Cong. Anom., 26: 321-330,1986 Original

A Case of Sacral Parasite

Shigeki TOKUNAGA, Takayoshi IKEDA, Takeshi MATSUO, Hiroshi MAEDA, Nobuko KUROSAKI* and Hozumi SHIMODA* First Department of Pathology, Nagasaki University School of Medicine, 12-4 Sakamoto-machi, Nagasaki 852, Japan and *First Department of Surgery, Naga- saki University School of Medicine, 7-1 Sakamoto-machi, Nagasaki 852, Japan

ABSTRACT A case of sacral parasite is presented. A parasitic body with an im- complete lower limb was attached to the sacrococcygeal region of a female new- born at birth. The were easily separated by operation two days after birth. The parasite contained well developed small and/or large intestines, a multilocular cyst and a unilocular cyst. Histologically, the wall of the multilocular cyst con- sisted of tissues of three germ layers, such as central and peripheral nervous tissues, mature and immature intestine, pancreatic tissue, bronchial cysts, connective tissue, etc. The thick wall of the unilocular cyst consisted of central nervous tissue and connective tissue. The degree of differentiation of these tissues varied consider- ably. The parasite revealed no organ communication with the autosite. Since the operation, her growth and development have been favorable and no other abnor- malities have been found. Key words: , sacral parasite, diagnosis, pathogenesis

Parasitic conjoined twins consist of incomplete (parasite) attached to the fully developed body of the co-twin (autosite). This is an extremely rare anomaly, especially in the sacrococcygeal region. The present paper describes the anatomy and histopathology with some immunohistochemical findings in the sacral parasite. The pathogenesis and diagnostic criteria of this anomaly are also discussed.

CASE REPORT

A female infant weighing 3,800 g was born at 41 weeks of gestation in a satisfactory course to a healthy 23-year-old primipara. No family history of congenital anomalies and no medication during her pregnancy were noted. Delivery was via vaginal route but slightly prolonged. There was no hydramnion, and the placenta was single and apparently normal. The Apgar score of the infant 322 S. Tokunaga et al. was 8 at one and five minutes. At birth, it was noted that the infant had a conjoined with her sacrococcygeal region (Fig. 1). She was referred to the First Department of Surgery, Naga- saki University School of Medicine for a close examination and possible surgery.

Finding on admission: General condition of the infant was fair. The infant was fully developed in all external aspects except for the parasitic body conjoined with her sacrococcygeal region. On auscultation, the chest and abdomen of the autosite were not remarkable. Laboratory examination revealed a slightly high value of white blood cell count, but otherwise no abnormality was observed. The parasite was completely covered with skin which was continuous with the autosite. A partial skin defect was found in the upper portion of the parasite, and the defect was covered with mem- branous tissue (Fig. 2). The parasite had a short and deformed lower limb containing seven toes, that seemed to be fused feet. A few skin polyps were also present (Fig. 2). Distinct external genitalia were not visible in the parasite. The parasite was motionless and did not react to painful stimuli. X-ray examination of the autosite revealed almost complete formation of a skeleton. The parasite contained a femur, a tibia, a fibula, a round tarsar bone, seven metatarsals, seven sets of phalanges and hypoplastic pelvis, but no vertebral structures were present (Fig. 3). A Barium enema examina- tion of the autosite revealed no intestinal communication with the parasite.

Operative findings: Two days after birth, an operation was performed under halothane anesthesia. A circumferential incision was made at the upper portion of the parasite, where the intestine covered with membranous tissue was contained. A section of this membranous tissue formed a thick strand of fibrous tissue which was attached to the tip of coccyx of the autosite. The autosite and parasite were easily separated by cutting the strand. The nourishing vessels were unclear.

Postoperative clinical course: She was discharged home after three weeks, weighing 3,500 g. Since the operation, her growth and development have been favorable and no other abnormalities have been found.

Patho-anatomical findings: The parasite measured 15.0~10.0x6.5 cm and weighed about 730 g. Fig. 4a shows a cross section of the parasite and Fig. 4b is its schema. The surface of the parasite was covered with skin containing sebaceous glands, sweat glands and hair follicles. The larger skin polyp which arose from the upper site of the parasite had segmental bones, suggestive of a rudimen- tary upper limb. The parasite had abundant subcutaneous adipose tissue, bones of a lower limb and pelvis, well developed small or large intestines (22 cm), a multilocular cyst (5 x 5 x3 cm) with white mucinous fluid and a unilocular cyst (3 x 3 x 2 cm) with yellowish serous fluid. The oral side of these intestines continued to the multilocular cyst. The anal side communicated with a hypoplastic urinary bladder, which entered the pelvis and opened to the anus (Fig. 5). This vesico-rectal (or colonal) fistula was confirmed by microscopic observations that these mucosa showed the transition from intestinal mucosa to transitional cell epithelium (Fig. 6a). Two ducts opening to the skin from the urinary bladder were probably urethra (anterior, smaller) and anus (posterior, larger) (Fig. 5). A distinct layer formation was identified in these intestines (Fig. 6b). Liberkuhn glands and gobiet cells were well developed. Enteric nerve plexus with ganglion cells were present in the submucosal and A case of sacral parasite 323

Fig. 1 External view of the parasitic twins prior to operative removal.

Fig. 2 Close-up view of the parasite. Skin defect (arrows) can be seen. The parasite has a short and deformed lower limb with seven toes, and has some skin polyps (P).

Fig. 3 X-ray photograph of the parasitic twins. In the parasite the bones of the lower limb and pelvis are found, but no vertebral structures are present.

muscle layer. The wall of the multilocular cyst consisted of tissues of three germ layers, such as central and peripheral nervous tissues, pancreatic tissue, well or poorly differentiated intestines, bronchial epi- thelium, cartilage, lymphatic tissue, connective tissue, etc. (Fig. 7). The thick wall of the unilocular cyst had central nervous tissue with a ventricular structure, connective tissue, fat tissue, small blood 324 S. Tokunaga et al.

Multilocular CVR

Urinary bladder b

Fig. 4 (a) Cross section of the parasite. A: Multilocular cyst. B: Unilocular cyst. C: Colon. D: Urinary bladder. E: Femur. (b) Schematic diagram of Fig. 4 (a).

Table 1 Histological findings of the parasite

Ectodermal skin hair, hair follicle sweat, sebaceous gl. CNS peripheral nerve ganglion Endodermal small or large intestines pancreatic tissue bronchial tissue urinary bladder urethra Mesodermal connective tissue fat tissue cartilage bone and bone marrow smooth muscle skeletal muscle Fig. 5 Schematic diagram of vesico-rectal fistula. lymphatic tissue small blood vessel vessels and peripheral nerves (Fig. 8). The skeletal muscles were replaced completely by fat tissue in the lower limb, but a very small amount of them was observed microscopically only in a region adjacent to the pelvis. Table 1 shows the type of organs and tissues observed in the parasite. Heart, thyroid, parathyroid, thymus, lung, liver, spleen, esophagus, stomach, adrenal gland, ovary, uterus, kidney and ureter were not observed.

326 S. Tokunaga et al.

Fig. 7 Histological findings of the multilocular cyst. (a) central nervous tissue without neuron, (b) poorly differentiated intestine and pancreatic tissue, (c) bronchial cyst, (d) cartilage. cording to this classification, the present case is regarded as a sacral parasite. Most cases of parasitic twins have been reported to consist, at least, of pelvic bone and lower limbs without heart, neck and head. From the embryological viewpoint, basic diagnostic criteria of parasitic twins should be similar to those of fetal inclusion () (Iwasaki, 1984). Accordingly, the criteria may be as follows. The parasite is (1) attached to a certain part of the autosite, (2) has a well defined nutrient blood vessels, (3) resembles the fetal structure, (4) has a whole or a part of the vertebra, (5) has highly differentiated organs, and (6) has no histological features of neoplastic proliferation. Most of the

328 S. Tokunaga et al.

Table 2 The classification of parasitic conjoined twins

attached to the head of the autosite (in the head) Epignathus Janus parasiticus Dicephalus parasiticus Orbital parasite

in the body Thoracopagus parasiticus Epigastrius Dipygus parasiticus Notomelus

in the sacrococcygeal region Pygopagus parasiticus Sacral parasite Ischiopagus parasiticus

ing: a parasite has the structure of a part of the body such as a part of a limb, finger or toe, nail, intestine, etc., in its external appearance, while teratoma shows a simple tumor-like mass even if it has these structures within. They have also described that when a parasite was compared to acardius, if a parasite corresponded to acardius amorphus, it should be called a teratoma. In the present case, the parasite has a lower limb, toes and well differentiated intestines. When this parasite is adapted to acardius, this is not acardius amorphus, but is acardius acephalus arrhachis. According to the criteria, the present case would be apparently diagnosed as a parasite. The distinction, however, is very important because a teratoma is strictly a true neoplasm and sometimes has malignant potential. The proliferative activity and the degree of differentiation in the tissue of parasite mostly correspond to those of the autosite. However, some parts of the parasite may show an immature appearance coexisting with mature and well differentiated tissues or organs as shown in the present case. The multilocular cyst itself in the sacral parasite may be regarded as a teratoma. This case should be rather recognized as a parasite with some immature tissue components than a parasite with neoplastic components (teratoma). 3. Pathogenesis Three theories have been propdsed: fission theory, fusion theory and collision theory. Fission theory is that the division of the inner cell mass gives rise to separate monovular twins and conjoined twins. Hamilton (1954) has suggested that if the division of the inner cell mass is imcomplete con- joined twins are formed, and if the separation is grossly unequal, or if one component is better placed so that it can monopolize more of the placental blood then the less favourably situated mass may become a parasite on or within the other twin that is, parasite or fetal inclusion. He has also sug- gested a further possibility that two organizing centers may occur in a single formative area and give rise to twins, and if separation is imcomplete, or if the organizing centers overlap in their spheres of influence, then various forms of Siamese twins will be produced. A case of sacral parasite 329

Potter (1961) also has described that the origin of conjoined twins is probably the same as that of some normal separate monovular twins, the abnormal situation is determined before the end of the second week after fertilization and is caused by formation of two primitive streaks in a single amniotic cavity. If these two centers of growth were not sufficiently separated, the intermediate area would be shared by the two embryos and that conjoined twins would result. The fission theory has been widely accepted by many authors. In sacral parasite as in the present case, the presence of pelvic bones and lower limb is suggestive of formation of the primitive streak and subsequently the notochord and somite in the parasite. Thus, the fission theory is also accept- able in the case of sacral parasite. Furthermore, the presence of central and peripheral nervous tissues, bronchus, pancreas, intestines, urinary bladder and urethra is indicative of the formation of some neural tube, gut and cloaca in the parasite. On the other hand, the absence of the head, heart, branchial organs, kidney, ureter, ovary, uterus, vagina and adrenal gland is of aplasia of cranial neural tube, cardiac mesenchyme, branchial arches and pharyngeal porches, urogenital ridge, ureteric bud, metanephros and some coelomic epithelium in embryonic stage. Fusion theory stipulates that the fusion of monovular twins in the uterus gives rise to conjoined twins. If the fusion occurred at the dorsal surface of the body as in sacral parasite, both autosite and parasite must have their own umbilical cord. However, no cases with separate nourishing vessels were reported. Thus, this theory has hardly been accepted. Guttmacher and Nicholas (1967) have supported the collision theory that the secondary fusion of two separate embryonic axes developed on a single blastoderm. This only differs from the fusion theory in time of occurrence. Stephens et al. (1 982) presented an interesting hypothesis, that is, some types of parasitic twins, which may be considered as ectopic limbs (usually the legs are more completely developed) attached to the midline of the autosite with no indication of ectopic axial structures, may result from duplica- tion of Wolffian ridge. The exact cause of conjoined twins remains unknown.

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