A Case of Sacral Parasite

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 twins 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 consisted 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 abnormalities have been found. Key words: conjoined twins, sacral parasite, diagnosis, pathogenesis Parasitic conjoined twins consist of incomplete twin (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 parasitic twin 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 membranous 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 examination 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 epithelium, 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 (fetus in fetu) (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 Craniopagus parasiticus 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.

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