CERVICO-ISTHMIC PREGNANCY

MRI sagittal images of the uterus( T1, T2FS) show a low lying gestational sac containing a fetus with empty uterine cavity above it and a large placenta  surrounding the gestational sac.  The cervix is shortened but shows a closed cervical canal suggesting a cervico-isthmic pregnancy. 

A patient presented in her mid thirties with a first trimester intra-uterine pregnancy having conceived after IVF.  USG showed a fetus with cardiac activity and crown-rump length corresponding to 11 weeks' gestation.  The gestation sac was abnormally low lying with an empty endometrial cavity above it. The cervix was poorly visualized. An MRI was indicated to rule out true cervical pregnancy.

MRI showed a low lying gestation sac with empty endometrial cavity above it. The cervix was shortened with a closed cervical canal and internal os. There was a large low lying placenta surrounding the sac with loss of interface between the placenta and myometrium. The myometrium was thinned out. A diagnosis of cervico-isthmic pregnancy was made with the likelihood of adherent placenta.

CERVICO-ISTHMIC PREGNANCY


INTRODUCTION: A cervico-isthmic pregnancy is an ectopic pregnancy which implants in the isthmus. The isthmus is the region between the cervix and fundus.

It is a rare complication of pregnancy and is often confused with a cervical pregnancy. Distinguishing between these is crucial as a cervical pregnancy is virtually not viable while there are a few reports of cervico-isthmic pregnancies being carried successfully to term. Also, cervical pregnancies are more dangerous and associated with serious risks like haemorrhage, rupture, blood transfusions, hysterectomy etc.

INCIDENCE:
Incidence of cervical pregnancy: 1:1000 to 1:16000.
Cervico-isthmic pregnancies are more common than true cervical pregnancies.

IMAGING FINDINGS:
USG: Typically, ultrasound shows an empty uterine cavity with a low lying pregnancy. It may be confused with true cervical pregnancy. In a true cervical pregnancy, the sac is completely within the cervix.

MRI: shows a  low lying gestation sac with a well preserved and closed cervical canal. It is hence helpful in distinguishing cervical from cervico-isthmic pregnancy.

IMPLICATIONS: Although there are reports of successful cervico-isthmic pregnancies, these pregnacies are also exposed to risks like:

• Spontaneous abortion/ premature delivery
• premature rupture of membranes
• placenta accreta
• postpartum hemorrhage
• hysterectomy
• Uterine rupture if associated with thinned out myometrium

REFERENCES:

1. Oyelese Y, Elliott T B, Asomani N, Hamm R, Napoli L, Lewis KM: Sonography and Magnetic Resonance Imaging in the Diagnosis of Cervico-Isthmic pregnancy. J Ultrasound Med 2003; 22: 981-983
2. Strobelt N, Locatelli A, Ratti M, Ghidini A: Cervico-isthmic pregnancy: a case report, critical appraisal of the diagnostic criteria, and reassessment of the outcome. Acta Obstet Gynecol Scand 2001; 80: 586-588.
3. Jelsema RD, Zuidema L: First trimester diagnosed cervico-isthmic pregnancy resulting in term delivery. Obstet Gynecol 1992; 80: 517-519
4. Wikipedia

RHOMBENCEPHALOSYNAPSIS

Figure 1: Coronal T2 image showing fused dentate nucleus

Figure 2: Coronal T2 weighted image showing typical transverse folia and sulci with fused cerebellar hemispheres

Figure 3: Axial T2WI showing fusion of the interfoliate sulci across midline along with fusion of cerebellar folia.

Figure 4: Axial T2WI showing "keyhole appearanca" of 4th ventricle and midline fusion of cerebellar white matter. Vermis is not seen.

Figure 5: Sagittal T2WI showIng absent primary fissure. There is also slight rounding of the fastgial recess. Note the corpus callosum in a patient of isolated rhombencephalosynapsis.

The above MR was done in an adult patient presenting with mild gait ataxia. Rhombencephalosynapsis was detected in him as an isolated finding.

• Rhombencephalosynapsis is a rare  posterior fossa malformation characterized by aplastic/ hypoplastic cerbellar vermis and fusion of cerebellar hemispheres in the midline.
• It was forst described by Obersteiner in 1914.
• Pathogenesis is related to disturbed cerebellar development between 28 to 41 days of gestation.
• Clinical profile varies and is related to the posterior fossa malformation and associated supratentorial anomalies. It might vary from mild truncal ataxia and normal intelligence to cerebral palsy.
• Isolated rhombencephalosynapsis is less common than rhombencephalosynapsis associated with supratentorial anomalies
• Most cases are reported in infancy or pediatric age group with only few cases reported in adults.

Diagnosis is usually by MRI which is clearly superior to CT in evaluating these patients.

Distinctive radiological features are:
Posterior fossa:

• Agenesis / hypoplastic vermis 
• Absent posterior cerebellar incisura, vallecula
• agenesis or hypogenesis of anterior vermis ( rostral ) with hypoplastic posterior vermis( caudal  nodulus may form
• Midline fusion of cerebellar hemispheres to form a single lobed cerebellum
• Fissures and cerebellar folia are transversely oriented best seen on coronal MRI
• Superior and middle cerebellar peduncles may be fused along with dentate nuclei giving a characeteristic diamond shaped, posteriorly pointing 4th ventricle

Supratentorial anomalies:

• Most common supratentorial anomaly is hydrocephalus with aqueductal stenosis
• Sometimes, there may be fused thalami, fornIces, cerebral peduncles, inferior collicluli with absent septum pellucidum
• Dysgenetic limbic system
• cortical malformatins
• sutural synostosis
• hypoplastic commissures, hypoplastic anterior visual pathway and agenesis of posterior lobe of pituitary gland
• Association with septo-optic dysplasia and holoprosencephaly

 References:

• Mendonca JLF, Natal MRCR, Viana SL et al. Rhombencephalosynapsis: CT and MRI findings. Neurology India;152:118-120, 2004.
• Weerakkody Y, Gaillard F et al. Rhombencephalosynapsis. Radiopaedia.org.
• Blaser SI: Rhombencephalosynapsis. Diagnostic Imaging Brain: First Edition. Amirsys: I-1-30, 2005.

IDIOPATHIC INTRACRANIAL HYPERTENSION

IDIOPATHIC INTRACRANIAL HYPERTENSION:

 Figure 1: showing increased fluid in sheaths surrounding optic nerves along with tortuosity of the sheaths

 Figure 2: showing flattening of posterior sclera

Figure 3: Sagittal T2 WI showing a partially empty sella

The above pictures are of a 35 year old female who presented with headache and progressive visual loss.

MRI of the brain and orbits showed a partially empty sella, dilated/ tortuous optic nerve sheaths along with posterior scleral flattening. 
There was no evidence of an intracranial mass/ space occupying lesion or dural sinus thrombosis.

IDIOPATHIC INTRACRANIAL HYPERTENSION( IIH):
Also called pseudotumor cerebri.
As the name implies,the intracranial pressure is raised with no obvious underlying pathology in the brain.
Most common clinical presentation is an obese female aged 20-40 years with headache( aggravated by Valsalva), papilledema, progressive visual loss, diplopia etc.
MRI reveals a partially empty sella, optic nerve sheath dilatation with vertical tortuosity, optic nerve head protrusion and scleral flattening.
The diagnosis is made after other potential causes of raised intracranial hypertension like dural sinus thrombosis, space occupying lesion are excluded.
Aim of treatment is to prevent visual loss which is a potential danger from chronic papilledema.

REFERENCES:

1.  Suzuki H, Takanashi J, Kobayashi K et al: MR Imaging of Idiopathic Intracranial Hypertension. AJNR 22:196-199, 2011
2. Hingwala DR, Kesavadas C, Thomas B et al: Imaging signs in idiopathic intracranial hypertension: Are these signs seen in secondary intracranial hypertension too? Ann Indian Acad Neurol 16(2):229-233, 2013
3. Castillo M: Idiopathic Intracranial Hypertension. Diagnostic Imaging Brain: First Edition. Amirsys: I-10-36, 2005.

MRI in Spigelian Hernia

T1 weighted images in axial and sagittal plane, T2 FS images in axial plane of an 80 year old male presenting with palpable swelling in the right ventral abdominal wall shows focal herniation of mesenteric / omental fat and vessels through a defect in the right spigelian aponeurosis ( that of the internal oblique and transversus abdominis muscles) inferior to the umbilicus. The hernial sac is covered externally by an intact aponeurosis of the extrenal oblique muscle. There is no herniation of bowel loops through this defect.

• Spigelian Hernia is a hernia through a defect in the aponeurosis of internal oblique and transversus abdominis muscles.
• It is seen seen as a defect in the spigelian aponeurosis  lateral to the rectus muscles, inferior to umbilicus where the sheath is deficient posteriorly.
• The external oblique aponeurosis is intact with the hernial sac lying in interparietal/ intermuscular plane 
• It is named after a Belgian surgeon-anatomist by the name of Adriaan van den Spiegel although it was first described by KLINKOSCH
• Raveenthiran has described the existence of spigelian hernias with cryptorchidism called the Raveenthiran Syndrome

• It is a rare hernia, approx. 1%( range of 0.2 -2%) of ventral hernias.
• It is commoner on the right side in 4th-7th decade of life.
• It is commoner in females with a male to female ratio of approx. 1:1.18.

• It may be congenital or acquired
• It may be entirely asymptomatic. Its clinical significance lies in the fact that the hernial opening is small predisposing the bowel loops to strangulation/ obstruction. Hence, it is importatnt to repair it. The repair is usually straightforward and rarely requires a mesh prosthesis.
• It is difficult to diagnose clinically, especially in obese patients
• Imaging: USG is often used in conjunction with Valsalva's manouvre in real time to demonstrate the hernia. CT is considered optimal especially with oral contrast. The role of MRI is less described in literature being a more expensive modality. However, with the wider availability of MRI and its better anatomical visualization, it may prove useful in preoperative evaluation as in this patient.
• Differentials are ventral hernias, umbilical hernia, hernia thorugh laparoscopy port etc.

REFERENCES:

• Harrison LA, Keeshing CA, Martin NL et al. Abdominal wall hernias: Overview of herniography and correlation with cross-sectional imaging. Radiographics 1995; 15(2):315-22.
• Mittal T, Kumar V, Khullar R et al: Diagnosis and management of Spigelian Hernia: A review of literature and our experience. J. Minimum Access Surgery 2008; 4(4): 95-98
• Raveenthiran V. Congenital spigelian hernia with Cryptorchidism: Probably a new syndrome. Hernia 2005; 9(4):378-80
• Federle MP, Jeffrey, RB, Woodward PJ, Borhani AA. Spigelian Hernia. Diagnostic Imaging Abdomen: Second Edition. Amirsys: II-1, 37,2010

SIMPLE BONE CYST

T1 and STIR coronal and sagittal MR images in a 4 year old child showing a fairly well demarcated expansile septate cystic lesion in the proximal metaphyseal region of right humerus. It displays mild heterogeneity but is largely homogenous.

SIMPLE BONE CYST: 
-90% occur in long bones, most common in proximal humerus
-Metaphyseal expansile cystic lesion
-May contain "fallen fragment" which is  a fractured fragment of bone which moves in dependent part with change in patient position. It is usually seen on x-rays and CT.
-May show fluid-fluid level on CT and MRI
-"Rising bubble sign" : Bubble of gas in non-dependent part of lytic lesion suggestes pathologic fracture. It may be seen on CT and MRI.
-FDG active, may hence mimic metastasis on PET-CT

REFERENCE:
Manaster BJ, Roberts CC, Petersilge CA, Moore S, Hanrahan CJ, Crim J.Diagnostic Imaging Musculoskeletal: Non-traumatic disease. Amirsys.2-206, 2010

Focal dehiscnece of lamina papyracea

Above axial CT images show focal dehiscence / absence of lamina papyracea in the right orbit with herniation of orbital fat into the right ethmoid sinus. The medial rectus muscle on this side is slightly thickened and irregular although it does not herniate through the bony defect.
This was an incidental finding in the above young patient.

Dehiscence of lamina papyracea may be congenital or acquired( post traumatic/ post-surgical).
There may either be a focal bony defect or inward displacement of the the lamina papyracea.
The defect is usually small with focal herniation of orbital fat and/ medial rectus muscle into the ethmoid bulla.
However, there may be herniation of the optic nerve or the entire  globe.

IMPORTANCE: This defect provides a direct route for sinus surgery instruments which can cause orbital injuries like medial rectus muscle laceration, orbital hematoma, orbital fibrosis, perforation of the orbital wall, damage to globe etc. Hence, it should be highlighted to the otolaryngologist to avoid possible complications during FESS( functional endoscopic sinus surgery).
It may also cause mild diplopia.

REFERENCES:
Hoang JK, Eastwood JD, Tebbit CL, Glastonbury CM. Multiplanar sinus CT:A Systematic Approach to Imaging Before Functional Endoscopic Sinus Surgery. AJR; 194:W527-W536
Radiology picture of the day. Dr Ahmed Haroun.

HYDATID CYST OF LIVER-MRI APPEARANCE

FIGURE 1:T2 HASTE-AXIAL

FIGURE 2:T1 FS-AXIAL

FIGURE 3:T2 HASTE- CORONAL

Figures above show multiple twisted linear structures within a large SOL in the right lobe of liver s/o collapsed membranes in a hydatid cyst.

HYDATID CYST OF LIVER:
Hydatid disease is a worldwide zoonosis and is cause by the larval stage of Echinoccoccus tapeworm.
There are two main types of hydatid disease cause by E granulosis and E multilocularis. Disease cause by E granulosus is the more frequently encounterd  hydatid disease in humans.
In the life cycle of E granulosus, Dog or other canine animals are the definitive hist while sheep is the most common intermediate host. Man can sometimes be the intermediate host by acquiring the disease either by contact with definitive host or by consumption of contaminated water or vegetables.
Liver is the most commonly involved organ in man( 75%) followed by lungs( 15%) and other viscera( 10%).
Right lobe is the most frequently affected lobe of liver.

STRUCTURE OF HYDATID CYST:
There are three layers: a)pericyst: composed of modified host cells forming a thick fibrous protective layer; b) middle laminated membrane: which is acellular and aloows the passage of nutrients, alos called the ectocyst; c)inner germinal layer or endocyst which forms the scolices and laminated membranes.

IMAGING: depends on the stage of cyst growth. It may be unilocular, may have daughter vesicles, daughter cysts, partial or complete calcification.
X-rays, Ultrasound, CT and MRI all show the hydatid cyst with variable appearances. Complications of hydatid cyst are also seen on imaging.

On MRI, low signal intensity rim on T2WI is characteristic and is likely to represnt the pericyst.
Daughted cysts are seen as cystic structures attached to the germinal layer and appear hypointense as compared to the intracystic fluid on T1 and hyperintense on T2.
Collapsed parasitic membranes are seen as twisted linear structures.
Rim irregularities are also seen on MRI.
MRI also shows complications like migration through diaphragm( on sagittal sequences)

REFERENCES:
Pedrosa I, Saiz A, Arrazola J et al. Hydatid disease: Radiologic and Pathologic Features and Complications. Radiographics 2000;20:795-817