Kidney Stone: Will It Pass on Its Own or Do I Need Surgery?

A "kidney stone" (kidney stones / nephrolithiasis) and a "ureteral stone" (ureteral stones) often describe the same original problem at a different stage: the stone forms inside the kidney and, if it moves, travels a specific path before reaching the bladder.

• Renal pelvis → ureteropelvic junction (the narrowest point near the kidney)
• Upper ureter (at the level of the iliac vessels)
• Mid-ureter
• Lower ureter → ureterovesical junction (the narrowest point along the entire path) → bladder

The stone's location along this path — not just its size — significantly affects the likelihood of spontaneous passage and the type of treatment usually discussed.

EAU guidelines describe general trends in spontaneous passage likelihood by size, without this being an absolute rule for every patient:

• ≤4-5 mm: relatively high likelihood of spontaneous passage, especially for lower-ureter stones
• 5-7 mm: moderate likelihood of spontaneous passage; a period of observation is often discussed
• 8-10 mm: reduced likelihood of spontaneous passage; active treatment is discussed more often
• 10-20 mm: active treatment (ESWL, RIRS, or PCNL depending on location/composition) is discussed in most cases
• >20 mm: PCNL is discussed more often as a first option, especially for kidney stones

These ranges are general trends from the literature, not automatic decision cutoffs — location, stone composition, and the presence of obstruction or infection can change the discussion entirely, even for the same size.

In the 6-7 mm range, the likelihood of spontaneous passage decreases compared to smaller stones, but does not disappear — especially if the stone is in the lower ureter and is not causing significant obstruction. In this range, a limited period of observation with medical expulsive therapy is often discussed before considering active treatment such as RIRS or ESWL. The decision also depends on how long the stone has remained in the same position, pain intensity, and whether kidney function is affected.

For stones of 10-20 mm located inside the kidney, spontaneous passage is not a realistic expectation in most cases — the stone is simply too large to pass through the normal ureteral diameter without fragmentation. The treatment discussion usually revolves around ESWL or RIRS, with the choice influenced by the location inside the kidney (e.g., lower pole calyx), the stone's density in Hounsfield Units, and the anatomy of the collecting system. Lower-pole stones are generally considered more difficult both for spontaneous passage and for complete clearance after ESWL, due to the direction of gravity.

Two stones of the same size can have entirely different courses depending on their location:

• Lower-ureter stones: generally the most favorable location for spontaneous passage
• Mid-ureter stones: intermediate likelihood, influenced by proximity to the iliac vessels
• Upper-ureter stones: may be associated with more pronounced hydronephrosis if they cause obstruction
• Renal pelvis or lower-pole calyx stones: don't "pass" in the same sense while they remain inside the kidney — the discussion is whether active removal is needed at all

This is why a question like "will my 8 mm stone pass on its own?" doesn't have a single answer without knowing exactly where it is.

Regardless of stone size, the findings below are a reason for immediate — not scheduled — medical evaluation:

• Fever or chills alongside renal colic
• Uncontrolled pain that does not respond to analgesics
• Persistent vomiting with inability to keep down fluids
• Stone in a solitary kidney (a single functioning kidney)
• Significant decrease in urine output or anuria
• Pregnancy with suspected renal colic

These findings, especially the combination of fever with obstruction, are considered a urological emergency and are not managed with simple observation at home.

Extracorporeal shock wave lithotripsy (ESWL) uses shock waves from outside the body to fragment a stone into smaller pieces that can pass naturally. It is discussed more often for small-to-medium stones, especially when stone density on CT (Hounsfield Units) and skin-to-stone distance are favorable. It does not require incisions or general anesthesia in most cases, but may need more than one session, and fragments take time to pass after the session.

Percutaneous nephrolithotomy (PCNL) creates a small skin tract directly into the kidney to remove a large stone burden in a single session. It is discussed more often for stones >20 mm, branching (staghorn) stones, or when previous ESWL/RIRS attempts were not fully effective. It usually requires a short hospital stay and general anesthesia, but offers the highest single-session complete-clearance rates for a large stone burden, according to international guidelines.

Non-contrast CT urography is the primary imaging test for precisely characterizing a stone, as it provides information not equally visible on ultrasound:

• Precise size in three dimensions
• Exact location within the urinary tract
• Density in Hounsfield Units (HU) — an indicator of stone hardness
• Skin-to-stone distance, relevant to the likelihood of ESWL success
• Presence and degree of hydronephrosis
• Number of stones and total stone burden

Stones with higher Hounsfield Unit density tend to respond less well to ESWL, according to systematic reviews of the literature — this is one reason technique selection is based on CT findings, not size alone.

Medical expulsive therapy (MET), usually with alpha-blockers, is used in selected cases to facilitate spontaneous passage of ureteral stones during the observation period. Recent revisions of the EAU guidelines have updated the recommendations on MET, and its use is individualized based on stone size and location. It does not replace the need for monitoring, and it is not a guarantee of passage — it is a supplementary measure discussed within the overall observation strategy.

At Dr. Marinos Vasilas's urology practice in Rhodes, full investigation of kidney and ureteral stones is carried out — from the initial clinical evaluation and urinalysis to CT imaging and the development of an individualized treatment plan: observation, ESWL, RIRS, or PCNL, depending on the case. Urgent cases of obstructive pyelonephritis receive immediate evaluation and decompression.