KILT syndrome revealed by right iliac fossa pain in an 11-year-old boy: A case report

Abstract

Kidney and Inferior Vena Cava abnormalities with Leg Thrombosis syndrome, an acronym for kidney and inferior vena cava abnormalities with leg thrombosis, is a rare congenital condition that predisposes young patients to deep venous thrombosis. We report on the case of an 11-year-old boy with a recent diagnosis of pulmonary tuberculosis who presented with right iliac fossa pain and inability to walk because of a painful flexed right lower limb. Initial ultrasound was inconclusive for appendicitis because the appendix was not visualized due to bowel gas; it showed no peritoneal fluid or intraperitoneal fat infiltration, but the left kidney was not identified. Contrast-enhanced computed tomography excluded acute appendicitis and abdominal tuberculosis and revealed left renal agenesis with compensatory right renal hypertrophy, agenesis of the infrarenal inferior vena cava and bilateral common iliac veins, left external iliac vein agenesis with a small right external iliac vein, extensive collateral venous drainage, and thrombosis of the right internal iliac, common femoral, femoral, deep femoral, and lumbar veins. Targeted Doppler ultrasound confirmed right iliofemoral venous thrombosis. The association of renal agenesis, inferior vena cava and iliac venous agenesis, and lower-limb venous thrombosis established the diagnosis of Kidney and Inferior Vena Cava abnormalities with Leg Thrombosis syndrome. Anticoagulant therapy was initiated with favorable clinical evolution. This case highlights the importance of considering congenital venous anomalies in children presenting with atypical abdominal or groin pain and lower-limb symptoms and emphasizes the complementary role of computed tomography and Doppler ultrasound in diagnosis.

Introduction

Kidney and Inferior Vena Cava abnormalities with Leg Thrombosis (KILT) syndrome refers to the association of kidney anomalies, inferior vena cava (IVC) abnormalities, and leg thrombosis. The acronym was introduced to describe the coexistence of renal maldevelopment, anomalous caval venous anatomy, and deep venous thrombosis, particularly in young patients [1]. Although rare, the condition is clinically important because congenital interruption, hypoplasia, or agenesis of the IVC may impair venous return from the lower limbs and pelvis, leading to venous stasis, collateral venous pathways, and a lifelong predisposition to venous thrombosis [2,3].

The diagnosis can be challenging because clinical manifestations are nonspecific and may mimic more common emergency conditions, including appendicitis, musculoskeletal pain, abdominal infection, or isolated lower-limb deep venous thrombosis. Moreover, routine ultrasound may detect the venous thrombosis but can miss the underlying congenital IVC anomaly, making cross-sectional imaging essential for complete anatomical assessment [4,5].

We report a pediatric case of KILT syndrome revealed by right iliac fossa pain in an 11-year-old boy initially referred for suspected acute appendicitis or intestinal/peritoneal tuberculosis. The case illustrates the diagnostic contribution of CT in identifying the complete venous and renal anatomy, and the complementary role of Doppler ultrasound in confirming venous thrombosis.

Case presentation

An 11-year-old boy presented to the emergency department with a 3-day history of right iliac fossa pain. His medical history was notable for pulmonary tuberculosis diagnosed 2 months earlier, for which antituberculous treatment had been initiated. He also had a surgical history of right ectopic testis repair during infancy, with no history of renal or abdominal surgery.

On clinical examination, the patient was afebrile and had mild tenderness of the right iliac fossa and right inguinal region. The right lower limb was painful and tender, held in a flexed position at the hip, and the patient was unable to walk or bear weight. There was no bowel transit disorder. Laboratory tests showed a normal white blood cell count and an elevated C-reactive protein level of 70 mg/L.

The initial diagnostic considerations were acute appendicitis and intestinal or peritoneal tuberculosis, given the recent diagnosis of pulmonary tuberculosis. Abdominal ultrasound was initially performed but failed to visualize either a normal or pathological appendix because of overlying bowel gas. There was no intraperitoneal fat infiltration or peritoneal fluid. The left kidney was not visualized in the left renal fossa. Given the inconclusive ultrasound examination and the clinical context, an abdominal and pelvic computed tomography (CT) scan was performed, including unenhanced and portal venous phase acquisitions.

CT showed a laterocecal appendix with a mesoceliac tip. The appendix was well aerated, measured 6 mm in diameter, and showed no adjacent inflammatory changes, excluding acute appendicitis (Fig. 1). The right kidney was normally located but mildly enlarged, measuring 12 cm in long axis, consistent with compensatory hypertrophy. The left renal fossa was empty and occupied by bowel loops, and no ectopic left kidney was identified elsewhere in the abdomen or pelvis, confirming left renal agenesis (Fig. 2).

Fig. 1.

Axial portal venous phase CT image of the abdomen showing a laterocecal appendix with a mesoceliac tip. The appendix is well aerated, normal in size, measuring 6 mm, with no adjacent inflammatory changes (blue arrow).

Fig. 2.

Axial portal venous phase CT image showing the right kidney in its normal anatomical position (red arrow). The left renal fossa is empty and occupied by bowel loops (yellow arrow), with no ectopic kidney identified elsewhere in the abdomen or pelvis, consistent with left renal agenesis.

Further evaluation demonstrated multiple congenital venous anomalies and venous thrombosis. The right internal iliac vein was enlarged and showed a central filling defect with peripheral enhancement, producing a target-like appearance consistent with venous thrombosis (Fig. 3). The thrombosed right internal iliac vein drained directly into ipsilateral lumbar veins, some of which were also thrombosed (Fig. 4). The right common femoral vein was also enlarged and thrombosed, with a central filling defect and surrounding soft-tissue infiltration (Fig. 5).

Fig. 3.

Axial portal venous phase CT image showing an enlarged right internal iliac vein with a central filling defect and peripheral enhancement, producing a target-like appearance consistent with venous thrombosis (purple arrow).

Fig. 4.

Axial portal venous phase CT image showing direct drainage of the right internal iliac vein into ipsilateral lumbar veins, some of which are also thrombosed (red arrow).

Fig. 5.

Axial portal venous phase CT image showing an enlarged right common femoral vein containing a central filling defect, consistent with thrombosis, with surrounding soft-tissue infiltration (blue arrow).

Collateral venous pathways were identified. The right common femoral vein drained into an enlarged laterovesical venous collateral, which was also thrombosed (Fig. 6A). It also drained into an enlarged collateral vein coursing along the right anterior abdominal wall (Fig. 6B).

Fig. 6.

(A and B) Axial portal venous phase CT images showing collateral venous drainage of the right common femoral vein. (A) The right common femoral vein drains into an enlarged laterovesical venous collateral, which is also thrombosed (blue arrow). (B) The right common femoral vein also drains into an enlarged collateral vein coursing along the right anterior abdominal wall (green arrow).

Assessment of the deep venous anatomy showed a normal suprarenal and retrohepatic segment of the inferior vena cava (Fig. 7A). However, the infrarenal segment of the inferior vena cava was completely absent, consistent with infrarenal IVC agenesis (Fig. 7B and C). At the level of the external iliac vessels, the left external iliac vein was not visualized, consistent with agenesis, whereas a small right external iliac vein was identified adjacent to the right external iliac artery (Fig. 8). Both common iliac veins were also absent, with only the common iliac arteries identified (Fig. 9).

Fig. 7.

(A-C) CT evaluation of the inferior vena cava. (A) Axial portal venous phase CT image showing the preserved retrohepatic segment of the inferior vena cava (yellow arrow). (B) Axial portal venous phase CT image showing the aorta (red arrow) and the absence of the infrarenal segment of the inferior vena cava at its expected location (blue arrow). (C) Coronal oblique reconstruction showing the preserved retrohepatic segment of the inferior vena cava (yellow arrow), the preserved suprarenal segment (green arrow), and the absence of the infrarenal segment (blue arrow). The aorta is indicated by the red arrow.

Fig. 8.

Axial portal venous phase CT image obtained just above the inguinal ligament showing the external iliac arteries bilaterally (orange arrows). On the left side, no accompanying external iliac vein is identified, consistent with left external iliac vein agenesis. On the right side, a small venous structure adjacent to the external iliac artery is seen, corresponding to a small right external iliac vein (blue arrow).

Fig. 9.

Axial portal venous phase CT image showing absence of both common iliac veins. Only the common iliac arteries are visualized (red arrows), consistent with bilateral common iliac vein agenesis.

A complementary Doppler ultrasound examination was performed to further assess the venous abnormalities and thrombosis. Ultrasound of the right femoral pedicle showed an enlarged right common femoral vein that was incompressible and showed no color Doppler flow, consistent with thrombosis (Fig. 10A). At the femoral bifurcation, the femoral and deep femoral veins were also incompressible, contained echogenic thrombotic material, and showed no color Doppler flow (Fig. 10B). Doppler ultrasound also confirmed thrombosis of the right internal iliac vein, seen as an enlarged vascular structure located between the right external and internal iliac arteries, containing echogenic material and showing no color Doppler flow (Fig. 11).

Fig. 10.

(A and B) Doppler ultrasound evaluation of the right femoral veins. (A) Transverse ultrasound image of the right femoral pedicle showing an enlarged, incompressible right common femoral vein with absent color Doppler flow, consistent with thrombosis (yellow arrow). The right common femoral artery is shown by the blue arrow. (B) Transverse ultrasound image at the femoral bifurcation showing incompressible femoral and deep femoral veins containing echogenic thrombotic material and showing absent color Doppler flow. The femoral vein is shown by the green arrow and the deep femoral vein by the white arrow. The superficial and deep femoral arteries are shown by the red arrows.

Fig. 11.

Axial Doppler ultrasound image showing the right external iliac artery with normal color Doppler flow (red arrow) and the right internal iliac artery with normal color Doppler flow (green arrow). Between them, an enlarged vascular structure containing echogenic material and showing no color Doppler flow corresponds to thrombosis of the right internal iliac vein previously identified on CT (orange arrow).

The association of left renal agenesis, infrarenal IVC agenesis, bilateral common iliac vein agenesis, left external iliac vein agenesis with a small right external iliac vein, collateral venous pathways, and thrombosis of the right internal iliac, common femoral, femoral, deep femoral, and lumbar veins was consistent with KILT syndrome.

The patient was started on anticoagulant therapy, with favorable clinical evolution. He subsequently regained full extension of the right lower limb and was able to walk.

Discussion

KILT syndrome is a rare entity combining renal anomalies, IVC abnormalities, and lower-limb venous thrombosis [1,2]. Reported renal abnormalities include renal agenesis, aplasia, hypoplasia, dysplasia, or atrophic kidney, while venous abnormalities may include agenesis, hypoplasia, or interruption of the IVC and/or iliac venous system [2,4]. The resulting impairment of venous return promotes venous hypertension and stasis in the pelvis and lower limbs, favoring iliofemoral thrombosis and the development of collateral venous pathways [4,5].

The embryologic basis of IVC anomalies is complex. The IVC develops between the sixth and eighth weeks of gestation through the formation, regression, and anastomosis of the posterior cardinal, subcardinal, and supracardinal veins [6]. The suprarenal, renal, and infrarenal segments have different embryologic origins, which explains the variability of congenital venous anomalies. In our case, the suprarenal and retrohepatic IVC were preserved, whereas the infrarenal IVC and bilateral common iliac veins were absent. The left external iliac vein was also absent, while a small right external iliac vein was identified, with collateral drainage through lumbar, laterovesical, and anterior abdominal wall venous pathways.

The association between IVC anomalies and renal abnormalities is well recognized. Several mechanisms have been proposed, including shared embryologic developmental disturbances and perinatal venous thrombosis with subsequent fibrosis and renal maldevelopment [4,6,7]. In this patient, the empty left renal fossa, absence of an ectopic kidney in the abdomen or pelvis, and compensatory right renal hypertrophy supported true left renal agenesis rather than renal ectopia or postsurgical absence. The absence of any history of renal surgery was an important clinical point confirming the congenital nature of this finding.

The clinical presentation of KILT syndrome is variable. Patients may present with leg swelling, pain, difficulty walking, lumbar pain, abdominal pain, or groin pain, depending on the location and extent of thrombosis and collateral circulation [[2], [3], [4], [5]]. In the pediatric population, presentation may be particularly misleading. In our case, the dominant complaint was right iliac fossa pain in a child with elevated CRP and recent pulmonary tuberculosis, leading to initial consideration of acute appendicitis or abdominal tuberculosis. The painful flexed right lower limb and inability to walk were important clues suggesting a venous or musculoskeletal component, later explained by extensive right iliofemoral thrombosis.

Imaging is central to the diagnosis. Ultrasound is usually the first-line examination for suspected appendicitis or lower-limb venous thrombosis. It can demonstrate incompressibility, echogenic intraluminal thrombus, and absent Doppler flow in thrombosed veins, as shown in our patient. However, ultrasound may be limited by bowel gas, operator dependence, and difficulty in evaluating the retroperitoneal venous anatomy and IVC. Therefore, a negative or incomplete ultrasound does not exclude significant deep venous or congenital vascular disease.

CT or MR venography provides a comprehensive assessment of the renal and venous anatomy, the extent of thrombosis, and the collateral pathways [4,5]. In this case, CT was initially performed to exclude appendicitis and abdominal tuberculosis after inconclusive ultrasound, but it established the diagnosis by showing a normal appendix, left renal agenesis, infrarenal IVC agenesis, bilateral iliac venous agenesis, extensive venous collaterals, and right-sided iliofemoral thrombosis. This illustrates the value of systematic review of vascular anatomy on abdominal CT, particularly in young patients with unexplained abdominal, pelvic, or lower-limb symptoms.

The main differential diagnoses in this clinical setting included acute appendicitis, intestinal or peritoneal tuberculosis, isolated lower-limb deep venous thrombosis, and postoperative or acquired venous obstruction. Acute appendicitis was excluded by visualization of a normal, well-aerated appendix without periappendiceal inflammation. No peritoneal fluid, intraperitoneal fat infiltration, bowel wall thickening, lymphadenopathy pattern, or other CT features suggestive of active intestinal or peritoneal tuberculosis were identified. The combination of extensive congenital venous agenesis, renal agenesis, and lower-limb venous thrombosis favored KILT syndrome rather than isolated acquired thrombosis.

Management of KILT syndrome is not standardized because of its rarity and the limited number of reported cases [4]. Anticoagulation is the cornerstone of treatment for acute thrombosis. Long-term anticoagulation and risk factor control are frequently considered because the underlying congenital venous anomaly persists and may predispose to recurrence [4,5]. In selected severe or refractory cases, endovascular or surgical approaches may be discussed. Our patient improved clinically after anticoagulant therapy, with recovery of lower-limb extension and ambulation.

This case is educational for radiologists because it shows that KILT syndrome may be discovered during evaluation of an apparent abdominal emergency. The diagnosis requires recognition of both components: renal anomaly and congenital venous anomaly with thrombosis. Careful evaluation of the IVC, iliac veins, renal fossae, collateral pathways, and lower-limb veins is essential when imaging young patients with unexplained iliofemoral thrombosis, pelvic pain, or atypical right iliac fossa pain.

Conclusion

KILT syndrome is a rare but important congenital cause of venous thrombosis in young patients. It should be considered when deep venous thrombosis is associated with renal agenesis or hypoplasia and anomalous IVC or iliac venous anatomy. In this case, right iliac fossa pain initially suggested appendicitis or abdominal tuberculosis, but CT revealed left renal agenesis, infrarenal IVC agenesis, bilateral common iliac vein agenesis, left external iliac vein agenesis with a small right external iliac vein, collateral venous drainage, and extensive right iliofemoral thrombosis. Doppler ultrasound confirmed the thrombotic component. Recognition of this syndrome is essential to guide anticoagulant therapy and prevent recurrent thrombotic complications.

Patient consent

Written informed consent was obtained from the patient’s legal guardian for publication of this case report and any accompanying clinical and imaging data. All identifying information has been removed to ensure patient anonymity.