Intrapancreatic accessory spleen: a misleading diagnosis
- 1Department of Radiology, Portuguese Institute of Oncology of Lisbon, Lisbon, Portugal
- 2Department of Gastroenterology and Hepatology, Hospital Santa Maria, Lisbon, Portugal
- Correspondence to Dr Alexandre Oliveira Ferreira,
Intrapancreatic accessory spleens are congenital malformations that occur in roughly 2% of individuals. Most of them are innocent until found. Lately, there have been a few case reports of intrapancreatic spleen misdiagnosis leading to unnecessary pancreatic surgery. We report the case of a 64-year-old woman who had a hypervascular pancreatic nodule diagnosed on dynamic CT and MRI after an episode of acute pancreatitis. The patient's progress was followed for 18 months, repeated the CT and MRI examinations and an endoscopic ultrasonography with fine needle aspiration was performed. Neoplastic cells were not identified on cytology. Despite the stability of the lesion, a distal pancreatectomy was performed to exclude a neuroendocrinal tumour. An intrapancreatic accessory spleen was ultimately identified on histological examination.
Intrapancreatic accessory spleen is a common congenital defect, with a prevalence of 2% found in an autopsy series of 3000 people.1 It is usually an asymptomatic and benign lesion but it mimics pancreatic malignant tumours. For this reason, it can be a cause of unnecessary surgery as has been recently reported.2 ,3
It is of the utmost importance to be aware of this entity and to know that it is not only frequent but also possible to diagnose by dynamic CT or MRI, without further invasive procedures.
A woman, 64 years old, with a history of hydatid cysts in the liver and lung for which she had been previously submitted to surgery and a parathyroid adenoma already removed by parathyroidectomy.
She had mild acute hepatitis 2 years ago and imaging examinations were performed for routine evaluation. A mass in the tail of the pancreas was incidentally discovered.
CT documented a well-defined nodular lesion, with 1 cm of diameter, on the tail of the pancreas, showing contrast enhancement in the arterial phase (figure 1), and isodense in the venous and delayed phases. The hypervascular features raised the diagnostic hypothesis of a neuroendocrinal tumour of the tail of the pancreas. The MRI (figure 2) showed a solid lesion, with low signal intensity on T1 and high signal intensity on T2-weighted images, with persisting enhancement on the late phases of dynamic MRI study.
To help in the characterisation of this mass, an endoscopic ultrasound (figure 3) with fine needle aspiration (EUS-FNA) biopsy was performed. The cytology and immunohistochemical panel did not show neoplastic cells.
The patient had normal glycaemia, Ca 19.9 (cancer antigen 19.9), CEA (carcinoembryonic antigen) and chromogranin levels.
Imaging findings of a solid hypervascular mass on the pancreatic tail, in a contrast-enhanced CT, may suggest several diagnoses like neuroendocrinal tumours, solid and papillary epithelial neoplasm, pancreatic adenocarcinoma and even metastases.
One must have a high degree of suspicion to think of an intrapancreatic accessory spleen (IPAS) and rely on spleen-like dynamic behaviour on CT or MRI in order to have certainty in the diagnosis and obviate surgery.
In this case, the diagnosis was not considered unequivocal. And most of all, after several procedures and concerns, the patient wanted to be reassured that she had no serious condition and desired a definitive solution.
Despite the lesion being stable for 18 months, the patient underwent a distal pancreatectomy to exclude malignancy.
Outcome and follow-up
Histological examination of the surgical specimen described a brown mass, capsulated, with 12 mm (figure 4), compatible with an accessory spleen.
The patient recovered from surgery without complications and stays symptomatic, as before.
Accessory spleen, also referred to as splenunculi, consists of a common congenital defect, seen in 10–30% of patients, in autopsy.4–6 It results from a failure in the fusion of mesenchymal cells that form the splenic anlage.5 ,7
In the majority of the cases described in the literature, the finding of an IPAS was incidental during an unrelated imaging study and most of them were diagnosed only after surgery, which is performed for suspected pancreatic neoplasia.
An accessory spleen usually poses no clinical problems and no treatment is necessary unless in the case of torsion, haemorrhage, cyst formation or in the presence of haematological disorders, such as idiopathic thrombocytopaenic purpura.
Intrapancreatic accessory spleens are easily misdiagnosed as neuroendocrinal tumours because of their hypervascular appearance, but besides its location on the tail of the pancreas, the key to suspect of IPAS is similar appearance of the lesion to the spleen in different imaging modalities, including ultrasound, CT and MRI on all contrast-enhanced phases.9
The diagnosis can be confirmed using superparamagnetic iron oxide (SPIO)-enhanced MRI, Levovist (Bayer, Berlin, Germany)-enhanced US and scintigraphy using Tc-99m-labelled sulfur colloid or Tc-99 m-labelled heat-damaged red blood cells. The mechanism of these different techniques is essentially the same: trapping of the contrast material by reticuloendotelial cells.
EUS-FNA may reveal a predominance of small lymphocytes with a subset of histiocytes, conspicuous eosinophil and plasma cells and CD8-positive immunostaining of endothelial cells in cellblock sections.12
Thus, it is important to consider the possibility of an accessory spleen when an asymptomatic intrapancreatic mass is incidentally visualised on examination, and the imaging characteristics of the lesion match those of the spleen.
Intrapancreatic accessory spleen is a common congenital defect (2%).
It is usually asymptomatic and benign.
It is a hypervascular nodule that can mimic a pancreatic tumour.
It may be safely diagnosed with careful radiological investigation avoiding unnecessary surgery.
Competing interests None.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.