Chapter 15 Pathology of the Umbilical Cord Embryonic Remnants . 249 Allantoic Duct Remnants . 249 Omphalomesenteric Duct Remnants . 250 Umbilical Cord Coiling, Torsion, and Stricture . 253 Umbilical Cord Length . 255 Cord Diameter . 257 Cord Entanglement and Cord Prolapse . 258 Umbilical Cord Knots . 260 Cord Insertion . 263 Velamentous and Marginal Cord Insertion . 264 Furcate Cord Insertion . 268 Interpositional Cord Insertion . 268 Single Umbilical Artery . 268 Supernumerary Vessels . 270 Thrombosis of Umbilical Vessels . 270 Tumors . 271 Hemangiomas . 271 Teratomas . 272 Miscellaneous Cord Lesions . 272 Selected References . 276 Embryonic Remnants Allantoic Duct Remnants Pathogenesis The allantoic duct arises at about the 16th day postconception, as a rudimentary outpouching of the caudal portion of the yolk sac (see Figure 5.4, page 78). Normally, there is complete obliteration of the allantoic duct at 15 weeks gestation. A remnant, which connects the umbilicus to the bladder, persists as the median umbilical ligament. Occasion- ally, the duct persists as a minute connection to the fetal bladder. Allan- toic duct remnants may be found in 15% of umbilical cords, and for unknown reasons they are more common in males. 250 Chapter 15 Pathology of the Umbilical Cord Pathologic Features Allantoic remnants are most frequently found in the proximal portions of the umbilical cord but may exist discontinuously throughout the cord. They are always located centrally between the two umbilical arteries and consist of a collection of cuboidal or flattened epithelial cells, usually without a lumen (Figure 15.1). The epithelium is generally of the transitional type although mucin-producing epithelium is occasionally found. Rarely, it is accompanied by muscle. Small vessels or vasa aberrantia may be dis- tributed around vessels, and rarely extramedullary hematopoiesis is seen. Clinical Features and Implications In most cases, allantoic remnants have no clinical significance. In 1 in 200,000 births, however, the duct is patent. In this situation there may be urination from the clamped umbilical stump or the presence of cysts that may persist into adult life. Pyelonephritis and abscess formation are common complications of this rare condition. The cysts may become quite large and give the appearance of a “giant” umbilical cord (Figure 15.2). Omphalomesenteric Duct Remnants Pathogenesis Early in development, the midgut communicates with the yolk sac via the umbilical stalk. As the embryo grows the umbilical stalk lengthens and the embryo “prolapses” into the amniotic cavity (see Figure 5.4, page 78). The connection between the gut and the yolk sac becomes attenu- ated and forms the omphalomesenteric (vitelline) duct, which is of endodermal origin. When the gut rotates and withdraws to its original cavity between the 7th and 16th weeks, the duct normally atrophies. Persistence of this duct may then be found in 1.5% of umbilical cords. Remnants of vitelline vessels are found in approximately 7% of cords at term. Figure 15.1. Two remnants of allantoic duct: left patent, right obliterated. Note the absence of the muscular coat. H&E. ¥525. (Courtesy of G.L. Bourne.) Embryonic Remnants 251 Figure 15.2. Edematous umbilical cord of a 32-week fetus with a large urachal extension into the cord. The cord weighed 180g (normal weight is 40g). (Cour- tesy of Dr. S. Kassel, Fresno, California.) Pathologic Features Like allantoic ducts, remnants of omphalomesenteric ducts are more common at the fetal end of the cord. Males also outnumber females 4:1. Remnants are usually present near the periphery of the cord and consist of ducts lined by columnar cells similar to intestinal epithelium (Figures 15.3, 15.4). They often have muscular coats and may occur in pairs. Having an endodermal origin, it is not surprising that remnants of this duct may contain remnants of liver, small bowel, pancreatic tissue, gastric mucosa, ganglion cells, or other intestinal structures. Calcific masses have also been reported. The duct remnants are commonly associated with persistent vitelline vessels (Figure 15.5). These vessels are usually Figure 15.3. Microscopic section of a cord with four remnants of omphalome- senteric duct. The marginal position is typical. H&E. ¥50. 252 Chapter 15 Pathology of the Umbilical Cord Figure 15.4. The omphalomesenteric duct on the left has mucinous epithelium and a small amount of musculature; on the right are the remains of the vitelline vein. H&E. ¥100. tiny but may contain red blood cells. They always lack a muscular coat and are usually composed only of endothelium. Cysts have been described up to 6.0cm in diameter and are frequently surrounded by a plexus of small vessels. Clinical Features and Implications Clinically, these vestiges are unimportant unless there is direct com- munication with fetal bowel, an uncommon occurrence. Remnants of omphalomesenteric ducts can be associated with atresia of the small intestine and Meckel’s diverticulum and are a rare cause of abdominal distension. Figure 15.5. A plexus of small vitelline vessels accompanies the duct remnants (bottom center). At top right is the dilated allantoic duct. H&E. ¥64. Umbilical Cord Coiling, Torsion, and Stricture 253 Suggestions for Examination and Report: Embryonic Remnants Gross Examination: Unless a cyst is present, remnants are usually not identifiable grossly. Comment: Embryonic remnants in the cord usually have no clinical significance unless they have persistent connections to the bowel or bladder. Umbilical Cord Coiling, Torsion, and Stricture Pathogenesis The umbilical cord is usually coiled, twisted, or spiraled, more com- monly in a counterclockwise direction (a “left” twist) in a ratio of about 4:1 (Figure 15.6). The helices may be seen by ultrasonographic exami- nation as early as the first trimester of pregnancy but they increase sig- nificantly during the third trimester. The coils number up to 40, but as many as 380 total turns have been described. The coiling index has been used to evaluate the degree of twisting, defined as the number of coils divided by length of cord. The average coiling index is 0.21/cm. Hypocoiled cords represent about 7.5% of cords, noncoiled cords are present in 4% to 5%, and hypercoiled cords occur in about 20% (Figure 15.7). Hypocoiling and hypercoiling are both associated with adverse perinatal outcome, including an increase in perinatal mortality, intrauter- ine growth restriction, and fetal distress. Twisting of the cord is thought to be the result of fetal activity. Lack of coiling may then reflect fetal inac- tivity as coiling is reduced in cases of uterine constraint, anomalies that restrict fetal movement, and possibly central nervous system (CNS) disturbances. LR Marked Minimal Figure 15.6. Drawing depicting different types of umbilical cord twist includ- ing left (L), right (R), minimal and marked twisting. 254 Chapter 15 Pathology of the Umbilical Cord Figure 15.7. Preterm stillborn infant and placenta with a markedly coiled (twisted) umbilical cord. This was the presumed cause of death. Pathologic Features The degree of coiling tends to be rather uniform throughout the length of the umbilical cord. However, focal areas may show excessive or decreased coiling or excessive coiling may be localized and form a stric- ture (Figure 15.8). Other terms used for these significant reductions in Figure 15.8. Spontaneous abortus at about 14 weeks gestation with markedly spiraled cord and severe constriction of the cord (torsion) near the fetal surface that led to the death. Umbilical Cord Length 255 the diameter of the umbilical cord are constriction, torsion, or coarc- tation. They are often seen in fetal demise and most commonly found at the fetal end of the cord. This may occur because there is a gradually diminishing amount of Wharton’s jelly near the abdominal surface. We are convinced that these are not artifacts, as some have suggested, and the pathologic changes associated with strictures support this. In addi- tion, cord strictures are rarely seen in hypocoiled or normally coiled cords. Pathologic findings associated with stricture and/or hyper- coiling include congestion of the cord and vessels on one side of the torsion, compression, and/or distension of the umbilical vein, long-standing degener- ation of the umbilical vessels, and thrombi in the umbilical or placental surface vessels. Because these fetuses are often macerated and coagulation is inadequately developed in embryos, the demonstration of thrombi is often difficult in early gestation. Suggestions for Examination and Report: Abnormal Coiling or Stricture Gross Examination: Ideally, the direction of the coil or twist and the degree of coiling should be noted (see Figure 15.6). The coiling index described above may be used for this purpose, but may not be necessary if the examiner is experienced. Focal areas with increased or decreased twisting should also be noted. Constric- tions should be sectioned, and attention should be given to the chorionic vessels as these may contain thrombi. Comment: Abnormal coiling or strictures may be associated with adverse perinatal outcome. If a stricture is present in the setting of a fetal demise and there is evidence of venous obstruction, such as thrombosis, the constriction can be considered the cause of death. If supporting histologic findings are not present, the con- striction may be suggested as a cause of demise. Umbilical Cord Length Pathologic Features The normal length of the umbilical cord at term is approximately 55 to 65cm. Excessively long cords occur in 4% to 6% of placentas whereas abnormally short cords have an incidence of approximately 1% to 2%. Short cords are those less than 35cm and long cords are those greater than 70 to 80cm. When evaluating cord length, there are several points that should be remembered. First, it is important to distinguish between “absolute” and “relative” lengths. A cord that is long but wound about the neck multiple times will be functionally short, and this is particularly evident during fetal descent at delivery.