Nutcracker Syndrome

What is Nutcracker Syndrome?

Nutcracker Syndrome refers to the impingement of the left renal vein (LRV) located between the abdominal aorta and superior mesenteric artery ^{(4, 5)}. Nutcracker phenomenon and nutcracker syndrome are sometimes used interchangeably in literatures. Although both terms are clinically equivalent, the latter is used for patients who are manifesting the characteristic clinical symptoms of the disorder ⁽²⁾.

This vascular compression may lead to hypertension of the left renal vein and a possible emergence of collateral veins(4). Although most cases are asymptomatic, this syndrome may result to varicocele, ovarian vein syndrome, hematuria, flank or abdominal pain, LRV hypertension, and pelviuteral varices ⁽³⁾.

Signs and Symptoms

Although a vascular disorder, its signs and symptoms are predominantly urological or gynecological ⁽¹⁾. The following are the clinical manifestation of Nutcracker Syndrome.

1. Intermittent macroscopic hematuria coming only from left ureteric orifice due to hypertension of the left renal vein causing rupture of thin-walled varices into the collecting duct system ⁽²⁾.
2. Abdominal or flank pain which is occasionally referred to buttocks and posteromedial thigh. This pain is usually aggravated by sitting, standing, walking, or riding in a vehicle that shakes ⁽²⁾.
3. Varicoceles which is the enlargement of veins inside the scrotum frequently occurring on the left side affecting 9.5% of male patients is caused by increased pressure of the LRV. Venous varicosities may be present around the renal pelvis, upper ureter, and calyx internally. Externally, it may be seen at the buttocks or in the vulvar area (2).
4. Orthostatic proteinuria (protein level >400 mg/dL) that is caused by lysis of red blood cells in the urine ⁽²⁾.
5. Orthostatic intolerance which significantly affects the activities of daily living and is often accompanied by obstruction of LRV in 70% of documented cases ⁽²⁾.

Causes

Image 1. Left Renal Vein (LRV) as it enters in the Left kidney.

Source: dcri.org

Nutcracker Syndrome is caused by stenosis of the left renal vein (LRV) as it passes anteriorly to the aorta through the fork formed by both abdominal aorta (AA) and Superior Mesenteric Artery (SMA). Normally, the angle between the SMA and AA is approximately 450. The mesenteric artery branches out from the abdominal aorta, and before going downwards, it moves 4-5 mm ventrally, thus resulting in an inverted J position. This arrangement prevents SMA from compressing the LRV ⁽¹⁾.

Both SMA and LRV anomalies have been pointed out as the primary cause of Nutcracker Syndrome. Anomalies such as abnormally low lateral origin from the aorta, abnormal configuration of its origin or abnormal branching are the causes that are related to the mesenteric artery.

On the other hand, LRV which passes at the back of the aortaor splitting of the LRV with some of its branches coursed the front and at the back of the aorta accounted for the venous anomalies. Other factors that may contribute to this syndrome are abnormal drooping of the left kidney causing stretch of the LRV over the aorta and abnormally high course of the LRV (1).

Between the LRV and vena cava, the normal pressure gradient is less than 1 mmHg. This may rise up to 3 mmHg in the presence of entrapment leading to rupture of thin-walled septum between the small vein and the collecting system in the renal fornix leading to hematuria ⁽¹⁾.

Radiology

Imaging such as Doppler studies, CT Scan, MR angiography, phlebography with renal vein, and IVC manometer are being used widely to confirm presence of Nutcracker Syndrome ⁽⁵⁾.

However, studies show that among these diagnostic tools, Doppler Ultrasonography which is a non-invasive modality should be the initial assessment tool after Nutcracker Syndrome is suspected clinically, or when there is an increased diameter ratio between the distended and narrow portions on CT Scan and MR imaging ⁽²⁾. The following are the radiologic features of the syndrome.

1. Reduced aorta to SMA angle (normal angle is approximately 450)
2. Stenosis of the left renal vein
3. Presence of collateral pathways: Left Gonadal Vein, collateral pathway
4. Increased in the pressure gradient >3 mmHg on renal venography

Treatment

Treatment of Nutcracker Syndrome has been evolving in the last four decades ranging from observation to nephrectomy, depending on the severity of symptoms ⁽³⁾. The available options are subdivided into four groups, namely Surveillance, Open surgical procedures, Intra- or Extra vascular stents, and lastly Intra-pelvic chemical cauterisation ⁽¹⁾.

Surveillance

Patients with mild hematuria characterized by microscopic hematuria or short periods of painless gross presence of blood in the urine may be followed up closely without treatment. For patients 18 years old and below, non-surgical approach is warranted because there is higher likelihood complete resolution ⁽¹⁾.

Open Surgical Correction

Surgical procedures such as Left renal vein transposition, transposition of the superior mesenteric artery, renal auto transplantation, and gonado-caval bypass are being used to correct this pathology ⁽¹⁾.

1. Left Renal vein transposition involves excision of the LRV at its connection to the inferior vena cava (IVC) then re-joining the LRV with the IVC at a lower level away from the SMA.
2. Transposition of the SMA involves excision of the SMA where it branches off from the abdominal aorta then re-joining the SMA with the aorta at a lower position away from the LRV.
3. Renal auto transplantation involves removal of the diseased kidney and replacing it with a new organ from a live donor
4. Gonado-caval bypass used in patients with pelvic varices.

Stenting

Intravascular stenting is the implantation of metallic stents performed with the guidance of digital subtraction angiography under a local anesthesia. The stent is introduced in the femoral artery going to the LRV. The metallic stent is placed in the narrowed portion of the vein ⁽¹⁾.

Extravascular stenting is the use of a ringed Polytetrafluoroethylene (PTFE) graft placed around the LRV medial to the point of origin of left adrenal and leftgonadal vein to its junction with the IVC ⁽¹⁾.

Image 2. Extravascular stenting using a ringed Polytetrafluoroethylene (PTFE) graft

Source: icvts.oxfordjournals.org

Intrapelvic Chemical Acauterization

This method was used in a patient who presented with intermittent gross hematuria by instillation of 0.1% silver nitrate solution into the renal pelvis using a ureteroscope. However subsequent report showed that this treatment was found to be of no benefit ⁽¹⁾.

References:

1. Ahmed, K., Sampath, R., and Khan, M.S. (2006) Current Trends in the Diagnosis and Management of Renal Nutcracker Syndrome: A Review. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/16431142.

2. Kurklinsky, A., and Rooke, T. (2010). Nutcracker Phenomenon and Nutracker Syndrome. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2878259/.

3. Park, Y.B., Lim, S. H., Ahn, J. H., Kang, E., Myung, S.C., Shim, H. J., and Yu, S.H. (2000) Nutcracker Syndrome: Intravascular Stenting Approach. Retrieved from http://ndt.oxfordjournals.org/content/15/1/99.full.

4. Takeyema, P., Bhatt, S., and Dogra, V. (2012) Nutcracker Syndrome. Retrieved from http://www.medscape.com/viewarticle/774258_4.

5. Weerakkody, Y., and D’ Souza, D., et. al. Nutcracker Syndrome. Retrieved from http://radiopaedia.org/articles/nutcracker-syndrome.