Right thoracic kidney – A rare case report in a female patient

Introduction:

Thoracic kidney is one of the rare forms of congenital malformation with a reported incidence noted 1 in every 10,000 1. Some of the congenital malformations include pelvic kidney, fused kidney (crossed and uncrossed), renal agenesis (unilateral or bilateral), congenital polycystic ovarian disease and ectopic kidneys 2. Among all the renal ectopia, intrathoracic kidney contributes to less than 5% of the total number of reported cases with left side occurrence being more common 3. It also more common among males than in females 4. In majority of the cases this anomaly is an accidental finding in routine radiography as it is almost asymptomatic 5. Thoracic kidney may be classified into i) Renal ectopia with eventration of diaphragm ii) diaphragmatic hernia (congenital/ acquired) iii) rupture of diaphragm due to trauma iv) thoracic kidney with closed diaphragm 6.

The present case was an accidental finding that was diagnosed with right sided intrathoracic kidney in a female patient. As such an occurrence is quite rare, the present case study is being reported. Ethical approval from the institution and consent from the patient was obtained (MMCRI/36/C19).

Case presentation:

A 56-year-old female patient was referred to the radiology department of Madha Medical College Hospital, Chennai, India with the chief complaint of diffuse pain in the epigastric region. There were no other chief complaints. This patient was referred to ultrasonography (USG) abdomen for evaluation.

Investigation:

Ultrasound (USG) abdomen screening was performed, and it was noted that there was an absence of right kidney in the right renal fossa. The left kidney was apparently normal and in situ. No familial history or trauma was reported. After complete scanning of the abdomen, the right kidney was not traceable. This was informed to the patient and further investigation was advised.

Computed tomography (CT)- Abdomen was performed. Eventration of the right dome of diaphragm was noticed in the scout image and a herniated thoracic kidney was suspected. Plain CT scan showed a soft tissue mass in the posterior mediastinum (Figure 1A to H). With patient’s renal function test being normal, contrast enhanced scan was done in order to determine the vascularity of this soft tissue. Arterial phase, venous phase as well as delayed phase was taken in order to visualise renal blood vessels, renal tissue enhancement and for ureter and urinary bladder localisation.

Cross sectional contrast images revealed the presence of right kidney in the posterior mediastinum due to congenital diaphragmatic hernia (CDH) with no hydronephrosis. The hilum of this ectopic kidney was facing antero-inferiorly with its long axis almost in transverse axis. The right adrenal gland was absent. The right ureter was longer, and it opened on the ipsilateral side of the urinary bladder. Other findings that were noticed in this case included herniation of the posterior segment of the liver, the ostium of the right renal artery at the level of T12 vertebra (along with coeliac trunk), hypotrophy right lung with compensatory enlarged left lung, mild compression of azygos vein, inferior vena cava and oesophagus between the hilum of the right kidney and the base of the heart.

Discussion:

Typically, kidneys begin their development in the pelvis and subsequently migrate to their usual anatomical position in the upper abdomen. The ascent of the kidneys is preceded by the descent of the gonads into the pelvis. Caudal growth during embryonic development seems to facilitate the migration of the kidneys out of the pelvis, placing them in their final retroperitoneal location in the renal fossa. By the 9th gestational week, they attain their adult position. Throughout the ascent, each kidney acquires its blood supply from nearby vessels, initially from the external and internal iliac vessels. By the 8th week of development, direct vascular supply from the aorta is established. Any irregularity in the origin of the renal arteries may hinder the cephalic migration of the kidneys, leading to renal ectopia 7.

Various factors can interfere with this developmental process, including teratogens, genetic factors, abnormalities in the meeting of the ureteric bud with the nephrogenic blastema for normal nephrogenesis, or maternal disease affecting metanephric development. Such disruptions may lead to abnormal migration of the kidney, resulting in renal ectopia 8. An unusually higher ascent of the metanephros can cause a defect in the diaphragm, resulting in the subsequent presence of an ectopic kidney in the thoracic cavity 9.

The reason behind the cranial migration of kidneys during embryogenesis is still a topic of debate with different schools of thought. Congenital thoracic kidney may be caused by accelerated cranial migration of the embryonic kidney or delayed diaphragm formation. This suggests that aberrant ascent during embryonic development may lead to the ectopic thoracic kidney anomaly 10. Some studies mention the role of the development of liver and adrenal gland and the persistence of nephrogenic cord in the development of renal ectopia 11.

Understanding of the genetic factors contributing to kidney anomalies is continuously evolving. Though many genes are involved in renal anomalies, specific genetic abnormality involved in ectopic thoracic kidney is yet to be proven. Studies have shown that CDH is linked with karyotyping abnormalities in 15q26, 8p23.1, 4p16.3 deletions, tetrasomy 12 associated syndromes such as Pallister- Killian syndrome, Matthew- wood syndrome and Donnari syndrome 12.

Right ectopic thoracic kidney is a rare condition where the kidney is located in the thoracic cavity instead of the abdominal cavity. It represents less than 5% of all renal ectopias and is more commonly found on the left side. The ectopia can be associated with other congenital malformations such as CDH and pulmonary sequestration. Diagnosis is usually made through imaging techniques such as chest X-ray and computed tomography. The literature on this condition is limited, and there is a scarcity of information on the impact of the ectopia on kidney function 13. Though it is a rare phenomenon, intrathoracic kidney must be considered for differential diagnosis in cases of intrathoracic masses. In majority of cases, the ectopic kidney may be asymptomatic and discovered incidentally through imaging tests. In contrast to other renal ectopias, patients with thoracic kidneys have normal renal function and are usually asymptomatic as was the case in the current patient 14. In terms of the related renal structures, elongated ureter is a constant finding along with thoracic kidneys which is also found in the current patient 15. The level of the renal artery may or may not vary with an elongation of renal artery observed in certain cases. In this patient, the renal artery arises at the level of T12 16.

Ectopic thoracic kidney can present with various symptoms including severe respiratory problems, upper back pain, signs of haemorrhagic shock, and difficulty in breathing. Other symptoms may include chest pain, bilateral leg swelling, and features of malignant hypertension and hypertensive heart disease. Surgical intervention may be necessary in severe cases, but asymptomatic patients do not require treatment as was the situation in the current case. Surgical intervention is advisable in cases where there is kidney blockage or urine backing up to the kidney or in patients with severe respiratory symptoms 17. A systematic review of the literature on intrathoracic kidney found that 68% of cases were symptomatic, with 29% experiencing significant complications such as chronic or end-stage kidney disease. Surgical intervention was required in 26% of cases 18. Complications of intrathoracic kidneys can include pelviureteric junction obstruction (PUJO), renal pelvis stone formation, renal calculi causing obstruction to the superior pole calyces, and malignancy 19. However, in cases of Bochdalek hernia associated with an intrathoracic ectopic kidney, the functionally normal ectopic kidneys are left in situ during repair of the diaphragmatic defect without complications 20. This patient was diagnosed with gastric oesophageal reflux and was prescribed GERD medications. Since the patient had normal renal function and no associated symptoms of thoracic kidney, no intervention was done.

Acknowledgements:

The author would like to thank the patient for the support. The author would also like to thank the department of radiology, Madha Medical College Hospital, Chennai, India, for their help during reporting and post processing of images.

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