenatally diagnosed by sonography to 55 cases. 

CSCs are thought to be due to involution of pluripotent cells in the splenic parenchyma with subsequent squamous metaplasia, invagination of peritoneal coelomic mesothelium, or arising from dysplastic endothelial cells.¹ However, confirmation of any of these theories are difficult to prove since all but one⁴ of the reported prenatal cases lack pathological examination of the splenic lesion. The reason for spontaneous resolution noted in some of the prenatally diagnosed cases remains unknown.

From the histopathologic point of view, splenic cysts are classified into two main categories as either primary (true cysts) or secondary (pseudocysts), according to the presence or absence of an epithelial lining, respectively. Splenic pseudocysts are secondary to trauma or infection and occur mainly in adults. In contrast, true cysts are seen more frequently in children and are sub-classified into parasitic or non-parasitic forms. All CSCs seen in the perinatal period are categorized as a non-parasitic subtype, which includes epidermoid, dermoid, polycystic, or mesothelial (simple) cysts. Morgenstern⁵ has further classified non-parasitic splenic cysts into four groups, including (1) Congenital (with mesothelial, transitional, or epidermoid cell lining or with characteristic gross appearance (interior trabeculation), despite lack of demonstrable cellular lining); (2) Neoplastic (neoplasms of endothelial origin (lymphangioma, hemangioma) or cystified primary or metastatic tumors); (3) Traumatic (cysts in which there is clear evidence of normal splenic architecture, followed by cystic appearance after documented trauma. Usually from non-resolving subcapsular hematoma); and (4) Degenerative (cystified splenic infarct). The latter classification has the advantage of relying on gross characteristics and avoids the histologic examination for the presence or absence of epithelial lining, which can be misleading in relation to determining the etiology of the cyst.⁵  It seems likely that cysts identified in utero belong to the Morgenstern congenital or degenerative classifications, although this can be confirmed only with pathological evaluation.

Fetal splenic cyst is typically an isolated finding, with no known association with other fetal anomalies. However, detailed examination of fetuses with CSCs have shown a 7% (three out of 41 cases) prevalence of associated anomalies, including one case each of unilateral megaureter, cleft lip and palate, and talipes.² This figure most probably represents the presence of incidentally detected anomalies rather than a true association with other specific anomalies. It is therefore recommended that a detailed fetal anatomic survey should be performed whenever a CSC is found, in order to examine other organs to rule out other anomalies, including systemic microcystic disease.

There is no known recurrence risk for CSCs.

CSC often present as unilocular, homogeneous, anechoic mass located in the fetal upper abdomen. They are often discovered incidentally at the time the upper abdomen is imaged to obtain the measurement of the abdominal circumference. A single cyst is visualized in about 79% of the cases, two cysts in 14% of the cases, and three cysts in 7% of the cases.³ In one case, a septation within the cyst was documented prenatally.² Prenatal diagnosis of a CSC is based on the sonographic detection of a round or oval anechoic structure with smooth walls located in the left upper abdominal quadrant posterior to the stomach. In addition, color Doppler ultrasound can be used to rule out the presence of blood flow signals within the lesion. Although in some cases it is difficult to demonstrate that the cyst is located within the spleen at the initial examination, especially in second-trimester fetuses, a thorough examination upon referral usually reveals that the other abdominal organs including the stomach and duodenum, liver, left adrenal gland, and left kidney appear normal and are clearly separated from the cystic mass, making the diagnosis of splenic cyst straightforward. Most cases of CSCs are diagnosed in the third trimester of pregnancy. Therefore, the increasing implementation of third-trimester sonography in current clinical practice will probably lead to an increasing number of CSCs detected prenatally in the near future.

Differential diagnoses are few and include any fetal upper abdominal cystic mass. As the spleen is clearly located beneath the diaphragm and behind the stomach, this criterion is the most important to be used for differentiating CSCs from other fetal abdominal cystic masses. The latter conditions include any cystic mass from the suprarenal gland, kidney, gastrointestinal tract, and hepato-biliary system, including duodenal obstruction, suprarenal cystic mass, intraabdominal cystic pulmonary sequestration, pancreatic cyst, choledochal and hepatic cysts, and a polycystic or hydronephrotic kidney. After the prenatal identification of a suspected CSC, it is important that a differential diagnosis is undertaken because the prenatal diagnosis of other masses of the left upper abdominal quadrant may have different managements and prognoses.^6-8 Therefore, every effort to identify the precise location of the cyst should be performed. Although the use of fetal magnetic resonance imaging has been reported in few cases,^2,3 it seems that the current resolution of modern ultrasound equipment is sufficiently accurate to determine the exact location, size, and appearance of the cystic mass.

Prenatal diagnosis of a CSC should prompt for a detailed examination of the fetal abdominal organs in order to rule out other causes of cystic abdominal masses. Prenatal diagnosis should also mandate subsequent sonographic follow up to monitor the size of the cyst.

Routine screening for splenic cyst is not indicated.

CSCs in the fetus are frequently relatively stable in size. However, excessive growth has been noted in utero, leading to postnatal surgery.⁴ In the neonatal period, a significant number of these cysts disappear. Children with symptomatic cysts are typically referred for surgery.

CSCs are not associated with perinatal complications, although sporadic cases of rupture and hemorrhage have been reported in children and adults.¹ Once detected prenatally, the parents should be counseled about the typically benign nature of this congenital anomaly, although prenatal follow up should be performed to confirm its exact location and monitor the size of the cyst. Postpartum abdominal sonography and pediatric follow up should be considered in order to rule out significant growth of the cyst in the postnatal period.

1. ^{Hodge MG, Ricketts RR, Simoneaux SF, Abramowsky CR, Elawabdeh N, Shehata BM. Splenic cysts in the pediatric population: a report of 21 cases with review of the literature. Fetal Pediatr Pathol 2012;31:54-62.}
2. ^{Sepulveda W, Ochoa JH, Cafici D, Wong AE, Badano F, Andreeva E, Andreeva EY. Splenic cyst as a rare cause of fetal abdominal cystic mass: A multicenter series of nine cases and review of the literature. Ultrasound 2018;26:22-31.}
3. ^{Sauvageot C, Faure JM, Mousty E, Flandrin A, Forgues D, Prodhomme O, Fuchs F. Prenatal and postnatal evolution of isolated fetal splenic cysts. Prenat Diagn 2018;38:390-394.}
4. ^{Todde G, Bagolan P, Fariello G, Malena S, Ferro F, Mosiello G, Alessandri A. Epidermoid cyst of the spleen in a newborn infant. Prenatal diagnosis and partial splenectomy [in French]. Chir Pediatr 1989;30:172–174.}
5. ^{Morgenstern L. Nonparasitic splenic cysts: pathogenesis, classification, and treatment. J Am Coll Surg 2002;194:306-314.}
6. ^{Nyberg DA and Neilsen IR. Abdomen and gastrointestinal tract. In: Nyberg DA, McGahan JP, Pretorius DH, Pilu G (eds.). Diagnostic imaging of fetal anomalies. Philadelphia: Lippincott Wilkins & Wilkins, 2003;547–602.}
7. ^{McEwing R, Hayward C and Furness M. Foetal cystic abdominal masses. Australas Radiol 2003;47:101–110.}
8. ^{Hyett J. Intra-abdominal masses: prenatal differential diagnosis and management. Prenat Diagn 2008;28:645–655.}

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