Rib notching is an erosion or indentation along the edge of one or more ribs, visible on a plain chest X-ray, that signals something is pressing on, pulling at, or remodeling the bone. Most commonly, the notches appear along the undersides (inferior margins) of the ribs and point to abnormally enlarged blood vessels rerouting blood around a blocked or narrowed section of the aorta. But the finding is not limited to one disease. Depending on which rib edge is affected and which ribs are involved, the list of possible causes stretches from congenital heart defects to nerve tumors to metabolic bone disease, making rib notching one of the more diagnostically rich incidental findings in radiology.
What Rib Notching Actually Looks Like
On a standard posteroanterior (PA) chest X-ray, normal ribs have smooth, well-defined upper and lower borders. Rib notching shows up as scalloped, wavy, or frankly eroded contours, typically on one margin of the rib. The notches tend to be most visible along the posterior portions of the ribs, roughly where the ribs curve from the spine toward the side of the chest. In mild cases, the irregularity can be subtle enough to pass for a normal variant or a film artifact. In advanced cases, the indentations look like a row of shallow bites taken out of the rib’s edge, and they can be obvious even on a quick read.
The first and second ribs are usually spared even in classic cases because those ribs receive their blood supply from different arterial branches than the lower ribs. This sparing pattern is itself a clue: when a radiologist sees notching that skips ribs one and two but is present from the third rib downward, the cause is almost certainly vascular.
Inferior Rib Notching and Coarctation of the Aorta
The single most well-known cause of inferior rib notching is coarctation of the aorta, a congenital narrowing of the aorta usually located just beyond where the left subclavian artery branches off. When the aorta is pinched at that point, blood has trouble getting through to the lower body via the normal route, so it finds alternate paths. One major detour runs through the intercostal arteries, the small vessels that travel along the underside of each rib. These arteries dilate and become tortuous under the increased flow, and over time the pulsating, engorged vessels erode into the bone from below, creating the characteristic notches.
A case report illustrating this pathway describes rib notching discovered incidentally on a plain chest X-ray, where subsequent CT imaging confirmed a tight two-millimeter juxta-ductal coarctation of the aorta along with multiple enlarged chest wall collateral vessels.1PubMed Central. Incidental detection of late presenting co-arctation of the aorta on chest x-ray: the importance of rib notching The patient had reached adulthood without a diagnosis, and rib notching on a routine film was the finding that set the entire diagnostic workup in motion. That pattern is not unusual: coarctation sometimes goes undetected in childhood, and rib notching on an adult chest X-ray can be the first visual flag.
The notching produced by coarctation is bilateral (present on both sides of the chest) in the majority of cases, because the collateral circulation develops symmetrically. However, when the narrowing involves or sits near the origin of the left subclavian artery, the pattern can become asymmetric. Obstruction of the subclavian artery itself has also been documented as a cause of unilateral rib notching on the affected side.2Radiology. Rib notching following subclavian artery obstruction Any condition that forces unusually high flow through the intercostal arteries can, in principle, produce the same erosive effect.
Other Vascular Causes of Inferior Notching
Coarctation dominates the textbooks, but it is not the only vascular culprit. Several other conditions push extra blood through the intercostal arteries and can erode the ribs from below.
- Subclavian artery obstruction: Whether from atherosclerosis, surgical ligation (as in certain older Blalock-Taussig shunt procedures for congenital heart disease), or Takayasu arteritis, a blocked subclavian artery forces blood to reroute through chest wall collaterals, producing notching on the same side as the blockage.
- Pulmonary arteriovenous malformations: These abnormal connections between pulmonary arteries and veins can increase intercostal blood flow in certain configurations.
- Aortic thrombosis or mid-aortic syndrome: Any acquired or congenital narrowing of the aorta below the arch can mimic the hemodynamics of coarctation and generate collateral flow through the intercostal network.
In all of these, the mechanism is fundamentally the same: blood that would normally flow through a larger central vessel gets shunted into the intercostal arteries, which enlarge, pulsate against the undersurface of the ribs, and slowly carve grooves into the bone. The notching tends to take years to develop, which is why it is more commonly found in adults or older children rather than infants, even when the underlying defect has been present since birth.
Neurogenic Causes
Not all rib notching comes from dilated blood vessels. Tumors that grow along the intercostal nerves can press directly on the rib margins and erode bone by mechanical pressure. The clearest example involves neurofibromatosis type 1 (NF1), a genetic condition in which tumors called neurofibromas develop along peripheral nerves throughout the body. When neurofibromas form on the intercostal nerves, they sit in the groove on the underside of the rib and can produce inferior rib notching that looks, on a plain film, remarkably similar to the vascular variety.3European Society of Radiology. Skeletal manifestations in Neurofibromatosis type I – Section: Chest Wall
The distribution of notching in NF1 can offer a clue. Neurogenic notching may be more focal or asymmetric than the bilateral, diffuse pattern of coarctation, because the neurofibromas do not necessarily develop symmetrically along every rib. Other skeletal findings of NF1, like scoliosis or a “ribbon rib” deformity where the rib thins and twists, may also be present on the same film and point the radiologist away from a vascular explanation. Still, the distinction is not always straightforward on imaging alone, and correlation with clinical history is essential.
Superior Rib Notching
When the erosion is on the upper (superior) margin of the rib rather than the lower margin, the diagnostic playbook changes entirely. Superior rib notching is far less common and points to a different group of conditions, because the structures that run along the top of the rib are different from those running along the bottom. The intercostal vein, artery, and nerve all travel in a groove on the rib’s inferior surface, so vascular engorgement erodes the bottom edge. The superior surface is mainly in contact with the intercostal muscles above and does not normally bear a pulsating vessel.
Conditions linked to superior rib notching include connective tissue diseases, paralysis-related muscle wasting, and metabolic bone disorders. In progressive systemic sclerosis (scleroderma), particularly the diffuse form, superior rib notching has been documented. One study comparing the CREST variant of scleroderma with diffuse scleroderma found that superior rib notching occurred exclusively in patients with the diffuse form of the disease.4PubMed. Pulmonary function in progressive systemic sclerosis. Comparison of CREST syndrome variant with diffuse scleroderma The mechanism is thought to involve connective tissue changes and vascular compromise in the soft tissues overlying the rib.
In traumatic quadriplegia, superior marginal rib defects have been described along the posterior portions of the third through seventh ribs. A study of hospitalized quadriplegic and paraplegic patients found resorptive defects in the ribs of quadriplegic patients, attributed to intercostal muscle atrophy and the resulting loss of mechanical stress on the bone.5PubMed. Superior marginal rib defects in traumatic quadriplegia When muscles stop pulling on bone, the bone remodels and thins in the areas where that stress used to exist. This is the same principle behind astronaut bone loss or the thinning of a limb bone after prolonged immobilization, but here it shows up as visible notching on the rib’s upper edge.
Hyperparathyroidism, in which excess parathyroid hormone accelerates bone resorption, can produce subperiosteal bone erosion throughout the skeleton. In the ribs, this resorption can create a scalloped appearance along the superior margin that resembles notching on a chest X-ray.6European Society of Radiology (MyESR). Seeing beyond the lungs: paths to a new approach of analyzing the ribs – Section: Metabolic bone diseases Unlike the focal erosions of vascular notching, hyperparathyroid changes tend to be more generalized across multiple skeletal sites, so the radiologist usually sees other clues elsewhere in the image.
Why the Location on the Rib Matters
Radiologists pay close attention not just to whether rib notching is present but to where on each rib it appears. Vascular notching from coarctation concentrates on the posterior aspects of the ribs, roughly from the rib head to the posterior axillary line, because that is where the dilated intercostal arteries run closest to bone. The anterior portions of the ribs are usually spared in coarctation because the anterior intercostal supply comes from the internal mammary artery, a separate system that is not as involved in the collateral detour.
Neurogenic notching from intercostal nerve tumors can appear anywhere along the rib where the tumor sits, but it tends to be near the costovertebral junction (where the rib meets the spine) because that is where the intercostal nerve exits and where neurofibromas commonly arise. Metabolic erosion from hyperparathyroidism or connective tissue disease is less anatomically constrained and can involve longer segments of the rib margin.
Unilateral versus bilateral involvement adds another layer of information. Bilateral inferior notching strongly suggests a systemic cause like coarctation or bilateral vascular collateral development. Unilateral notching, particularly on the left, raises the possibility of a Blalock-Taussig shunt on that side, a left subclavian artery obstruction, or a local process like a nerve tumor. If notching is bilateral but more pronounced on one side, the asymmetry can help narrow the differential further.
How Rib Notching Gets Discovered
Most rib notching is found by accident. A chest X-ray obtained for an unrelated reason, a preoperative screen, or a workup for high blood pressure leads a radiologist to notice the irregular rib contours. In the coarctation scenario, this incidental detection can be genuinely life-changing: undiagnosed coarctation is associated with premature hypertension, heart failure, aortic dissection, and stroke, and catching it even in adulthood allows for surgical or catheter-based repair. The case report of a late-presenting coarctation discovered through rib notching on a routine film illustrates how a seemingly minor radiographic detail can uncover serious cardiovascular disease.1PubMed Central. Incidental detection of late presenting co-arctation of the aorta on chest x-ray: the importance of rib notching
Once rib notching is identified, the next step is typically cross-sectional imaging, most often CT angiography or MR angiography. These studies can directly visualize whether the aorta is narrowed, whether collateral vessels are enlarged, or whether a mass is pressing on the ribs. If the notching is superior rather than inferior, the workup shifts toward checking parathyroid hormone levels, evaluating for connective tissue disease, or reviewing the patient’s neurological history.
Rib Notching in Children Versus Adults
One question that comes up in clinical practice is why rib notching from coarctation is rarely seen in very young children, even when the coarctation has been present since birth. The answer is time. The collateral vessels need years of increased flow before they enlarge enough to erode bone, and children’s ribs are softer and more cartilaginous, making visible notching less likely to develop quickly. Most references describe rib notching from coarctation becoming radiographically apparent after age five or six, with increasing prevalence through adolescence and adulthood. An infant with a severe coarctation may present with heart failure or poor femoral pulses, but rib notching on the X-ray is not expected at that stage.
This age-related timeline has practical implications. Pediatricians should not rely on rib notching to screen for coarctation in young children, because its absence does not rule the condition out. Conversely, finding rib notching in a teenager or young adult who has never been evaluated for congenital heart disease should prompt an urgent cardiovascular workup.
What Happens After Treatment
If coarctation is repaired, either surgically or with a catheter-based stent, the question arises whether the rib notching will go away. The evidence suggests that it can regress, at least partially. Once normal blood flow through the aorta is restored, the collateral vessels are no longer needed, so they gradually shrink. As the pulsatile erosion stops, the ribs can remodel over time. Complete resolution is not guaranteed, particularly in adults whose ribs have been eroded over many years, but improvement has been documented in follow-up imaging after successful repair. The degree of recovery depends on how long the collateral circulation was active and how much bone was lost before treatment.
For neurogenic causes like NF1, removing the offending neurofibroma can halt further erosion, but the existing bone defects tend to persist because bone regeneration in areas of tumor-related destruction is limited. In metabolic causes like hyperparathyroidism, correcting the underlying hormonal imbalance (through surgery to remove a parathyroid adenoma, for instance) can stop the accelerated bone resorption, and some degree of remineralization is possible over months to years.
Conditions That Mimic Rib Notching
Not every irregularity along a rib margin is true rib notching. Several normal variants and imaging artifacts can fool the eye. Companion shadows, thin soft-tissue lines that run parallel to the inferior rib margin, are common on chest X-rays and can create the illusion of a double contour. Costal cartilage calcification in older adults sometimes produces a bumpy appearance near the anterior rib ends that looks unusual but is benign. Healed rib fractures, particularly those with callus formation, can create focal irregularities that mimic a single notch.
Prior chest tube placement or thoracotomy can leave grooves or defects in the ribs that are purely surgical artifacts. The key distinguishing feature is clinical context: a single focal defect at a known surgical site is very different from bilateral posterior notching across ribs three through nine. When there is any ambiguity, CT imaging resolves the question quickly by showing the three-dimensional anatomy of the rib and any adjacent vascular or soft tissue structures.
Rib Notching as a Teaching Point in Radiology
Within radiology training, rib notching holds a somewhat outsized reputation relative to how often it is actually encountered. It shows up reliably on board exams, case conferences, and teaching files because it is a textbook example of how a small finding on a plain film can reveal a major underlying diagnosis. The logical chain from notched ribs to dilated intercostals to collateral flow to aortic narrowing is a satisfying diagnostic puzzle, and it teaches trainees to look beyond the lungs when reading a chest X-ray. Many radiologists go through entire careers seeing only a handful of true rib-notching cases, yet every trained radiologist can recite the differential diagnosis because it is drilled so extensively in training. The finding’s rarity in daily practice makes it paradoxically easy to overlook when it does appear, precisely because radiologists may not expect to encounter it outside an exam setting. Case reports documenting late-presenting coarctation found through incidental rib notching serve as reminders that this finding, however uncommon, carries real diagnostic weight when it turns up.1PubMed Central. Incidental detection of late presenting co-arctation of the aorta on chest x-ray: the importance of rib notching