Enormous ectopic liver tissue at the gastrohepatic ligament: a rare entity at Muhimbili National Hospital, Tanzania

Background Ectopic liver tissue (ELT) is a developmental abnormality in which liver tissue develops at an extrahepatic site without connection to the true liver. It is a rare entity with an incidence of 0.24–0.56% according to data described in laparoscopic or autopsy studies. The detailed mechanism behind the development of ELT is poorly understood. ELT predominantly has an asymptomatic nature, even by means of radiological studies the diagnosis of ELT without surgery or autopsy is difficult. ELT has been reported mostly to be found frequently on the gallbladder and rarely on the gastrohepatic ligament. ELT has increased the potential risk of HCC which makes the resection crucial. Due to its variations anatomically, ELT recognition should gain clinical importance and surgeons need to be aware of these possible disparities.


Background
Ectopic liver tissue (ELT) is a rare developmental abnormality in which normally functioning liver tissue develops at an extrahepatic site without connection to the true liver [1].Also, it has been termed as hepatic choristomas in other literature [2].There are two types of ectopic liver; an accessory liver lobe connected to the liver, and a truly ectopic liver.It differs from accessory liver in that ELT is not connected to the mother liver [3].
The number of reported cases of ELT is less than 100 so far [4] with an incidence of 0.24-0.56%,according to data described in laparoscopic or autopsy studies [5] The detailed mechanism behind the development of ELT is poorly understood but authors believe that it occurs due to aberrant migration during the embryological development of the liver [6].
Collan classified four types of ectopic liver; the first is the ectopic liver, which is not connected to the mother liver but is typically attached to the gallbladder or intraabdominal ligaments.The second is a microscopic ectopic liver, which is occasionally found in gallbladder wall.The third is a large accessory liver lobe, attached to the mother's liver by a stalk (pedunculated liver).The fourth is a small, accessory liver lobe attached to the mother's liver [3].
ELT has been reported mostly to be found frequently on organs in the abdominal cavity including the gallbladder, gastrohepatic and umbilical ligaments, omentum, and stomach.Above the diaphragm, it has been reported in the pleural cavity, mediastinum, lungs, and heart [7].However, the gallbladder seems to be the most frequently affected organ in the abdominal cavity [8].Shigemori described a case of ectopic HCC in the jejunum [9].Cardona et al. reported a case of a primary, well-differentiated HCC arising from ectopic liver tissue in the pancreas [10].There are primarily three different vascular supply patterns of gallbladder-associated ELT; artery arising from cystic artery, vascular pedicle (with/without its own vein) arising from liver parenchyma substance and vascular structures embedded in a mesentery lying from the hepatic site to ELT tissue thus ELT recognition should gain clinical importance and surgeons need to be aware of these possible variations [11].
ELT rarely presents symptomatically and is often diagnosed at autopsy or following surgery for another reason, occasion has been reported to cause symptoms, predominantly chronic abdominal pain secondary to torsion or hemorrhage [12].
Complications that can be associated with ectopic liver are torsion, bleeding into the peritoneum, cirrhosis, and sometimes leading to malignant degeneration to HCC due to metabolic inactivity owing to less efficient vascular and biliary ductal systems, which sometimes might be confused for occult metastases from a primary hepatoma [8].
ELT has increased the potential risk of HCC which makes the resection crucial [13].A high incidence of HCC in ectopic livers was described in Japan with increased neoplastic potential compared to orthotopic liver tissue where in most cases, a malignant tumor was found in the ectopic liver, but not in the mother liver [14].Some authors suggested that the outcome after resection to remove HCC was superior when it involved an ectopic or accessory liver compared to when it involved the mother's liver.However, long-term follow-up data are poor [15].
We herein, report a case of a large ectopic liver attached to the gastrohepatic ligament with main vascular supply from the native left liver lobe and omentum; a rare entity for a patient attended at MNH, Tanzania.

Case presentation
A 59-year-old female from Western Tanzania was presented to our facility with a 2-month history of painless upper abdominal swelling with a gradual increase in size.
At MNH, an abdominal CT scan was performed, revealing a heterogeneous enhancing mass measuring 14.78 × 11.13 cm located at the gastrohepatic region with calcification and a similar enhancement pattern to the liver.Blood supply mainly from the left hepatic artery (Fig. 1).
The patient underwent explorative laparotomy with an upper midline incision which extended to the right subcostal to maximize exposure.The findings were isolated mass at the gastrohepatic ligament 17 cm × 12 cm, firm-soft consistency (Fig. 2) with main vascular supply from the left liver lobe and omentum.The left liver lobe was atrophied and the right lobe was enlarged (Fig. 3).There were no features of liver metastases, lymph node enlargement, or peritoneal carcinomatosis.Other viscera appeared to be normal.Technically difficult dissection was performed to mobilize the tumor, the main vascular supply ligated and divided and other nearby structures were separated from the tumor.The tumor was completely removed and taken for histology.Hemostasis was achieved and the drain tube was secured.Total operative time was about 4 h.Intraoperative blood loss was estimated to be 270 cc, there was no blood transfusion intraoperatively.She had an uneventful recovery, with 200-300 cc bilious drain per day, and on day 14 abdominal drain tube was removed.Post-operative histology results revealed capsulated hepatic parenchyma without the biliary components and limited sinusoids with tissue degeneration (Fig. 4).It is now 1-year post-surgery she is attending our OPD clinic for follow-up and there is no complication.

Discussion
ELT is a very rare entity with an unknown incidence as it is widely felt to be under-reported, subsequently, it is a neglected diagnosis because of the absence of symptoms and lack of awareness [16].A large study that reviewed over 5500 autopsy cases identified only 13 cases of ELT, and another large study that reviewed 1802 laparoscopic cholecystectomy cases identified 12 cases of ELT [15].In our setting, this is the first case to be reported countrywide.
An ectopic liver can lead to benign or malignant diseases.Benign cases in the literature report are less frequent including hemangiomas, adenomas, or focal nodular hyperplasia associated with an ectopic or accessory liver; however, the higher frequency of malignancies could be based on the fact that many benign lesions remain undiagnosed because they are asymptomatic [17].Also, congenital anomalies like omphalocele, caudate lobe agenesis, biliary atresia, and bile duct cysts have been shown to have an association with ectopic liver [18].
ELT is usually asymptomatic and generally found intraoperatively during surgeries performed for another reason, or at autopsy, unlikely our case, which had chronic abdominal pain which is the common presentation for symptomatic one [19].Symptoms are due to complications associated with ELT such as torsion, necrosis, rupture, malignant transformation, and the problems related to compression by mass effect [12].
The most common localization of ELT is an intraabdominal area of which the gallbladder is the foremost site, nonetheless, in our case, it was found along the gastrohepatic ligament which is a rare incident reported [1].It is thought to arise from aberrant migration of hepatic tissue that develops together with cystic structures from a foregut diverticulum and can be appreciated elsewhere intra-abdominally or intrathoracically [11].Similarly, the close relation of the developing hepatic parenchyma cell cords to pars cystica may explain why the gall bladder could be embarked by the ELT [4].An overarching theory has yet to elucidate its development along the gastrohepatic ligament [6].
The diagnosis of ELT without surgery or autopsy is difficult by means of radiological studies.ELT is probably not recognized by radiologists due to the rarity of the condition and the lack of awareness.It can be seen as a soft tissue mass on CT or US imaging [20].The percutaneous biopsy is not recommended because of the risk of malignancy and bleeding [21].
ELT has a completely functional architecture, but may be metabolically handicapped; this may facilitate carcinogenesis because it is being exposed to carcinogenic material for a prolonged duration which facilitates the carcinogenic process, it is likely that biliary drainage is insufficient and/or blood supply is reduced and this is thought to account for the significant observation that ELT seems predisposed to neoplastic transformation independent of the liver proper [22].
The optimal surgical strategy for patients who have cancer of ELT is complete resection of ELT and the attached organ [11].During surgery, it is clinically important to define the ELT and its vascular supply before the dissection because undue traction of tissue during the removal may result in rupture or tear of vascular structure derived directly from the liver substance and nearby organs which could eventually lead to severe bleeding [21].
In our case, post-operative histology for excised mass identified normal liver tissue without malignancy degeneration.This post-operative histopathological examination is crucial as malignant degeneration chances still exist in about 3% of cases, some patients might need to undergo a second surgery for a negative resection margin and regional lymphadenectomy [22].Moreover, due to their abnormal locations, asymptomatic lesions may be misdiagnosed in the absence of histology.When HCC is definitely, histologically confirmed in an ectopic liver, it should be treated with the same approaches used for treating carcinoma in the mother liver as in NCCN [15].

Conclusion
ELT is a rare entity with a predominantly asymptomatic nature.Preoperatively diagnosis is difficult even with images.It has anatomical variation and is hardly found along the gastrohepatic ligament.ELT has increased the potential risk of HCC which makes the resection crucial.Increased awareness of this congenital anomaly may result in increased detection rates.

Fig. 1 Fig. 2 Fig. 3
Fig. 1 Abdominal CT scan; heterogeneous enhancing mass measuring 14.78 × 11.13 cm located at the gastrohepatic region with calcification and similar enhancement pattern to the liver

Fig. 4
Fig. 4 Capsulated hepatic parenchyma without the biliary components and limited sinusoids with tissue degeneration