Case #2: Answer

Observations

Routine 18 weeks scan. Several axial images and a longitudinal view were provided.

The first image is a axial section at the level of the stomach, and if one excluded "the bump" in front, that abdominal section would look fairly normal.

The same can be said of this section at the level of the chest. Although the heart is not fully visible, the section was obtained to demonstrate "the bump" in front of the chest. Clearly the chest is not closed properly at the level of "the bump".

Another section at the level of the chest demonstrates some narrowing between the chest and "the bump".

Same findings in this section.

The longitudinal section was very unremarkable, and was included to demonstrate that the baby was essentially unremarkable aside from "the bump".

"The bump"

So, clearly, the major finding is "the bump" and we need to define it more. I had cautioned "Do not shoot from the hip", because I was worried that many would simply consider this to be an omphalocele. Although this looks like an omphalocele, a closer observation demonstrates that on all the views, the aspect of "the bump" the further away from the fetus clearly has bone-like structures. These structures are round in some views elongated in others, they shadow and cause side-lobe artifacts. The best match would thus be bones. These also look too organized to be calcifications such as those in teratoma, although teratoma should be in the differential diagnosis. If we try to characterize those bones a little more they look like long bones from limbs, (look at the 3^rd and 4^th image in particular).

There is another observation that a few of you cleverly made. If "the bump" was an omphalocele, then one would expect something to be missing inside the abdomen of the fetus, yet the longitudinal section shows nice and plumb flanks and not a scaphoid deformity.

So the question is what could look like a soft-tissue mass with "limbs" attached to the front of a fetus?

Clearly teratomas could do this (what can a teratoma not look like !) but there is a better answer: a form of parasitic twin or duplicata incompleta called epigastrius or epigastric heteropagus. This is a drawing of what the baby looked like:

History

There are several examples in the literature of such duplicata incompleta:

Ambrose Paré (the French surgeon) (1530) describes a man with a parasitic head:

Bartholinus (one of the founders of anatomo-pathology, a precursor of Gianluigi Pilu in Bologna, and the man who described the gland of the same name) described Lazarus-Joannes Baptist Colloredo. His duplicata incompleta had one thigh, hands, body arms and a head. The twin breathed but did not swallowed.

Louise L "La dame a quatre jambes" (the four-legged-lady) was born in 1869 and had a twin composed only of 2 legs and a pedicle attachment, very similar to our case.

Finally Laloo, from Oudh (India) had the lower portion of a duplicata incompleta with two legs, a penis (no testicles) and anus. The twin would urinate independently from the host, to the dismay of the latter.

Teaching point

Do not jump on a diagnosis that you know. Make sure that all the observations are taken into account before making a diagnosis.

References

Gould and Pyle: Anomalies and curiosity in Medicine (1899)

Truncal duplication represents one of the rare forms of conjoined twins. We observed a male infant with a truncal duplication; in the host twin no pathology was found except an atrial septal defect and a large omphalocele. The parasitic twin was attached to the xiphoid region (xiphopagus) in an opposite and "horseriding" manner, was acephalic, and had multiple gastrointestinal, genitourinary, and skeletal anomalies. The junction site consisted of lipoid and muscular structures. Surgical separation was done without any difficulty. The abdominal defect was repaired primarily. The host twin is doing well.

Mir E, Sencan A, Karaca I, Gunsar C, Etensel B Truncal duplication: a case report. Pediatr Surg Int 1998 Dec;14(3):227-8

We report on a case of conjoined twinning (CT) consistent with fusion of two embryos followed by resorption of the cranial half of one of them, resulting in a normal male baby with the lower half of a male parasitic twin fused to his chest. Fluorescent in situ hybridization (FISH) studies suggested that the parasitic twin was male, and DNA typing studies demonstrated dizygosity. Although incomplete fission is the usual explanation for conjoined twins, the unusual perpendicular orientation of the parasite to the autosite supports a mechanism observed in mares in which early fusion of two embryos is followed by resorption due to compromised embryonic polarity.

Logrono R, Garcia-Lithgow C, Harris C, Kent M, Meisner L Heteropagus conjoined twins due to fusion of two embryos: report and review. Am J Med Genet 1997 Dec 19;73(3):239-43

{Note: this fusion theory is not supported in the literature, as far as I can find, PJ}

The endoparasitic twin is the most common form of asymmetric fetal duplication (heteropagus). A 2-month-old girl who had a parasitic right lower limb with axial skeleton, vertebral column, uterus, fallopian tube, ovary, and bladder implanted in the sternum region is described as another example of exoparasitic twin, the uncommon form of heteropagus. Unusually, dextrocardia was found in the autosite. This report emphasizes the even progression between the endoparasitic and exoparasitic forms of heteropagus.

Corona-Rivera JR, Acosta-Leon J, Velez-Gomez E, Navarro-Ramirez P, Corona-Rivera A, Corona-Rivera E Unusual presentation of heteropagus attached to the thorax. J Pediatr Surg 1997 Oct;32(10):1492-4

This paper records our experience in the management of 25 sets of conjoined twins seen over a 32 year period (1964 - 1996). The twins were classified into 14 complete and symmetrical sets and 11 incomplete or heteropagus. The 14 symmetrical sets included 9 thoracopagus, 2 ischiopagus, 1 craniopagus and 1 omphalopagus twins. In the incomplete heteropagus group there was 1 ischiopagus, one twin being anencepahlic, 2 dipygus, 5 parasitic, 2 fetus-in-fetu and I cranial and caudal. The management is detailed case by case. Overall 10 of 14 symmetrical sets underwent attempts at separation with 16 surviving the procedure, but there were 3 late deaths. In the incomplete group 10 of 11 were operated on with 9 survivors. The importance of a multi-disciplinary approach, the extensive investigations required pre-operatively to define areas of organ and bony conjunction, congenital anomalies of each twin and surgical teamwork is emphasized. Specific problems encountered were identified. In thoracopagus twins the hearts were of paramount importance as conjuction was usually fatal, being associated with major congenital defects. The greater the extent of thoracic cage fusion the greater the chance of associated severe anomaly. Skin expansion to assist coverage of the defects after separation was of great assistance, as was the use of collagen coated vicryl. Evaluation of the liver and pancreatico-biliary systems with isotope excretion scanning was crucial to pre-operative planning. Where there was fusion of the duodenum a single pancreatico-biliary system could be expected and prior strategies for separation and Roux-en-Y enteric drainage of both pancreatic and biliary secretion should be planned. Gastro-oesophageal reflux led to considerable morbidity in both twins of a thoraco-omphalopagus set. In ischiopagus and dipygus conjoined twins bilateral posterior iliac osteotomies were an essential component to anatomic reconstruction of the pelvic ring and wound closure. Also in this group, due to the frequency and extent of shared genital, urinary and ano-rectal structures, long-term morbidity was expected and a component of this might be due to spinal cord tethering, or as in one of our cases, a progressive hydrosyringomyelia. Timing of separation was ideally set at between 5 and 9 months with 6 to 8 weeks of prior tissue expansion but earlier operation was frequently required because of cardio-respiratory problems or organ failure in one twin. In most cases the goal of obtaining separate, independent and intact individuals was achieved.

Cywes S, Millar AJ, Rode H, Brown RA Conjoined twins--the Cape Town experience. Pediatr Surg Int 1997 Apr;12(4):234-48

A 3-day-old boy baby presented with a cystic umbilical swelling covered mostly by skin and partly by amnion. On the surface, an early embryo-like structure was attached (facial features and limb buds). The deeper aspect of it was composed of large cystic and tubular structures and solid organs resembling liver and spleen. It was labeled as acardiac amorphous parasitic twin, the first of its kind to be reported.

Biswas SK, Gangopadhyay AN, Bhatia BD, Bandopadhyay D, Khanna S An unusual case of heteropagus twinning. J Pediatr Surg 1992 Jan;27(1):96-7

A newborn was admitted to the hospital with a set of accessory lower limbs attached to the distal sternum in addition to omphalocele, intestinal malrotation and interventricular defect. The parasitic twin was removed successfully and the omphalocele was left for conservative treatment.

Olcay I, Zorludemir U, Kivanc F A symmetric double monstrosity. Z Kinderchir 1989 Jun;44(3):174-5

An epigastrius (parasitic twinning in the epigastrium) was delivered via the vaginal route spontaneously and died 37 days later. The autosite had cardiac hypertrophy with VSD, PDA, and PFO and an omphalocele. The liver was partly conjoined. There was a small swelling at the lower part of the autosite"s bifurcated sternum to which the parasitic left pelvis and lower extremity were attached. On the second day after birth, parasitectomy was performed. The amputated specimens consisted of a small left pelvic girdle with a free extremity, a scrotal mass, nipplelike structures and two small protuberances externally. The liver, intestines, two testes, one kidney, one ureter, and the bladder were contained within the omphalocele. Although all of the organs and external structures of the parasite had abnormal histopathological findings, differentiated muscle fibers and submucous and/or myenteric plexus were observed.

Yasuda Y, Ohtsuki H, Torii S, Tomoyoshi E, Clark CF Epigastrius with omphalocele--report of a case. Teratology 1984 Dec;30(3):297-309

Reports of parasitic conjoined twins have appeared rarely in the scientific literature and only one study has included a detailed description of the parasitic extremities. We report here two specimens consisting for the most part of normal hosts with ectopic legs attached to the thorax (case 1, thoracoparasitus) or the abdomen (case 2, gastroparasitus). These two specimens are in agreement with several others reported in the literature in having no sign of vertebral columns. These specimens also exhibit a marked decrease in innervation (case 1) or complete absence of somatic nerves (case 2). This finding is in complete contradiction with the idea of the dependence of limb skeletal structure upon peripheral nerves. The hypothesis is presented that this type of parasitic twin may result from duplication of the Wolffian ridge.

Stephens TD, Siebert JR, Graham JM Jr, Beckwith JB Parasitic conjoined twins, two cases, and their relation to limb morphogenesis. Teratology 1982 Oct;26(2):115-21

BACKGROUND: An adult female goat with rare malformations, which consisted of duplication of the intestinal, lower urinary, and genital tracts as well a pair of parasitic appendages, is presented. METHODS: A complete dissection was performed on a moribund female goat (Capra hircus). RESULTS: The animal had a normal body with a parasitic attachment located within the pelvic region. This attachment was represented by an ovoid, trunk-like, adipose mass that lacked internal organs or vertebrae but that had two fairly well-developed limbs with the normal components of hind limbs. There was duplication involving the external and internal genitalia, the urethra, the urinary bladder, and portions of the small intestine as well as the large bowel, including the anal openings. CONCLUSIONS: An autosite with a duplication involving the hindgut and paramesonephric anlages was identified. These features were compatible with life in utero and postutero and emanated from incomplete twinning (heteropagus twins). A review of the literature also suggests that heteropagus twins are a very rare abnormality in both domestic animals and humans.

Otiang"a-Owiti GE, Oduor-Okelo D, Kamau GK, Makori N, Hendrickx AG Morphology of a six-legged goat with duplication of the intestinal, lower urinary, and genital tracts. Anat Rec 1997 Mar;247(3):432-8

Epigastric heteropagus refers to unequal and asymmetric conjoined twins in which the dependent component (parasite) is smaller and usually attached to the epigastrium of the dominant component (autosite). Epigastric heteropagus is a very rare type of conjoined twins. It is generally assumed that conjoined twins represent a form of monozygotic twinning, but there has been no confirmation of this monozygotic hypothesis. Epigastric heteropagus twins differ in several ways from symmetrical conjoined twins. These include male preponderance, and no major connection of vessels, bowels, or bones. These significant characteristics suggest to the authors that the fusion of two fertilized ova and the atrophy of one fetus resulted in this interesting malformation. However, a DNA study indicated monozygotic origin in their case. The possible pathogenesis was ischemic atrophy of the body structure of the monozygotic conjoined twins at an early gestational age.

Hwang EH, Han SJ, Lee JS, Lee MK An unusual case of monozygotic epigastric heteropagus twinning. J Pediatr Surg 1996 Oct;31(10):1457-60

Incomplete parasitic twinning with the parasite attached at the host"s epigastrium is extremely rare. We report a case of epigastric parasitic twinning where the parasite with a well-developed pelvis and lower limbs had accessory pelvic organs and was attached to the host above an omphalocele. The parasite was excised and the omphalocele managed conservatively by mercurochrome application. A review of the four previously reported cases is presented along with a discussion of the possible etiopathogenesis and nomenclature of this condition.

Chadha R, Bagga D, Dhar A, Mohta A, Malhotra CJ, Taneja SB Epigastric heteropagus. J Pediatr Surg 1993 May;28(5):723-7