Teaching Case

We report the case of a 67-year-old asymptomatic male patient who performed a routine follow-up enhanced abdominal and pelvic CT examination after undergoing a radical left nephrectomy 5 years earlier, at another institution, due to a left renal cell carcinoma. Physical examination and laboratory examinations were unremarkable.

CT revealed an incisional left superior lumbar hernia just below the spleen, an uncommon finding in itself, containing large bowel, fat and a well-circumscribed rounded nodule measuring 13x10mm (arrow in Fig.1a and b). This nodule showed a homogenous enhancement pattern in the venous portal phase (Fig. 1a) similar to that of the spleen (Fig.2). Comparative analysis of regions of interest of both the nodule and the spleen during venous portal phase enhancement revealed a matching density (Fig.3). A vascular pedicle could also be traced to the splenic hilum, arising from the splenic artery (arrow in Fig.4). After comparison with previous enhanced CT performed annually over the last 2 years (Fig.5 and Fig.6), this nodule remained unchanged inside the lumbar hernia, in keeping with a herniated accessory spleen.

Accessory spleens, or splenunculi, are congenital foci of ectopic splenic tissue that are separate from the main splenic body [1]. They are found in up to 16% of the general population [2], representing the most common of all splenic anomalies [3]. Most are found around the splenic hilum, along the splenic vessels or the splenogastric ligament, in the omentum, the mesentery, the left broad ligament (in females) or the left spermatic cord (in males) [4].

They result from incomplete fusion of splenic tissue around the fifth week of gestation. Since the spleen is formed in the dorsal mesogastrium and later rotates to the left side, accessory spleens are always located on the left side of the abdomen [5]. It is uncommon to find accessory splenic tissue in more than two locations [6].

They most commonly present as incidental asymptomatic findings [7]. They typically appear as well-circumscribed, rounded masses smaller than 2cm which enhance homogeneously after contrast administration [7].

Supplying vascular branches arising from the splenic artery have been reported in about 43.3% of cases in enhanced CT evaluation [5]. Our patient had a fairly long vascular pedicle, which was probably a predisposing factor for herniation.

To our knowledge, this is the 3rd case of a herniated accessory spleen described in literature, and the first one of a herniated spleen inside a lumbar hernia. In 1993 Tomioka and Nakajima reported a case of a Bochdalek hernia with an intrathoracic accessory spleen [8] and in 1999 Ohta et al. described a case of a diaphragm hernia containing an accessory spleen [9].

Clinical importance of accessory spleens arises either when a splenectomy is being considered of if spontaneous torsion occurs (extremely rare).

In our case, detecting and reporting the herniated accessory spleen was of vital importance as to raise the surgeon’s awareness in the event of a hernia repair. This unusual location and the presence of herniated large bowel could also, in theory, due to extrinsic pressure, increase the risk of torsion. Awareness of its presence is also important in the event of removal of all functional splenic tissue as in cases of haematologic diseases[7].

In this case the differential diagnosis with lymphadenopathy or a peritoneal implant had to be considered. Besides there being no evidence of local or distant tumour recurrence, other factors such as location, stability, enhancement pattern, density equal to that of the spleen and a visible vascular pedicle arising from the splenic artery made for the confident diagnosis of a herniated accessory spleen.