Introduction

Kidney stones, also referred to as renal calculi, are crystals that deposit within the urinary system. A staghorn calculus is a type of renal stone that sits within the kidney and branches out. 

They are common and are estimated to affect 1-2 in 1000.¹ They often occur due to urinary infection and for this reason are more common in women.^2,3 

Symptoms can include loin-groin pain and painful urination. Treatment usually consists of pain relief, anti-sickness medication and surgery to break down the stone. Read on to learn more about the kidney, risk factors for stones and prevention methods.

Kidney functions

The kidneys have a large number of functions, these include:

• Balancing electrolytes -  This includes the movement of potassium and sodium to regulate the concentration in the blood
• Filtering blood - The kidney contains nephrons which are responsible for filtering waste and toxic products from the blood into the urine
• Maintaining blood pressure - The kidney can detect changes in blood pressure and release renin. Renin increases blood pressure by a pathway which constricts the blood vessels and retains water and salt
• Activating Vitamin D - Our bodies get vitamin D through sunlight and food such as oily fish and red meat. Vitamin D needs to be activated by the kidney to help the body absorb calcium to strengthen bones and teeth
• Produce erythropoietin - Erythropoietin is responsible for stimulating red blood cell development, which in turn will carry oxygen around the body

Kidney injury can be acute or chronic and can impact these functions, leading to decreased urination, fluid retention, fatigue and high blood pressure. 

Kidney anatomy 

To better understand kidney stones, it is important to have an idea of the basic structure of the kidneys. The human body typically has two kidneys which are bean-shaped organs, located on either side of the spine. They are roughly the size of a fist and sit towards the back of the abdomen, just below the ribs. 

The kidneys are made up of cone-like segments called renal pyramids which contain the filtering units called nephrons. There are about a million nephrons in each kidney which act to process the blood.⁴ The waste moves through funnel-like calyces to a central area called the renal pelvis. From here urine will pass down tubes to be stored in the bladder. These muscular tubes are called ureters.

Anatomy of urinary tract- illustration by Sophie Arundel

Stones can be located in the renal calyces, the renal pelvis, the ureters or the bladder. The most common places for stones are demonstrated on the diagram below in purple. A staghorn calculus is a stone which has branches much like the horn of a deer. This type of stone takes up the space of the renal pelvis and extends into at least one calyx.⁵ 

Location of kidney stones- illustration by Sophie Arundel

Types of kidney stones

A kidney stone is a collection of crystals that can be varied in their composition with common types including:

• Calcium (oxalate and phosphate) - these are the most common type, making up 75% of kidney stones.⁶ They often occur as a result of dehydration
• Uric acid - these occur when the urine is acidic, which may be due to a high purine diet (red meat, fish), gout and diabetes ⁷
• Struvite - these are typically linked to urinary tract infections as bacteria produce ammonia which makes the urine more alkaline with a higher pH
• Cystine - makes up less than 1% of stones but is commonly a result of medications such as allopurinol, furosemide and laxatives¹

Staghorn calculi are made up of struvite, so are usually linked to a urine infection that makes the urine more alkaline.

Risk factors

There are many risk factors for renal stones, these include:

• Dehydration - Low intake of water and low urination can lead to an increased risk of renal stones. Dehydration can be secondary to sweating, stress, illness or poor fluid intake. Certain occupations such as surgeons are reported to have higher stones due to difficulty accessing water.⁶
• Medical conditions-  this includes anatomical abnormalities, gastrointestinal problems, genetic conditions and recurrent urinary infections.
• Family history- those who have renal stones are more likely to have a family member who also has renal stones¹
• Diet - Foods containing oxalate (spinach, nuts) and purines (red meats, shellfish) can increase the risk
• Medication- allopurinol, vitamin D, furosemide and certain antibiotics can all increase the risk of stone formation

Struvite stones and therefore staghorn calculi are more common in women as the risk of urinary infection is higher. ^2,3

Symptoms

Sometimes kidney stones are small enough to not cause pain and will pass naturally in urine. Typically symptoms occur when a stone is passed into the ureters as they are thin muscular tubes which will spasm. A staghorn calculus may have less pain than those located in the ureter but without treatment can still lead to complications.³

A stone may block the drainage of urine which can increase the pressure in the kidney, called hydronephrosis. As well, the kidney can become infected leading to fever and nausea.

Symptoms of kidney stones therefore  include:

• Severe loin-groin pain that may come in waves
• Nausea and vomiting
• Blood in urine (haematuria) 
• Painful urination
• Frequent urination
• Intermittent urine stream
• High temperature

Diagnosis

History and examination

The classic symptoms of severe loin-groin pain will often point health professionals to the diagnosis. It is also useful for professionals to establish any risk factors such as medical conditions, medications, smoking status or family history. An examination of the stomach can be useful to locate the pain and help rule out any other diagnoses.

Investigations

• Observations - low blood pressure, high heart rate and high temperature can indicate severe infection (sepsis)
• Urine test - this can show blood in the urine or indicators of urinary infection (nitrites and leukocyte esterase)
• Stone analysis -  if the stone is passed, it can be analysed to establish the composition. This can help with modifying risk factors and preventing recurrence
• Blood tests - this will look for infection markers and renal function 

Imaging

• CT scan - this is often a non-contrast CT scan of the kidneys, ureters and bladder and should be performed within 24 hours
• Ultrasound scan - recommended for children and pregnant people as this type of scan does not contain any radiation
• X-ray -  some stones can be seen on X-ray such as calcium oxalate stones and struvite. These images can be useful to formulate treatment plans and monitor progression

Differential diagnosis

Other conditions may present similarly with severe abdominal pain. These conditions include:

• Ruptured abdominal aortic aneurysm
• Ectopic pregnancy
• Diverticulitis
• Appendicitis
• Cholecystitis

Treatment 

The treatment of kidney stones can be conservative (watch and wait), medical or surgical. The type of treatment used commonly depends on the size, the location, the symptoms and any complications present. Typically if a stone is less than 4mm, it is more likely to pass in the urine and so can be managed conservatively.¹ 

Staghorn calculi are larger due to their branching nature, so need to be treated by surgical methods to break up the stone or remove it directly. A staghorn calculus is often treated with percutaneous nephrolithotomy due to the size of the stone and its location in the kidney. This process is explained below.

Conservative 

• Watch and wait- if the stone is small (<4mm), it may be able to pass in the urine. Approximately 95% of stones this size in the ureter will pass within 40 days¹
• Fluids - if the stone is likely due to dehydration, oral or IV intake of fluid may be necessary to prevent further kidney injury
• Follow up - if the stone has not passed or symptoms worsen, medical or surgical treatment may be required

Medical

• Pain relief - typically a painkiller called diclofenac is given rectally. IV paracetamol may also be used
• Alpha-blockers e.g tamsulosin - these can encourage passage of distal stones by relaxing the muscles in the urinary tract. However, they can lead to side effects such as low blood pressure and nausea⁸
• Antibiotics - these will be used if there are any signs of infection such as fever, high infection markers in the blood or low blood pressure
• Antiemetics - medication such as ondansetron or cyclizine can be used to help with nausea and vomiting

Surgical 

• Ureteric stent insertion - if there are signs of obstruction, a stent can be inserted to open the ureter to allow drainage of urine
• Nephrostomy -  this is a tube that passes from the renal pelvis, through the skin to an external bag. This allows urine to drain and temporarily relieves the obstruction
• Ureteroscopy and laser -  ureteroscopy is the process of passing a camera through the urethra, bladder and ureter to the area of the stone. Tools such as lasers can then be used to break up the stone to smaller pieces which can pass more easily. 
• Extracorporeal Shockwave Lithotripsy (ESWL) -  energy waves from outside the body are targeted to the stone and result in the production of smaller fragments. General anaesthesia is not often required and pain relief will be given to make the procedure as comfortable as possible
• Percutaneous nephrolithotomy (PCNL) -  a camera is inserted through an incision in the skin on the back. Once identified, the stone can be broken up and removed. This technique is required for larger stones located in the kidney
• Open surgery - this is used very rarely if other methods are unsuccessful

Surgical treatments can lead to complications such as bleeding and infection. Additionally, these procedures are performed under general anaesthetic which can also lead to side effects such as nausea, confusion and dizziness.

Prevention

There is a high recurrence rate of kidney stones and 80% of individuals have recurrence within 10 years.¹ Preventative measures can vary based on the type of renal stone. Blood tests can be done to identify any treatable causes of high calcium levels such as hyperparathyroidism.

Calcium stones

• Hydration - a fluid intake of 2.5-3L is generally recommended.¹
• Dietary changes - a reduction of oxalate that can be found in chocolate, nuts and beetroot may be advised
• Medication - potassium citrate or a thiazide medication may be prescribed to reduce calcium excretion and acidity of the urine

Uric acid stones

• Dietary changes - a reduction in purines that can be found in certain meat and fish may help prevent stone formation 
• Medication - allopurinol is a medication that can help reduce the levels of uric acid

Struvite stones

• Medication- Antibiotics to help with urine infections

Staghorn calculi are typically struvite stones which often form secondary to urinary infection. Therefore, antibiotics are given in the short-term to treat infection but there are no guidelines to suggest benefits in the long-term for prevention. ^5,9

Complications

Kidney stones, including staghorn calculi, can lead to complications including:

• Kidney infection
• Obstruction
• Acute or chronic kidney injury
• Renal cell carcinoma
• Renal abscess
• Sepsis

Therefore, it is important to seek medical advice if any symptoms of renal stones are present.

Conclusion

Staghorn calculi are a type of renal stone that sit in the renal pelvis and extend into the calyces. Women are at increased risk of staghorn calculi as they commonly occur with urinary infections. Symptoms of renal calculi include loin-groin pain, nausea and difficulty urinating. CT scans are the gold standard imaging for the diagnosis of renal stones and can be used to help guide treatment. The treatment of stones is varied and depends on the size of the stones. Smaller stones may pass naturally in the urine, whereas staghorn calculi will typically need to be surgically broken down. If not treated successfully, the stone can become infected and even lead to sepsis.