Cowpers duct syringocele

Axial contrast-enhanced CT (top), axial T2W MRI (middle), and sag T2W with fat-saturation MRI (bottom)
demonstrate an ovoid cystic structure associated with the midline posterior aspect of the bulbous urethra

• The Cowper glands (bulbourethral glands) are paired pea-sized accessory exocrine glands analogous to the Bartholin glands in females
• The main glands lie within the urogenital diaphragm
• The ducts insert into the bulbous urethra  
• Provide lubrication of the urethra and protection of the sperm
• Obstruction of the ducts may result in formation of retention cysts, also referred to as syringoceles
• May be congenital or acquired 
• Most often asymptomatic although when large, may result in urinary obstruction and hematuria
• Categorized as either open or closed 
• Open cysts communicate with the lumen of the urethra and may mimic a urethral diverticulum or even an ectopic ureter
• More likely to cause symptoms of postvoid dribbling, purulent discharge and hematuria
• Closed or imperforate cysts become dilated due to duct obstruction resulting in cyst dilatation and extrinsic mass effect on the bulbar urethra
• More likely to result in obstructive symptoms
• Imaging typically detects a Cowper duct cyst as a unilocular cystic lesion at the posterior or posterolateral aspect of the posterior urethra 
• Open cysts may be opacified during urethrography 
• Closed cysts may appear as a smooth extrinsic filling defect on the ventral wall of the bulbous urethra 
• MRI is useful to exclude solid neoplasms and to detect complications such as hemorrhage or infection
• Symptomatic cases are treated surgically with cyst unroofing. Transperineal ligation of the Cowper gland ducts may be performed in refractory cases

References

1. Shebel HM, Farg HM, Kolokythas O, El-Diasty T. Cysts of the lower male genitourinary tract: embryologic and anatomic considerations and differential diagnosis. Radiographics. 2013 Jul-Aug;33(4):1125-43.
2. Surana S, Elshazly M, Allam A, Jayappa S, AlRefai D. A Case of Giant Cowper's Gland Syringocele in an Adult Male Patient. Case Rep Urol. 2015; 2015:682042.
3. Melquist J, Sharma V, Sciullo D, McCaffrey H, Khan SA. Current diagnosis and management of syringocele: a review. Int Braz J Urol. 2010 Jan-Feb;36(1):3-9.
4. Moskowitz PS, Newton NA, Lebowitz RL. Retention cysts of Cowper's duct. Radiology. 1976 Aug;120(2):377-80.
5. Kickuth R, Laufer U, Pannek J, Kirchner TH, Herbe E, Kirchner J. Cowper's syringocele: diagnosis based on MRI findings. Pediatr Radiol. 2002 Jan;32(1):56-8

Persistent Sciatic Artery

Axial and coronal CT images with intravenous contrast demonstrate a left persistent sciatic artery (long arrows) coursing through the greater sciatic notch and deep to the gluteus maximus muscle. Note the asymmetrically diminutive left external iliac artery (short arrows)

• A persistent sciatic artery (PSA) is a rare vascular anomaly in which the internal iliac artery courses through the greater sciatic notch and in to the thigh
• During embryonic development, the sciatic artery usually involutes as the femoral artery develops
• Recognition of an unusually enlarged internal iliac artery and a diminutive external iliac artery are some clues in diagnosing a PSA
• The PSA course runs close to the sciatic nerve, and can run within the nerve sheath in some cases
• Distally, the PSA runs deep to the gluteus maximus muscle, coursing along the adductor magnus muscle
• Reported in up to 0.03-0.06% of the population and can be bilateral in 20% of cases
• PSA is considered complete when it is the dominant blood supply to the popliteal artery and incomplete with the femoral artery is the dominant blood supply to the popliteal artery
• 5 types have been described:
• type 1 is a complete PSA with a normal femoral artery
• type 2 is a complete PSA with a incompletely developed femoral artery
• type 3 is a incomplete PSA (only the cephalic portion is present) and normal femoral artery
• type 4 is a incomplete PSA (only the caudal portion is present) and normal femoral artery
• type 5 is when the PSA arises from the median sacral artery
• Majority (80%) become symptomatic at some point presenting with intermittent claudication, ischemia, pulsatile mass or neurologic symptoms
• Susceptible to repetitive trauma from sitting and hip flexion/extension
• Results in premature atherosclerosis and aneurysm formation
• Aneurysm found in 48%, and stenosis and occlusion of the PSA in 7% and 9%, respectively

References:

1. Mcquaid M, Gavant ML. Posttraumatic pseudoaneurysm of a persistent sciatic artery. AJR Am J Roentgenol. 1995;164 (6): 1514-5. 
2. Pillet J, Albaret P, Toulemonde JL, Cronier P, Raimbeau G, Chevalier JM. Tronc arteriel ischiopoplite, persistance de l’artere axiale. Bull Assoc Anat 1980;64:109e22.
3. Pillet J, Cronier P, Mercier Ph, Chevalier JM. The ischio popliteal arterial trunk: a report of two cases. Anat Clin 1982; 3:329e31. 
4. Gauffre S, Lasjaunias P, Zerah M. Sciatic artery: a case, review of literature and attempt of systematization. Surg Radiol Anat 1994;16(1):105e9.
5. Bower EB, Smullens SN, Parke WW. Clinical aspect of persis- tent sciatic artery: report of two cases and review of the literature. Surgery 1977;81(5):588e95.

Dilated Cisterna Chyli: A Potential Mimicker of Lymphadenopathy

  

Axial (top) and coronal (bottom) contrast-enhanced CT images
demonstrate a retrocrural fluid-filled tubular structure with imperceptible walls
 (black arrows), the classic imaging features of a cisterna chyli

Coronal T2-weighted MRI shows the tubular cystic structure of the cisterna chili
and it's continuity with the thoracic duct (white arrow)

• The cistern chyli is a dilated lymphatic sac ommonly located in the right retrocrural region, at the level of L1-L2, extending 5-7 cm in CC dimension. It classically receives draining lymph from two lumbar trunks and an intestinal trunk, and continues cephalad as the thoracic duct

• Can enhance on delayed MRI >5 min

• Has an average size of 7.4 mm in the AP dimension, although some authors consider it dilated when ≥6 mm

• Dilatation can be secondary to lymphatic damage from prior gastroesophageal or retroperitoneal surgery, uncompensated cirrhosis, hypoalbuminemia, lymphangioleiomyomatosis, elevated central venous pressure, and biliary obstruction

• Size changes can vary depending on phase of respiration, hydration, and lower thoracic duct peristalsis

• Important to know of this entity because it can mimic retrocrural lymphadenopathy in the oncologic setting

• Mulitplanar reformations and MRI can help demontrsate the tubular cystic nature of the cistern chyli and its continuity with the thoracic duct 

References 

1. Rosenberger A, Abrams HL (1971) Radiology of the thoracic duct.Am J Roentgenol Radium Ther Nucl Med 111:807–820
2. Pinto PS, Sirlin CB, Andrade-Barreto OA, et al. (2004) Cisternachyli at routine abdominal MR imaging: a normal anatomicstructure in the retrocrural space. Radiographics 24(3):809–817 
3. Smith TR, Grigoropoulos J (2002) The cisterna chili: incidence and characteristics on CT. Clin Imaging 26:18–22
4. Arrive ́ L, Azizi L, Lewin M, et al. (2007) MR lymphography ofabdominal and retroperitoneal lymphatic vessels. AJR189(5):1051–1058
5. Gollub MJ, Castellino RA (1996) The cisterna chyli: a potentialmimic of retrocrural lymphadenopathy on CT scans. Radiology199(2):477–480 

Re

The axillary nerve and adhesive capsulitis

The axillary nerve (yellow arrow) and the posterior humeral circumflex artery (red arrow) in the region of the quadrilateral space. Note proximity to the inferior capsule.

The axillary nerve is closely related to the inferior capsule of the shoulder. It passes inferior to the subscapularis muscle and travels adjacent to the capsule before entering the quadrilateral space.

The axillary nerve is associated with adhesive capsulitis in at least 2 ways.

First, the axillary nerve can be irritated in the setting of inflammation and thickening of the inferior capsule. The evidence for this is somewhat anecdotal, but makes anatomic sense. The image below is from a patient with adhesive capsulitis. Note the teres minor atrophy (green arrow) in the setting of thickening of the inferior capsule (blue arrow), and constrained fluid in the joint (orange arrow) being forced into the superior subscapularis recess (orange*). The bone lesions are from myeloma, in case you were wondering.



Second, the close proximity of the nerve to the joint capsule predisposes it to injury during arthroscopic capsule release for treatment of adhesive capsulitis. Risk of injury is decreased by placing the incision of the glenohumeral joint capsule at the glenoid insertion with the arm in the abducted and externally rotated position.

We can appreciate the extent of inflammation on other imaging modalities too. On FDG PET/CT, for example, patients with adhesive capsulitis tend to have uptake at the inferior capsule that extends into the adjacent tissues.

References

• Sridharan R, Engle MP, Garg N, Wei W, Amini B. Focal uptake at the rotator interval or inferior capsule of shoulder on ¹⁸F-FDG PET/CT is associated with adhesive capsulitis. Skeletal Radiol. 2017 Apr;46(4):533-538.
• Salem U, Zhang L, Jorgensen JL, Kumar R, Amini B. Adhesive capsulitis mimicking metastasis on 18F-FDG-PET/CT.Clin Nucl Med. 2015 Feb;40(2):e145-7.
• Jerosch J, Filler TJ, Peuker ET. Which joint position puts the axillary nerve at lowest risk when performing arthroscopic capsular release in patients with adhesive capsulitis of the shoulder? Knee Surg Sports Traumatol Arthrosc. 2002 Mar;10(2):126-9.
• E. B. G. D. Santos, P. M. E. Souza (pdf). Teres minor beyond quadrilateral space syndrome: a pictorial review. ECR 2014 conference.

Nerve Root(s)

In season 3, episode 18 of Star Trek: Deep Space Nine Dr. Bashir has to deal with some deep-seated personal issues. One of these is the fact that he graduated second in his medical school class because he mistook a "pre-ganglionic fiber for a post-ganglionic nerve." Spoiler alert: He did it on purpose because he didn't want to deal with the pressure of being first.

Dr. Bashir is not alone. I see this lead to 2 errors every day in our trainees. The clinical implication is zero, because the referring physicians also don't make this distinction (two wrongs do make a right, apparently).

First, take a look at the image below:



Note that there are 2 nerve roots (dorsal and ventral) on each side (left and right). When you say a lumbar disc compresses a nerve root in the central spinal canal, you need to add an "s," because these dorsal and ventral nerve roots travels down together in the cauda equina. Next time you look at an axial T2-WI of the lumbar spine, see if you can see two distinct nerve roots on either side.

Second, note that once we're post-ganglionic, we're dealing with a nerve, not a root. So, if you're talking about a nerve root outside the foramen, you're about as anatomically correct as a Ken doll.


The same goes for the "nerve roots" of the brachial plexus and the famous Randy Travis Drinks Cold Beer mnemonic for the brachial plexus anatomy (sorry, Randy). All is not lost. Just replace Randy Travis with Nikola Tesla.

Reference

• Basic anatomy that everyone ignores.

Vagus Nerve Neurofibroma

Vagus nerve neurofibromas are very rare. They can be located in cervical or mediastinal positions. They are slowly growing and typically asymptomatic.

While the vagus nerve itself can be hard to see, knowledge of the anatomy can be helpful in localization. The vagus nerve travels from the jugular foramen in the carotid sheath between the internal jugular vein (IJ) and internal carotid artery above C4 and between the IJ and common carotid artery (CC) to the root of neck.

The case above shows a T2-hyperintense structure between the IJ and CC at the base of the neck. In this patient with neurofibromatosis, the primary consideration is a vagus nerve neurofibroma.

References

• Gilmer-Hill HS, Kline DG. Neurogenic tumors of the cervical vagus nerve: report of four cases and review of the literature. Neurosurgery. 2000 Jun;46(6):1498-503.
• Kanzaki R, Inoue M, Minami M, Sawabata N, Shintani Y, Nakagiri T, Okumura M. Bilateral mediastinal neurofibroma of the vagus nerves in a patient with neurofibromatosis type 1. Ann Thorac Cardiovasc Surg. 2013;19(4):293-6.
• Matejcik V, Steno J, Haviarova Z, Mravec B. Neurofibroma of the vagus nerve in the cervical portion. Bratisl Lek Listy. 2008;109(10):455-8.
• Sesenna E, Magri AS, Corradi D, Ferri T, Ferri A. Malignant peripheral nerve sheath tumor of the vagus nerve in a teenager with the neurofibromatosis 1 gene mutation: a case report. J Pediatr Surg. 2011 Aug;46(8):e9-12.
• Shintani Y, Ohta M, Hazama K, Minami M, Okumura M, Hirabayashi H, Matsuda H. Bilateral cervicomediastinal neurofibroma originating from the vagal nerve in a patient with von Recklinghausen's disease: report of a case. Surg Today. 2002;32(12):1068-71.

Killian Jamieson Diverticulum

Killian is usually mentioned when discussing the Killian's dehiscence which is the gap in the posterior hypopharynx where the muscle fibers of the cricopharyngeus muscle and inferior constrictor muscle diverge. This site is where Zenker's diverticula occur.

The Killian-Jamieson space is below the cricopharyngeus muscle and lateral to the longitudinal muscle of the esophagus. This muscular gap is the location of the rarer Killian-Jamieson diverticulum. Fluoroscopy will show an outpouching along the anterolateral esophagus inferior to the cricopharyngeus muscle (as opposed to along the posterior esophagus and superior to the cricopharyngeus muscle in the case of a Zenker's diverticulum). 

REFERENCES

Rubesin SE and Levine MS. Killian-Jamieson diverticula. AJR Am J Roentgenol 2001;177:85-9.

SATCHMO

The differential diagnosis of a suprasellar mass can be remembered through the SATCHMO mnemonic.

S - suprasellar/sellar adenoma, sarcoid
A - aneurysm, arachnoid cyst
T - teratoma
C - craniopharyngioma
H - hamartoma (of the tuber cinereum), hypothalamic glioma
M - meningioma
O - optic nerve glioma

The above image is from a patient who presented to the ER several times after multiple motor vehicle accidents. On clinical exam he was found to have visual field defects. NECT demonstrates a hyperattenuating sellar mass. Post operative diagnosis was pituitary macroadenoma.

Lymph Node Stations for Pelvic Tumors

Most pelvic visceral tumors metastasize via lymphatics. Metastases to regional lymph nodes is consider N stage in the TNM classification system while spread to nonregional lymph nodes is considered M stage disease (distant metastases). Since upstaging influences prognosis and clinical management, knowledge of the pelvic nodal anatomy is important in evaluation of cross sectional imaging. 

The following groups of pelvic lymph nodes should be considered:
1. Common iliac lymph nodes: between the aortic bifurcation and the common iliac vessel bifurcation.

• Medial, lateral, and lumbosacral subdivisions
• lumbosacral subdivision refers to lymph nodes in the lumbosacral fossa (triangular region bounded by common iliac vessels medially, psoas muscle laterally, and lower lumbar/upper sacral vertebral bodies posteriorly)

2. External iliac lymph nodes: between the common iliac vessel bifurcation and the inguinal ligament

• Medial and lateral subdivisions
• obturator nodes are considered part of the medial subdivision and gather their name from proximity to the obturator internus muscle

3. Internal iliac lymph nodes: surround the branches of the internal iliac vessels

• Anterior, lateral sacral, and presacral subdivisions
• hypogastric is a term used by some to describe the most cephalic of the internal iliac lymph nodes while others use the term to describe all internal iliac lymph nodes as a group

4. Inguinal lymph nodes: inferior to the inguinal ligament

• Superficial subdivision nodes lie anterior to the inguinal ligament and femoral vessels
• Deep subdivision lymph nodes are enclosed within the femoral sheath

5. Perivisceral nodes: include perirectal, periprostatic, perivesicular nodes


REFERENCES
McMahon CJ, Rofsky NM, Pedrosa I. Lymphatic metastases from pelvic tumors: anatomic classification, characterization, and staging. Radiology 2010;254:31-46.

Anomalies of the Inferior Vena Cava and Their Clinical Significance

1. Left IVC: joins the left renal vein and crosses anterior to the aorta to join the right renal vein

• can be mistaken for paraaortic adenopathy
• report of AAA rupture into the IVC

2. Double IVC: the left IVC ends at the level of the left renal vein which crosses anterior to the aorta to join the confluence of the right IVC/renal vein.

• suspect if patient has recurrent pulmonary embolism after placement of an IVC filter

3. Azygous continuation of the IVC: above the renal veins the IVC passes posterior to the diaphragmatic crus and continues as the azygous vein which joins the superior vena cava in the right paratracheal region. The hepatic segment of the IVC empties directly into the right atrium.

• important to consider in cases of a right paratracheal mass 
• can be mistaken for retrocrural adenopathy

4. Circumaortic left renal vein: two left renal veins are present; the superior renal vein receives the left adrenal vein while the inferior renal vein receives the left gonadal vein.

• significant during planning of nephrectomy

5. Retroaortic left renal vein: a single left renal vein passes posterior to the aorta

• recognition during preoperative planning is important

6. Double IVC with retroaaortic right renal vein and hemiazygous continuation of the IVC: confluence of the right renal vein and right IVC crosses posterior to the aorta to join the left IVC and continue cephlad as the hemiazygous vein. Several collateral pathways for the hemiazygous vein exist in the thorax - hemiazygous crossing posterior to the aorta to join the azygous vein, hemiazygous joining the cardinal vein of the heart via a persistent left SVC, and accessory hemiazygous continuation to the brachocephalic vein

• hemiazygous collateral pathway may be mistaken for a left mediastinal mass
• accessory hemiazygous has been reported to be mistaken for an aortic dissection

7. Circumcaval ureter: always occurring on the right, the proximal ureter courses posterior to the IVC and emerges to the right of the aorta and continues anterior to the right iliac vessels.

• patients may develop partial ureteral obstruction or recurrent urinary tract infections
• treatment is surgical relocation of the ureter anterior to the IVC

8. Absent infrarenal IVC with preservation of the suprarenal segment: external and internal iliac veins converge as lumbar veins which continue cephlad as the paravertebral collateral veins to join the azygous and hemiazygous. The confluence of the renal veins forms a normal suprarenal IVC.

• patients may present with symptoms of lower extremity venous insufficiency or idiopathic deep venous thrombosis
• collateral circulation may mimic a paraspinal mass

REFERENCES

Bass JE, Redwine MD, Kramer LA, et al. Spectrum of congenital anomalies of the inferior vena cava: cross-sectional imaging findings. Radiographics. 2000 May;20:639-52.

Facet Anatomy of the Greater Tuberosity

The superior (anterior) facet of the greater tuberosity is horizontal on coronal oblique MR images and is the site of attachment of the supraspinatus tendon.

The middle facet of the greater tuberosity is obliquely oriented and is the site of attachment of the supraspinatus and infraspinatus tendons. The supraspinatus tendon attaches to the superior half of the middle facet, while the infraspinatus tendon attaches to the entire middle facet, covering a portion of the supraspinatus tendon.

As we move posteriorly, we see both the middle and inferior (posterior) facets. The inferior facet is vertically oriented and is the site of attachment of the teres minor tendon.

References

• Minagawa H, Itoi E, Konno N, Kido T, Sano A, Urayama M, Sato K. Humeral attachment of the supraspinatus and infraspinatus tendons: an anatomic study. Arthroscopy. 1998 Apr;14(3):302-6.

Lateral Recess of the Sphenoid Sinus

Pneumatization of the sphenoid sinus can extend laterally, creating a lateral recess. Pneumatization can then further extend into the pterygoid process, the great wing of the sphenoid bone (as seen abvoe) or both. This can be clinically relevant, as surgical access to lesions in this lateral recess can be challenging.

Coronal images reveal projection of the sphenoid sinus sidewall beyond the foramen rotundum (r). The lateral recess extends into the greater wing of the sphenoid bone above the vidian canal (v) and below the foramen rotundum (r), separating the two. There may be normal side-to-side asymmetry of the vidian-rotundum distance.

The main differential consideration in an opacified sinus is an expansile or erosive process in the sphenoid sinus (e.g., mucoceles or polyps). The most specific evidence of such a process is gross sinus wall erosion and flattening or erosion of the rims of vidian canal or the foramen rotundum.

The patient above has bilateral lateral recesses, with the one on the right extending to the sphenoid wing. The patient also has multiple facial fractures.

References

• Giannetti AV, Guimarães RE, Santiago AP, Perpétuo FO, Machado MA. A tomographic study of the skull base in primary spontaneous cerebrospinal fluid leaks. Neuroradiology. 2011 Jul 8.
• Lewin JS, Curtin HD, Eelkema E, Obuchowski N. Benign expansile lesions of the sphenoid sinus: differentiation from normal asymmetry of the lateral recesses. AJNR Am J Neuroradiol. 1999 Mar;20(3):461-6.
• Tami TA. Surgical management of lesions of the sphenoid lateral recess. Am J Rhinol. 2006 Jul-Aug;20(4):412-6.

Anatomy of the Volar Branch of the Ulnar Nerve at the Wrist

Approximately 5 cm proximal to the wrist, the ulnar nerve divides into its terminal branches: The dorsal and volar branches.

The volar branch crosses the flexor retinaculum on the lateral side of the pisiform and terminates into superficial and a deep branches.

The superficial branch supplies the palmaris brevis and the skin on the ulnar side of the hand.

The deep branch passes between the abductor digiti minimi and flexor digiti minimi brevis muscles, perforates the opponens digiti minimi, and travels deep to the flexor tendons.

The sequence of axial MRIs above shows the terminal branches of the ulnar nerve in the hand and wrist.

References

Gray's anatomy.

Denticulate Ligaments

The denticulate ligaments, also known as dentate ligaments, are pia-arachnoid covered thick collagenous bundles that extend from spinal cord to the dura mater. The 20-21 pairs of denticulate ligaments are located between the dorsal and ventral rootlets and divide the spinal canal into posterior and anterior compartments. They are thought to stabilize the cord within the spinal canal and are used by surgeons as landmarks to localize spinal pathways during cordotomy.

The most cephalad denticulate ligaments attach intracranially. They are located just posterior to the vertebral artery and the ventral rootlets of C1 and anterior to the branches of the posterior spinal artery, spinal accessory nerve and, dorsal rootlets of C1.

The dentate ligaments get denser in the lower thoracic spine and tend to attach to the dura mater closer to the exiting nerve roots compared to those of the cervical and upper thoracic spine.

The most caudal of the denticulate ligaments merge with the pia mater surrounding the filum terminale.

References

• Epstein BS. Cinemyelographic examination of the cervical spinal canal and the craniovertebral junction: the dentate ligaments. Br J Radiol. 1967 Mar;40(471):195-200.
• Kershner DE, Binhammer RT. Lumbar intrathecal ligaments. Clin Anat. 2002 Mar;15(2):82-7.
• Sigmund EE, Suero GA, Hu C, McGorty K, Sodickson DK, Wiggins GC, Helpern JA. High-resolution human cervical spinal cord imaging at 7 T. NMR Biomed. 2011 Dec 20. [Epub ahead of print]
• Tubbs RS, Mortazavi MM, Loukas M, Shoja MM, Cohen-Gadol AA. The intracranial denticulate ligament: anatomical study with neurosurgical significance. J Neurosurg. 2011 Feb;114(2):454-7.
• Tubbs RS, Salter G, Grabb PA, Oakes WJ. The denticulate ligament: anatomy and functional significance. J Neurosurg. 2001 Apr;94(2 Suppl):271-5.

Sphenooccipital Synchondrosis

The sphenooccipital synchondrosis is the cartilagenous space between the basal portion of the sphenoid and occipital bones. Radiographs of the open synchondrosis reveal a lucent band 1 to 3 mm in width across the clivus at the level of the petrous apex. It usually closes by the age of 25. Ossification starts above and proceeds down, and is usually evident on radiographs as superior narrowing around the age of 13.

References

Irwin GL. Roentgen determination of the time of closure of the spheno-occipital synchondrosis. Radiology. 1960 Sep;75:450-3.

Plantar Aponeurosis: Anatomy

The plantar aponeurosis (plantar fascia) is composed of central, medial, and lateral segments. The base is attached to the calcaneus and has fibers continuous with those of the Achilles tendon.

• Medial segment (purple): Arises from the central segment and attaches to the inferior portion of the abductor hallucis muscle.
• Central segment (tan): The thickest component. Its proximal attachment is to the posterior aspect of the medial calcaneal tuberosity (posterior to the origin of the flexor digitorum brevis tendon). Its distal attachments are at the level of the metatarsophalangeal joints, dividing into five pairs of superficial and deep fasicles. The deep branches (blue) insert onto the metatarsophalangeal joints. The superficial branches bifurcate into sagittal septa, which attach onto the plantar plates (red), interosseous ligament, and deep transverse metatarsal ligaments of the 2nd through 5th digits and the plantar plate and sesamoid bones (white) of the great toe.
• Lateral segment (green): Attaches proximally to the lateral aspect of the medial process of the calcaneal tuberosity and is continuous medially with the central segment. Distally, it has a medial band inserts onto the plantar plate of the fourth and sometimes third metatarsophalangeal joints, and a lateral band that attaches to the base of the fifth metatarsal.

References

Moraes do Carmo CC, Fonseca de Almeida Melão LI, Valle de Lemos Weber MF, Trudell D, Resnick D. Anatomical features of plantar aponeurosis: cadaveric study using ultrasonography and magnetic resonance imaging. Skeletal Radiol. 2008 Oct;37(10):929-35.

Posterior Intermalleolar Ligament

The posterior intermalleolar ligament, also known as the marsupial meniscus, is a small ligament in the posterior ankle. It is present in about 60%-80% of the population on autopsy, but can only be seen in about 20% of patients on routine MRI.

The posterior intermalleolar ligament has been erroneously considered as a synonym for the tibial slip of the posterior talofibular ligament. The tibial slip is a band of fibers connecting the posterior talofibular ligament to the medial malleolus, while the posterior intermalleolar ligament converges laterally to a bundle distinct from the posterior talofibular ligament.

Laterally, the fibers of the posterior intermalleolar ligament (red) are attached to the superior margin of the malleolar fossa of the fibula. The medial attachment site is much more variable, and includes the lateral border of the medial malleolar sulcus, the medial border of the medial malleolar sulcus through the septum between flexor digitorum longus and the tibialis posterior tendons, the posterior tibial cortex, the joint membrane covering the posterior process of the talus, and the floor of the flexor hallucis longus tunnel.

On MRI, the normal posterior intermalleolar ligament is a thick string or two or more fine parallel stripes on coronal images. It appears as a linear structure on axial images. On sagittal images, the ligament appears as scattered dots medially and as a thin flat or nodular structure laterally.

The posterior intermalleolar ligament may extend anteriorly, especially along its lateral extent, and give an appearance similar to that of a meniscus. This has been termed the marsupial meniscus due to its similarity to a structure found in marsupials. In marsupials, the talus has a lateral extension that serves as the receptive surface for the fibula, which is a significant weight-bearing component of the joint. A meniscus can be seen in these animals between the fibula and talus.

Entrapment and tearing of the posterior intermalleolar ligament can lead to posterior impingement syndrome, a phenomenon first described in ballet dancers with otherwise structurally normal ankles. The etiology is thought to be repetitive plantar flexion, causing intra-articular extension of the ligament and subsequent fraying and tearing.

MRI findings of posterior impingement syndrome due to posterior intermalleolar ligament pathology include a prominent posterior intermalleolar ligament as indicated by its presence in three different imaging planes and with a caliber comparable to other posterior ankle ligaments seen in the same imaging plane.

References

• Fiorella D, Helms CA, Nunley JA 2nd. The MR imaging features of the posterior intermalleolar ligament in patients with posterior impingement syndrome of the ankle. Skeletal Radiol. 1999 Oct;28(10):573-6.
• Lewis OJ. The joints of the evolving foot. Part I. The ankle joint. J Anat. 1980 May;130(Pt 3):527-43.
• Oh CS, Won HS, Hur MS, Chung IH, Kim S, Suh JS, Sung KS. Anatomic variations and MRI of the intermalleolar ligament. AJR Am J Roentgenol. 2006 Apr;186(4):943-7.
• Rosenberg ZS, Cheung YY, Beltran J, Sheskier S, Leong M, Jahss M. Posterior intermalleolar ligament of the ankle: normal anatomy and MR imaging features. AJR Am J Roentgenol. 1995 Aug;165(2):387-90.

Annulus of Zinn

The annulus of Zinn is a fibrous ring that overlies the optic canal and the medial aspect of the superior orbital fissure and is continuous with the dura of the middle cranial fossa. It is divided into the superior Lockwood tendon and the inferior tendon of Zinn.

Six of the seven extraocular muscles arise from the annulus of Zinn: The four rectus muscles, the levator palpebrae superioris muscle, and the superior oblique muscle. The inferior oblique muscle arises from the medial orbital floor lateral to the lacrimal sac.

Cranial nerves II, III, nasocilliary branch of V1, and VI enter through the annulus of Zinn, while Cranial nerves IV and the frontal and lacrimal branches of the ophthalmic division of the trigeminal nerve (V1) enter the orbit through the superior orbital fissure lateral to the annulus of Zinn.

The ophthalmic artery also passes through the annulus of Zinn, while the superior ophthalmic vein enters the orbit through the superior orbital fissure lateral to the annulus of Zinn. The diagram, adapted from Petruzzelli and Hampson, shows the right orbit. 2=cranial nerve II; 3i=inferior division of cranial nerve III; 3s=superior division of cranial nerve III; 4=cranial nerve IV; 6=cranial nerve VI.

References

• Aviv RI, Casselman J. Orbital imaging: Part 1. Normal anatomy. Clin Radiol. 2005 Mar;60(3):279-87
• Petruzzelli GJ and Hampson CM. Orbit Anatomy. eMedicine. Mar 11, 2008.

Ovarian Artery Variants

The ovarian arteries most commonly (80%-90% of cases) arise anteromedially from the abdominal aorta a few centimeters inferior to the origin of the renal arteries. They may be difficult to visualize on angiography due to their small caliber (< 1 mm). If they are seen, they demonstrate a characteristic corkscrew appearance. The ovarian arteries may also arise from the renal, lumbar, adrenal, or iliac arteries.

In 40% of cases, the ovaries are supplied solely by the ovarian arteries. In about 55% of cases, both the uterine and ovarian arteries supply the ovaries, while in about 5% of cases, the uterine arteries alone supply the ovaries.

The last variant may be due congenital absence of the ovarian artery, occlusive lesions at the level of the ovarian artery or the aorta, or ovarian abnormalities (e.g., tumor or inflammatory conditions causing neovascularization). If such a case is identified on angiography, a coexistent ovarian abnormality must be excluded.

Another source of variability important in uterine fibroid embolization (UFE) is the different anastomotic connections between the uterine and ovarian arteries, which may be seen in up to 30% of cases.

• Type I: There is flow from the ovarian artery to the uterus through anastomoses with the tubal branch of the uterine artery. Following UFE, the ovarian supply is not likely to be a source of procedural failure.
  • Type Ia: Flow in the tubal artery is toward the uterus, without evidence of retrograde reflux to the ovary.
  • Type Ib: Flow in the tubal artery is toward the uterus, but there is evidence of retrograde reflux to the ovary. Injection of embolic particles into the uterine artery may cause reflux into the tubo-ovarian segment and may cause embolization of the ovary.
• Type II: There is a direct blood supply to a fibroid from the ovarian artery without prior connection to the uterine artery. Following UFE, the fibroid may continue to be supplied, and the ovarian artery can be a cause of procedural failure.
• Type III: The dominant blood supply to the ovary is from the uterine artery (see also above). This is important in UFE, as there is a high likelihood of ovarian artery embolization.

References

• Pelage JP, Cazejust J, Pluot E, Le Dref O, Laurent A, Spies JB, Chagnon S, Lacombe P. Uterine fibroid vascularization and clinical relevance to uterine fibroid embolization. Radiographics. 2005 Oct;25 Suppl 1:S99-117.
• Razavi MK, Wolanske KA, Hwang GL, Sze DY, Kee ST, Dake MD. Angiographic classification of ovarian artery-to-uterine artery anastomoses: initial observations in uterine fibroid embolization. Radiology. 2002 Sep;224(3):707-12.

Rhomboid Fossa of the Clavicle

The rhomboid fossa is a normal concave lucent irregularity that may be seen along the inferomedial aspect of the clavicle. It is the insertion site of the costoclavicular ligament. The rhomboid fossa may be mistaken for an osteolytic lesion or apical pneumothorax.

References

Kumar R, Madewell JE, Swischuk LE, Lindell MM, David R. The clavicle: normal and abnormal. Radiographics. 1989 Jul;9(4):677-706.