Teaching Case

A 16-year-old male presented to our Ultrasound division with right sided ureteric colic in Jun 2020.

A right ureterovesical junction calculus was detected and a 6cm x 6cm rounded well-circumscribed hypoechoic mass with through-transmission was found in the pancreatic tail with no peripancreatic fluid collection and normal pancreatic head and body. CT scan of the abdomen revealed a well-defined isodense lesion with regular margins in the tail of the pancreas measuring 5.4(TR) x 5.1(AP) x 3.8(CC) cm. No intralesional calcification or dilated main pancreatic duct was noted. It had well-maintained fat planes with the adjacent crus of diaphragm, left adrenal gland, spleen, left kidney and left para aortic region, compressing the splenic vessels with multiple perigastric and splenic hilar collaterals. Minimal post contrast enhancement with non-enhancing hypodense central areas was seen. MRI revealed T1WI isointense signals with T2 hyperintense cystic areas within, diffuse restriction on DWI with low ADC values and normal pancreatic duct. Post Gadolinium injection, heterogeneous peripheral enhancement with non-enhancing hypointense central areas was noted.

Solid pseudopapillary neoplasm is a rare exocrine pancreatic neoplasm, accounting for 1-2.7% of all pancreatic tumors, predominantly found in young women, first described by Virginia Frantz in 1959 [5]. It was variously named ‘Frantz tumor’, ‘Hamoudi tumor’, papillary epithelial neoplasm, solid and papillary tumors (SPT), till WHO classified it as Solid Pseudopapillary Neoplasm (SPN) in 1996 [1,2]and as low grade malignant neoplasms in 2010 [6,7,8]. An indolent neoplasm, with 85-90% female preponderance, it presents in the second to third decades in women and at a later age in men with peak incidence at around 64 years of age [3, 4]. SPN’s have been diagnosed more and more as the number of imaging tests increase globally [1,9]. Male SPN’s are more likely to show aggressive features, and to metastasize [10].  The majority present with abdominal discomfort and pain (68%) and 38% are diagnosed incidentally. Upto 15% are malignant and may be unresectable if presenting late [3, 10, 11]. 95% 5-year survival rates after resection, even in cases with aggressive behaviour () [3,6,7,9,10], make it essential to know their imaging features.

The tumours may be small (<3 cm) or large (>3 cm) [3].  Ultrasound features consist of a well-defined heterogeneous mass due to solid and cystic components. CT imaging usually demonstrates a well encapsulated lesion with varying solid and cystic components owing to haemorrhagic degeneration with calcification in some. Post- contrast features include enhancing solid areas peripherally, with central cystic spaces. Metastatic deposits in liver and lymphnodes, if present, show similar characteristics [11, 12]. MRI typically shows a well-marginated, encapsulated, solid and cystic mass with areas of haemorrhagic degeneration (high signal intensity on T1- weighted imaging) and progressive peripheral or heterogeneous contrast enhancement, after gadolinium administration. Small tumours (<3 cm) may be homogeneous and hypo to isoattenuating on CT, and may not show high signal on T1WI on MRI, owing to lack of cystic component, calcification and haemorrhage in these [3].

In our case, the absence of typical features posed a diagnostic dilemma ,i.e. a young male, with a large tumour, but no calcification on CT or haemorrhage on MRI. However, its typical location, the absence of mass effect and well-encapsulated cystic nature led us to a provisional diagnosis of SPN, later confirmed on post-surgery histopathology. This case highlights an atypical clinical and imaging presentation of an incidentally detected rare pancreatic tumour. It is important to keep SPN in mind as a differential, as it can show aggressive features and even metastasize, especially in men