Ⅱ.
Ectopic tissues in the abdomen
1. Ectopic pancreas
Ectopic pancreas refers to pancreatic tissue without connection to the body of the pancreas.
The most common location of the ectopic pancreas is the stomach,
followed by the duodenum and jejunum,
and these locations account for more than 70% of cases (1).
In the stomach,
the antrum is most commonly affected.
Less common locations for ectopic pancreas include the ileum,
Meckel’s diverticulum,
gallbladder,
bile ducts,
splenic hilum,
umbilicus,
fallopian tubes,
mediastinum,
esophagus,
lymph nodes,
and omentum (1).
On gastrointestinal endoscopy,
ectopic pancreas usually appears as an incidental submucosal tumor in the stomach or duodenum ( Fig. 1 ).
The recognition of the orifice of the pancreatic duct can be an important finding to suspect this condition.
On either ultrasonography (US) or CT,
ectopic pancreas in the stomach and duodenum is typically depicted as a submucosal ill-defined mass ( Fig. 1 ).
Ectopic pancreas in the small bowel often shows lobulated contour,
similar to normal pancreas ( Fig. 2 ).
Contrast-enhanced CT,
especially with dynamic enhancement,
is beneficial in demonstrating intense enhancement.
Occasionally,
ectopic pancreas may be associated with cyst formation ( Fig. 2 ),
resulting from focal pancreatitis.
Rarely,
it may be complicated by the development of adenocarcinoma ( Fig. 3 ).
MRI is also a useful modality for demonstrating peculiar signal pattern in pancreatic tissue,
which is typically high signal intensity on T1-weighted and low signal intensity on T2-weighted images ( Fig. 2 ).
MRCP may also be useful for demonstrating the pancreatic duct in ectopic pancreas,
which is pathognomonic for this condition ( Fig. 2 ) (1).
Fig. 1: Ectopic pancreas associated with pseudocyst in a 10-year-old boy, who presented with acute upper abdominal pain.
(A) Contrast-enhanced CT shows an irregular-shaped mass containing a cystic area (arrow) in the posterior wall of the gastric antrum.
(B) Coronally reformatted image of the CT image shows a submucosal cystic mass (arrow).
(C) Upper gastrointestinal endoscopy demonstrates a submucosal tumor (arrowheads) associated with an orifice (arrow), suggesting the diagnosis of ectopic pancreas.
(D) Microphotograph of the surgical specimen shows pancreatic tissue (arrows) beneath the gastric mucosa (low power view of HE stain).
Fig. 2: Ectopic pancreas in the proximal jejunum in a 66-year-old man.
(A) Contrast-enhanced CT shows an irregular shaped ectopic pancreas (arrow) adjacent to the proximal jejunum. Note a similar degree of enhancement in both the pancreatic uncus (arrowhead) and ectopic pancreas.
(B) T1-weighted gradient MR image with fat suppression shows similar high intensity in the ectopic pancreas and the pancreatic uncus.
(C) T2-weighted fast spin-echo image shows similar decreased intensity in the ectopic pancreas and the pancreatic uncus.
(D) Magnified image of the previous image (C) shows a pancreatic duct (arrow) in the ectopic pancreas (arrow).
Fig. 3: Adenocarcinoma arising from ectopic pancreas in the gastric antrum in a 52-year-old woman, who presented with loss of appetite.
(A) Contrast-enhanced CT shows an area (arrow) showing intense enhancement in the gastric antrum.
(B) Gastrointestinal endoscopy shows a submucosal tumor (arrowheads) in the gastric antrum. Note the deformed pyloric ring (arrow)
(C) Microphotograph of the surgical specimen shows infiltrating adenocarcinoma (arrows) adjacent to the focus of ectopic pancreatic tissue (arrowheads). Immunohistochemistry also confirmed pancreas origin of the adenocarcinoma (not shown)
(low power view of HE stain).
2. Accessory spleen / Wandering spleen / Splenosis / Polysplenia
Abnormally located spleen includes accessory spleen,
wandering spleen,
splenosis,
and polysplenia.
Accessory spleen is congenital migration of splenic tissue,
and its incidence is estimated between 10% and 30% (2).
The most common location is the splenic hilum,
followed by the pancreas tail.
The less common locations include the omentum,
mesentery,
small intestinal wall,
female adnexa,
and scrotum (2).
On unenhanced CT,
accessory spleen is a well-defined and usually solitary,
round nodule,
with a mean diameter of 12mm (3).
Contrast-enhanced CT is useful in comparing the degree of enhancement between accessory and normal spleen.
The acquisition of arterial phase allows the recognition of increased enhancement ( Fig. 4 ) (3).
Accessory spleen in the pancreas tail ( Fig. 4 ) should be carefully distinguished from hypervascular pancreatic tumors such as neuroendocrine tumors,
and it may be complicated by epidermoid cyst ( Fig. 5 ).
MRI is another modality of choice for comparing the signal intensity in suspected accessory spleen and normal spleen with a variety of MR sequences ( Fig. 4 ).
When splenectomy is performed,
accessory spleens undergo compensatory enlargement ( Fig. 6 ),
and they should not be confused with neoplastic conditions.
Fig. 4: Accessory spleen in pancreas tail in a 47-year-old man.
Arterial (A) and venous (B) phase of dynamic contrast-enhanced CT show a nodule in the pancreas tail (arrow), which shows a similar degree of enhancement to the spleen (arrowheads).
Fat-suppressed T2-weighted MR image (C) and diffusion-weighted image (D) also successfully demonstrate the similar intensity between the pancreatic nodule and spleen.
Fig. 5: Epidermoid cyst in an accessory spleen of the pancreas tail, in a 67-year-old woman.
Contrast-enhanced CT shows a well-demarcated cystic lesion (arrows) in the pancreas tail.
Fig. 6: Figure 6-1. Accessory spleen in a 59-year-old male.
Arterial (A) and venous (B) phase of dynamic contrast-enhanced CT show similar degree of enhancement between an accessory spleen (arrow) and the normal spleen (arrowheads).
Figure 6-2. Enlargement of accessory spleens after splenectomy for splenomegaly in the same patient.
Contrast-enhanced CT obtained at one month after splenectomy shows enlargement of the accessory spleens (arrows).
Wandering spleen refers to splenic migration from its normal position commonly into the pelvic cavity,
and is considered to be derived from incomplete development or laxity of the surrounding ligaments.
This condition is most common in middle-aged women.
The diagnostic CT findings include a homogenous mass with its hilum contiguous to the splenic artery and vein,
and the absence of the spleen in its normal position ( Fig. 7 ).
When wandering spleen is complicated by torsion,
contrast-enhanced CT is useful for demonstrating the lack of enhancement in wandering spleen and a whirled appearance of the splenic vessels ( Fig. 7 ).
Fig. 7: Figure 7-1. Wandering spleen in a 67-year-old woman.
(A) Unenhanced CT of the lower abdomen shows a well-demarcated mass of homogeneous attenuation. Note the presence of an artery and a vein (arrows) in its hilum. The serial images (not shown) confirmed that these vessels represent the splenic artery and vein.
(B) Contrast-enhanced CT of the upper abdomen shows the absence of the spleen in the left upper quadrant. The irregular shaped liver suggests cirrhosis. Dilated vessels (arrows) around the stomach represent secondary gastric varices.
Figure 7-2. Torsion of the wandering spleen in the same patient, who presents with acute abdominal pain of sudden onset.
Contrast-enhanced CT obtained at one-year after the previous CT images demonstrates poor enhancement in the wandering spleen, suggesting the diagnosis of torsion.
Splenosis is autotransplantation of splenic tissue,
usually after splenic trauma or surgery.
The common locations include the omentum,
intestinal serosa,
parietal peritoneum,
and undersurface of the diaphragm.
Thoracoabdominal injury may lead to thoracic splenosis.
In contrast to accessory spleens,
splenosis nodules tend to be numerous and irregular-shaped without the hilum or capsule ( Fig. 8 ).
Although imaging features in this condition may simulate peritoneal neoplastic conditions,
the identification of the previous history of splenic trauma and/or splenic surgery helps diagnose this condition.
Fig. 8: Splenosis in an asymptomatic 62-year-old man with a previous history of splenectomy due to traffic accident.
(A) Unenhanced CT shows a nodule in the Morrison’s pouch (arrow).
(B) Unenhanced CT at a lower level shows another nodule (arrow) in the omentum.
He has a history of undergoing exploratory laparotomy for evaluation of these masses. At surgery, numerous splenosis nodules were found in the peritoneal cavity.
Polysplenia is a congenital anomaly with multiple masses of splenic tissue,
typically associated with situs ambiguus and cardiovascular anomalies (4).
On either CT or MR imaging,
anomalous splenic masses of variable size and number show similar appearance to normal spleen typically in the upper abdomen ( Fig. 9 ) (4).
Fig. 9: Polysplenia in a 27-year-old woman with a history of ventricular septal defect repair, who presented with leg edema.
Arterial phase image of dynamic contrast-enhanced CT shows heterogeneous enhancement of round masses (arrows) in the right upper quadrant. This enhancement on early phase is similar to normal spleen. Mirror imaging position of the liver and stomach (arrowhead) is seen as a part of situs ambiguus, which is often associated with polysplenia.
3. Ectopic gallbladder
Gallbladder (GB) can be ectopically located in a wide variety of conditions. The most common GB ectopia is left-sided GB,
which may occur in association with portal vein anomaly.
In this condition,
the umbilical portion of the portal vein moves to the right and the right anterior segmental portal vein diverges from the deviated umbilical portion,
whereas the posterior segmental portal vein diverges from the main trunk.
These anomalies of the portal vein are the diagnostic clues for this condition ( Fig. 10 ) (5).
The second most common GB ectopia is floating GB,
in which GB does not attach to the inferior surface of the liver.
In old women,
this condition has propensity for torsion.
The recognition of the enlarged floating GB and the twisted pedicle on CT is the key to the diagnosis ( Fig. 11 ).
Suprahepatic GB,
resulting from the atrophy of the right anterior hepatic lobe,
may be encountered in patients with cirrhosis ( Fig. 12 ) (6).
Other less common locations include the retro- and intrahepatic,
retroperitoneal regions,
within the lesser omentum,
and within the falciform ligament (6).
Fig. 10: Left-sided gallbladder associated with anomalous portal system in a 61-year-old man.
(A) Contrast enhanced CT shows anomalously located gallbladder (arrow), left side to the falciform ligament (arrowhead).
(B) CT image at the level of the hepatic hilum shows displacement of the umbilical portion (arrow) of the portal vein to the right side of the quadrate lobe of the liver.
(C) CT image at the level 1cm lower than (B) shows the anterior segmental portal vein (arrow) ramifies from the ventral portion of the umbilical portion and the posterior segmental portal vein (arrowhead) ramifies from the main trunk of the portal vein.
Fig. 11: Gallbladder torsion in a 97-year-old woman, who presented with acute abdominal pain of sudden onset.
(A) Contrast-enhanced CT of the upper abdomen shows decreased enhancement in the wall of the markedly enlarged gallbladder (arrows).
(B) CT image at a higher level shows a whirled appearance of the gallbladder neck (arrow).
Subsequent surgery confirmed twisted gallbladder with hemorrhagic necrosis.
Fig. 12: Suprahepatic gallbladder in a 69-year-old man with cirrhotic liver.
Contrast-enhanced CT of the subphrenic region shows the gallbladder (arrow) cephalad to the liver. Note marked atrophy of the right anterior lobe of the liver.
4. Ectopic liver / Accessory lobe of the liver
Ectopic liver is liver tissue that is separate from the liver (7),
and is usually an incidentally found small mass during autopsy and laparoscopy (8).
In a large autopsy series,
the incidence was reported as 0.23% (13/5500) (8).
The most common location is on the surface of the gallbladder.
Other known locations include the gastrohepatic ligament,
umbilical cord,
adrenal glands,
splenic capsule,
pancreas,
and thoracic cavity (8).
Ectopic liver has tendency to be complicated by the development of hepatocellular carcinoma,
which may be explained by anomalous blood supply and biliary drainage.
On CT,
hepatocellular carcinoma in ectopic liver is depicted as a lobulated,
heterogeneous mass with increased vascularity on arterial phase image of dynamic contrast CT ( Fig. 13 ).
Accessory lobe of the liver is abnormally positioned liver tissue that is attached to the liver directly or with a stalk ( Fig. 14 ) (7).
Fig. 13: Hepatocellular carcinoma (HCC) arising from an ectopic liver in a 70-year-old man.
Contrast-enhanced CT (A) and coronally reformatted image (B) show a heterogeneously enhanced mass (arrows) between the stomach and spleen. Post-surgical pathology yielded HCC arising from an ectopic liver. (Case courtesy of Yasuhisa Kurata, MD)
References: Department of diagnostic radiology, Kobe city medical center general hospital - Kobe/JP
Fig. 14: Accessory lobe of the liver in a 59-year-old man.
Contrast-enhanced CT shows an accessory lobe (arrows) contiguous to the caudate lobe of the liver, with a similar degree of enhancement.
5. Ectopic kidney / supernumerary kidney
Ectopic kidney is a condition caused by congenital migration of the mesonephric buds,
and commonly found as pelvic kidney or crossed renal ectopia (9).
These ectopic kidneys are prone to renal injury,
calculus formation,
hydronephrosis,
and infection.
Supernumerary kidney refers to an accessory kidney with its own collecting system,
blood supply and capsule,
regardless of a connection to normal kidney,
and is one of the rarest of congenital renal anomalies.
It is usually found in the abdomen caudal to the ipsilateral kidney.
On imaging studies,
the detection of the characteristic shape of the kidney and the presence of the ureter are pathognomonic for these ectopically located kidneys ( Fig. 15 ).
Fig. 15: Pelvic kidney incidentally found in an 18-year-old man.
Contrast-enhanced CT of the pelvis shows a prominently enhanced mass exhibiting a peculiar shape of the kidney.
6. Ectopic adrenal tissue
Ectopic adrenal tissue,
also known as adrenal rest tissue,
refers to adrenal tissue outside the normal adrenal gland.
Since the adrenal primordium closely located to the urogenital primordium,
ectopic adrenal tissue is usually found near the adrenal gland or along the path of gonadal descent (10).
Ectopic adrenal tissues have been reported in other sites including the retroperitoneum,
broad ligament,
ovary,
testis,
thorax and spinal region (10).
Adrenal rest tissue may be complicated by the secondary development of a distinct benign tumor,
especially in the liver and testis.
Hepatic adrenal rest tumor is typically located in the subcapsular region of the right posterior lobe and shows increased vascularity on arterial phase of dynamic CT ( Fig. 16 ).
Chemical-shift MR imaging is also beneficial for demonstrating microscopic fat.
Testicular adrenal rest tumor is often seen in patients with congenital adrenal hyperplasia (CAH).
CAH is an autosomal recessive disease caused by a defect of enzyme mediating cortisol production.
Testicular adrenal rest tumor may cause male infertility in patients with CAH.
Fig. 16: Adrenal rest tumor in the posterior lobe of the liver, incidentally discovered in a 70-year-old woman.
(A) Arterial phase contrast-enhanced CT shows a hypervascular mass (arrow) of the posterior hepatic lobe in the subcapsular region.
(B) Microphotograph of the pathologic specimen obtained via core-needle biopsy shows benign adenomatous adrenal cells, composed of abundant eosinophilic and occasional foamy cytoplasm (arrows).
7. Cryptorchidism
Extrascrotal location of the testis is well known as cryptorchidism,
resulting from incomplete descent of the testis,
and is one of the most common congenital anomalies.
Undescended testis is usually found along the line of testicular descent between the abdomen and scrotum. Unusual locations include the perineum,
contralateral scrotum,
femoral canal,
and abdominal wall.
Undescended testis shows complete atrophy in 15% to 40% of cases and is called vanishing testis (11).
The important clinical issues in cryptorchidism are infertility and secondary germ cell tumors.
A retroperitoneal tumor found in a patient without normal testis is suggestive of germ cell tumor ( Fig. 17 ).
Orchidopexy is usually recommended for cryptorchidism at 6 months of age (11).
Cryptorchidism is usually an isolated finding.
However,
it can occur in association with endocrine abnormalities such as androgen insensitivity syndrome (AIS),
previously called testicular feminization syndrome,
and sexual development disorders such as mixed gonadal dysgenesis (12).
Patients with AIS may show female phenotype and grow up as females,
though they have XY karyotype and the uterus,
cervix,
and proximal vagina are absent (12).
Mixed gonadal dysgenesis is characterized by sex ambiguity and mosaicism 45,X/46,XY,
and the presence of a testis and a streak gonad (13).
Gonadectomy is recommended in both AIS and mixed gonadal dysgenesis because the testes are usually undescended and have propensity to develop secondary germ cell tumors.
In the preoperative assessment,
accurate localization of undescended testis is crucial for determining the surgical procedure.
Diffusion-weighted image (DWI),
in combination with conventional MRI,
is particularly useful ( Fig. 18 ).
On DWI,
undescended testis shows high-signal intensity ( Fig. 19 ).
Fig. 17: Cryptorchidism complicated by secondary seminoma in a 61-year-old man, who presented with rapidly worsening abdominal distension.
(A) Contrast-enhanced CT shows a huge retroperitoneal tumor (arrowheads), displacing the ileum (arrow) anteriorly.
(B) Image at the level of the groin discloses the absence of the right spermatic cord (circle).
Ultrasonography-guided biopsy of the tumor confirmed seminoma.
Fig. 18: Cryptorchidism in a 19-year-old patient with androgen insensitivity syndrome (previously called testicular feminization syndrome).
Coronal T2-weighted MR image demonstrates anomalously located bilateral testes (arrows) in the upper site of the inguinal canal.
(Case courtesy of Ayako Ohno, MD and Giro Todo, MD)
References: Diagnostic radiology, Osaka Red Cross hospital - Osaka/JP
Fig. 19: Cryptorchidism in a 23-year-old patient with mixed gonadal dysgenesis.
Axial fusion image of T2-weighted image overlaid by diffusion-weighted image, b factor 1000, demonstrates high signal intensity in undescended gonads (arrows).
8. Ectopic ovary
Ectopic ovary refers to any ovarian tissue apart from normal ovaries (14),
regardless of the direct connection to the ovary.
Although ectopic ovary is usually asymptomatic,
various ovarian tumors can develop in ectopic ovary.
The ovary can be found in ectopic locations as a result of ovarian developmental maldescent,
malposition during and after the pregnancy,
and autoamputation.
Abnormally located ovaries in these conditions are occasionally also called ectopic ovary.
Incomplete descent of the ovary during the development can lead to an ectopic location of the ovary,
from the lumbar region to the pelvis.
Ovarian malposition occurs during normal pregnancy and it may persist after the delivery because of adhesions.
Autoamputation of the ovary results from torsion.
In autoamputated ovary,
the preoperative diagnosis is challenging,
and the diagnosis is usually established only after laparotomy.
In patients who have a history of pelvic radiation,
the location of the ovaries should be carefully interpreted because the ovaries might be transposed outside the radiation field.
Common sites for the transposition include the paracolic gutters ( Fig. 20 ),
and anterior aspect of the psoas muscles.
Fig. 20: Ovarian transposition in a 32-year-old woman, who underwent ovarian transposition before radiation therapy for cervical cancer.
Contrast-enhanced CT of the lower abdomen shows surgically moved ovaries in the bilateral colic gutters (arrows).
9. Ectopic prostate tissue
Ectopic prostate tissue is most commonly found in the male urethra and the urinary bladder (15).
A urethral lesion presents as a polypoid mass,
called as prostatic-type polyp (16).
Less common sites of ectopic prostatic tissue include the female genitourinary tract,
anal canal,
paracolic gutter,
retroperitoneum,
and spleen (15).
Most cases of ectopic prostate tissue are small,
less than 5mm,
associated with hematuria or detected incidentally (15),
though incidentally found tissue on imaging studies is usually larger.
MRI has an advantage in comparing ectopic prostate to normal prostate on various sequences ( Fig. 21 ).
Fig. 21: Ectopic prostate tissue in a 69-year-old man.
Axial T2-weighted (A), T1-weighted (B), diffusion-weighted (C) image show a mass (arrows) anterior to the prostate gland. The mass exhibits similar intensity to normal prostate gland (arrowheads) on each sequence.(Case courtesy of Ayako Ohno, MD and Giro Todo, MD)
References: Diagnostic radiology, Osaka Red Cross hospital - Osaka/JP
10. Ectopic uterus (anomalous rudimentary horn of the unicornuate uterus)
Rudimentary horn is found in 65% of unicornuate uterus and regarded as a kind of ectopic uterine tissue.
This condition may be associated with renal anomalies ipsilateral to rudimentary horn,
such as renal agenesis,
in 40% of cases.
Rudimentary horn can be solid non-cavitaty (51%),
cavitary without communication to the uterine cavity (34%),
or cavitary with communication (15%) (17).
Unicornuate uterus with cavitary rudimentary horn is associated with high risk of ectopic pregnancy and removal of rudimentary horn may be preferred for preventing ectopic pregnancy.
T2-weighted image of MRI is a useful tool for evaluating the cavitation in trudimentary horn by demonstrating zonal anatomy of the uterus,
with the endometrium of high signal intensity and the junctional zone of distinct low signal intensity ( Fig. 22 ) (18).
Non-cavitary horn is depicted as a homogenous mass with intermediate intensity similar to the outer myometrium (18).
Fig. 22: Ectopic pregnancy in a rudimentary horn of the unicornuate uterus in a 32-year-old woman at 7 weeks' gestation.
(A) Axial T2-weighted image shows a cystic structure (arrows) surrounded by a thick wall (arrowheads) exhibiting the zonal anatomy of the uterine myometrium, which consist of the inner layer showing low signal intensity and the outer layer showing intermediate intensity.
(B) Axial T1-weighted image shows low signal intensity of the wall similar to the contralateral uterine myometrium.
(C) Axial post-contrast T1-weighted image with fat suppression shows marked enhancement of the thick wall similar to the contralateral uterine myometrium.
11. Accessory breast tissue
Accessory breast tissue,
also known as ectopic breast tissue,
refers to residual breast tissue that persists from normal embryogenesis (19).
In the development,
the mammary ridges,
also known as the milk lines,
extend from the axilla to the inguinal region (20).
In the thoracic area,
the mammary ridges persist and become breast tissues,
while in other areas they normally regress (20).
Accessory breast tissue,
which is found in up to 6% of the population,
can occur anywhere along the milk line (19).
Although the axilla is the most common site,
other reported sites include the face,
neck,
shoulder,
flank,
hip,
and thigh. Occasionally,
accessory breast causes milk discharge and local skin irritation,
and may be complicated by the development of carcinoma and fibroadenoma (19).
On US,
accessory breast tissue appears as a lobulated echogenic mass with internal septations.
At post-partum lactation,
accessory breast tissue may present as a rapidly enlarging mass because of milk production,
and is demonstrated as a multilocular cystic tumor on all imaging modalities ( Fig. 23 ).
On MR imaging,
the accumulated fluid may exhibit bright intensity on T2-weighted and slightly high intensity on T1-weighted MR images,
reflecting the fat and protein content in maternal milk ( Fig. 23 ).
Fig. 23: Accessory breast tissue complicated by milk production in a 31-year-old post-partum woman, who presented with a rapidly enlarging left inguinal mass.
(A) Ultrasonography of the left groin shows a multilocular cystic mass.
(B) Unenhanced axial CT demonstrates a lobulated cystic mass (arrows) with septations.
Axial T2-weighted (C) and T1-weighted (D) MR images show a multilocular cystic mass (arrows) of marked high and moderately high intensity, respectively.
Surgical pathology disclosed lactating ectopic breast tissue with extensive mild production.