Teaching Case

6-days history of abdominal pain, more intense in the right lower quadrant, with diarrhoea and fever. The patient presented with tenderness in right lower quadrant and positive right renal Murphy sign.
Laboratory tests showed increased WBC counts and C-reactive protein. BNU and creatinine levels were normal. Urinalysis showed increased white cells.

The ultrasound performed in the ER showed a perinephric collection with signs of presence of air bubbles, and an abdominal and pelvic contrast-enhanced CT examination was performed.
The CT confirmed the presence of an abscess surrounding the entire right kidney with peripheral enhancement and air bubbles. It extended from a dilated, hyperenhancing appendix with a small appendicolith, indicative of acute appendicitis. There was evidence of rupture of the distal third of the appendix. The findings were consistent with a perforated retro-caecal appendicitis resulting in right perinephric abscess. A small right pleural effusion was noted.
A laparotomy was performed and the diagnosis was confirmed. Appendectomy was performed as well as surgical drainage and debridement of the perinephric abscess. After a two-week course of antibiotics there was marked clinical improvement with no symptoms and normalization of the laboratory tests. The CT examination performed 10 days after surgery showed no abscesses.

Appendicitis is the most common abdominal emergency worldwide and is usually managed with low mortality and morbidity, even if perforated. However, there is important variability of presentation, in part due to the variable anatomical position of the appendix that can be retrocaecal in 65%. [1] Retrocaecal appendicitis is usually associated with atypical and confusing signs and symptoms with delay in diagnosis and treatment. Untreated appendicitis with 48h of evolution are associated with a 98% perforation rate. [2] Retroperitoneal abscesses involving psoas muscle, perinephric space or the lateral abdominal wall are rare but serious complications of acute appendicitis, always associated with a perforated retrocaecal appendicitis. [3]
Perinephric abscess often arises from an ascending urinary tract infection, haematogenous seeding or as a complication of abdominal or urological surgery. Rarely it may be a presentation of infectious disorders of the gastrointestinal tract, as in the case we present.
Ultrasound has some value in the first approach of these patients, and can help in determine the extent of the abscess, presence of renal abnormalities and obstruction of collecting system or gastrointestinal pathology. [4] In our case the ultrasound showed the perinephric collection and excluded hydronephrosis and other renal abnormalities.
In retroperitoneal abscess, contrast-enhanced CT is the most effective diagnostic tool helping in the establishment of the diagnosis and evaluation of the extension of the disease and the relationship to adjacent structures. [5, 6] It also helps in the therapeutic decision and surgical planning. [7]
The perinephric space has no natural drainage path and requires either percutaneous or open drainage. Perinephric abscesses are associated with high mortality, especially when drainage and broad-spectrum antibiotics are delayed. [4]
In most cases reported in the literature, as in our case, laparotomy is the choice because appendectomy is usually indicated, although there is some controversy of the necessity of urgent appendectomy in patients with perforation. A conservative management and percutaneous drainage of the abscess is a debated option. [8, 9]
Perinephric abscess is a rare complication of perforated retrocaecal appendicitis. The unspecific signs and symptoms often delay diagnosis and treatment. Especially in children, a right perinephric abscess, particularly with bubbles of gas in the absence of renal pathology, should raise the suspicion of complicated retrocaecal appendicitis. CT is a valuable tool in diagnosing and characterizing the disease. Associated to high mortality, an urgent surgical or percutaneous drainage of the perinephric abscess is mandatory. In addition a prolonged broad-spectrum antibiotic treatment is suggested.