Imaging

Because of its non-specific presentation, WS requires imaging for diagnosis, as clinical history and physical exam alone are insufficient. Ultrasound (US) is usually the first exam requested in an emergency context, followed by computed tomography (CT).

• Ultrasound

Hemodynamically stable patients are often evaluated by US initially. Renal hematomas can be hypoechoic, hyperechoic, or heterogeneous on ultrasound examination, and subcapsular hemorrhage appears as a perirenal fluid collection that flattens the underlying renal contour (Fig. 1).

Fig 1: Ultrasound of a 61-year-old male patient. A sagittal view of the right kidney,...

The technical limitations of ultrasound are considerable in further evaluation of these findings, and a CT scan will be performed almost invariably.

• CT

On unenhanced CT, a subcapsular hematoma will appear as a spontaneously dense fluid collection limited by the renal capsule that flattens the underlying renal contour, similar to ultrasound (Fig. 2).

Fig 2: Spontaneous renal hemorrhage. (A) Axial and (B) coronal portal venous phase CT...

The primary source of hemorrhage may be difficult to assess on an initial non-contrast CT since the bleeding can obscure small masses and ruptured cysts. Other causes, such as aneurysms, will also be occult without contrast.

Even on a contrast-enhanced CT, the mass can still be unseen by blending with the adjacent enhancing parenchyma on a single-phase study such as a CT angiogram, the most ordered exam in the suspicion of hemorrhage.

Since masses are the most frequent cause of WS, a multi-phase renal protocol CT is preferred over a CT angiogram. The optimal protocol should include an unenhanced phase, an arterial phase to access the vascular injury, a nephrographic phase to evaluate renal parenchymal lesions, and a delayed phase to evaluate bleeding and collecting system injuries.

Some CT signs should help locate whether there is active bleeding and point to the site of hemorrhage.

The sentinel cloth sign relies on the higher density of sub-acute blood (60 HU) compared to acute blood (35-45 HU) on an unenhanced CT and can hint at the location of the bleeding site. Signs like contrast extravasation or blushing in the arterial and nephrographic phases indicate active bleeding.

Etiology

• Neoplastic

• • Angiomyolipoma:

Angiomyolipoma (AML) is the most common benign solid renal mass and is typically discovered incidentally.

Usually sporadic, it has a female predominance and higher frequency in tuberous sclerosis, von Hippel-Lindau disease, and neurofibromatosis type 1.  

AML remains the most frequent cause of WS and accounts for nearly 30% of reported cases.

The composition of an AML is, as the name implies, a mixture of vascular, smooth muscle, and adipose tissue in varying proportions. Because of these differences in composition, its appearance varies. The predominant difference is the fat content. Typically, it demonstrates macroscopic fat (less than -20 HU), but in 5% of cases, AML is lipid-poor, making it more challenging to differentiate from a clear cell renal cell carcinoma (ccRCC).

Tumor size and vascularity are predictors of bleeding. Patients with lesions larger than 4 cm and aneurysms greater than 5 mm are at greater risk.

Fig 3: Axial non-enhanced CT (A), enhanced arterial phase (B), and portal venous phase...

Fig 4: Left kidney digital subtraction angiogram (A) of the same patient as in the...

• • Renal Cell Carcinoma:

Renal cell carcinoma (RCC) is the most common malignant epithelial tumor, accounting for approximately 90% of all solid renal tumors in adults. It is also the most common malignant tumor known to cause WS.

RCC includes a heterogeneous set of tumors with different histological and imaging findings and prognoses.

The main two subtypes are clear cell and papillary tumors. ccRCC is much more likely to bleed than the papillary subtype, owing to its nature, characterized by neovascularity and necrosis from fast tumor size progression. Imaging is usually helpful in differentiating these two subtypes, although it may be difficult to distinguish in the acute setting of hemorrhage.

Additionally, the differential between ccRCC and AML is even more challenging, especially in the context of WS. An MRI study after the initial evaluation of WS is helpful, as CT may be unsatisfactory.

Unlike AMLs, ccRCC are known to bleed at any size.

Fig 5: Ultrasound of a 76-year-old male patient, (A) coronal and (B) sagittal views of...

Fig 6: One year later, the same patient in the previous figure was admitted with left...

• Vascular

Vascular disease is classically the second most common condition predisposing to WS, after both benign and malignant neoplasms. However, a recent systematic review of the literature reported that the whole group of malignant neoplasms (14.7%) is less common than vascular disease (25.5%) as a causative etiology for WS.

Among vascular diseases, polyarteritis nodosa (PAN) is the most common (11.8%). It has surpassed ccRCC (6.9%), becoming second only to AML. This fact is probably due to the growing number of incidentally diagnosed small malignant renal neoplasms, leading to earlier treatment and avoiding significant growth that results in WS.

• • Polyarteritis nodosa

PAN is a systemic necrotizing vasculitis affecting both small and medium arteries, frequently involving the kidneys (80%), only behind cutaneous and peripheral nerve involvement.

Aneurysms occur in the context of vascular injury and necrosis, which lead to hemorrhage from ruptured microaneurysms in the interlobar arteries and arcuate arteries. Another outcome of vascular injury is thrombosis, leading to focal parenchymatous infarctions.

CT findings include enlarged kidneys, often with wedge-shaped areas of parenchymal hypoenhancement.

Fig 7: A 51-year-old female patient with a diagnosis of polyarteritis nodosa (PAN) was...

Fig 8: The same patient with polyarteritis nodosa (PAN) in the previous figure is...

Fig 9: A digital subtraction angiogram of a different patient with polyarteritis...

Other known WS causes of vascular nature are granulomatosis with polyangiitis and systemic lupus erythematosus (SLE). WS related to SLE occurs due to renal vein thrombosis, and the same can be seen with hypercoagulable states.

Lastly, spontaneous arteriovenous fistulae are rare, but in case of rupture can also lead to parenchymal hemorrhage with perirenal extension.

• Infection

Infection, both acute and chronic, can lead to WS. Bleeding is more common in severe infections and in individuals with diabetes. The cause of hemorrhage is not fully understood, but it is believed to be linked to parenchymal damage and erosion of blood vessels.

Fig 10: An 86-year-old male patient with a recent history of urinary sepsis was...

• Cystic Renal Disease

• • Acquired renal cysts

A “renal cyst” is a term often used to refer to any cystic lesion in the kidney. Benign epithelial cysts are prevalent, mostly in people over 50, and are found in about 40% of individuals who have a CT scan. Most benign kidney cysts do not cause symptoms, but they may rupture and cause pain in rare cases. Infrequently, they may also be the underlying cause of WS.

Fig 11: A 61-year-old male patient was admitted with complaints of left flank pain and...

• • Acquired cystic kidney disease

Renal atrophy and cystic disease are common in long-term hemodialysis patients, and the number of cysts increases over time. Spontaneous bleeding in these patients has been reported as early as 1971. It can be caused by two main factors, calcified blood vessels and weak vessels in the walls of cysts. The bleeding can occur within a single cyst, but it is more often widespread, with subcapsular hematoma and perirenal hemorrhage.

Fig 12: A 38-year-old male patient with hypertension and end-stage renal disease who...

• Oral anticoagulation therapy/coagulation disorders

Hemorrhage, in these cases, often occurs in multiple areas of the abdomen, such as the abdominal wall and retroperitoneum. It tends to be larger in volume and more widespread than hemorrhage caused by ruptured neoplasms or vascular disease, which are usually more localized.

A characteristic sign of this type of bleeding is the hematocrit sign. It consists of a cellular-fluid level in the dependent portion of the hematoma by settling cellular elements. This is a highly sensitive sign of coagulopathy or oral anticoagulant therapy and has been reported to be present in 87% of cases.

Fig 13: An 83-year-old female patient with atrial fibrillation on oral anticoagulants...

Treatment

The management of bleeding depends on its cause, whether there is active bleeding and the patient's hemodynamic status. Conservative therapy consists of fluid and blood product resuscitation, reversal of anticoagulation, and treatment of underlying conditions.

In the past, surgery was often used to treat hemorrhage. However, the nature of the condition dictated that in most cases nephrectomy of partial nephrectomy was needed. It is now reserved for unstable patients or when malignancy has been identified as the cause of bleeding.

More recently, interventional radiology, such as angiography and transarterial embolization, is the preferred approach. Embolization has been shown to be safe and effective for both initial and recurrent bleeds, avoiding unnecessary nephrectomy in bleeding caused by benign conditions.