Pseudoachalasia of the cardia-Ba Swallow and CT

66 year old male patient presents with history of dysphagia for solids and liquids since 3 months and chest radiograph was normal. Barium esophagogram showing long segment smooth narrowing in the distal esophagus with significant dilatation and hold up of contrast in the proximal esophagus. On noticing carefully there is mild irregularities in the GE junction and cardiac end of stomach. We kept the possibility of achalasia and pseudoachalasia. Advised further workup of CT scan and endoscopy.

Contrast enhanced CT scan with on table oral contrast showing concenteric wall thicekning (arrow) obliterating the lumen in the distal esophagus involving GE junction and having less than 90 degrees of contact with the descending thoracic aorta and abutting left atrium. Endoscopic biopsy revealed adenocarcinoma. These findings are consistent with pseudoachalasia.

Achalasia cardia is due to loss of myenteric ganglion cells in the gastroesophageal junction and the etiology is idiopathic. But a similar clinical picture can be produced by other diseases, a condition termed as secondary or pseudoachalasia. A very high index of suspicion is required for the diagnosis of this condition because this is most commonly produced by a malignancy involving the gastroesophageal junction which is likely to be missed. In true or primary achalasia, there is loss of myenteric ganglion cells with loss of peristalsis in esophageal body and failure of lower esophageal sphincter to relax when swallowing. Barium swallow shows a typical bird's beak appearance.

The causes for pseudoachalasia include primary malignancy of esophagus or gastroesophageal junction, 53.9%, secondary malignancies such as metastasis from lung or breast, 14.9%, benign disorders like mesenchymal tumors, secondary amyloidosis and peripheral neuropathy, 12.6%, and as a postoperative complication following antireflux surgery, 11.9%. Other rare causes are neurological disorders like meningomyelocele, brain metastasis, infiltration by lymphoma and paraneoplastic syndromes associated with small cell carcinoma lung, bronchial carcinoids and pleural mesothelioma.

It is very important to differentiate pseudoachalasia from true achalasia. The patients with pseudoachalasia tend to be older in age ( more than 60 years), have shorter duration of dysphagia (less than 6 months) and have more substantial weight loss. Barium swallow may reveal a nodular of shouldered segment of distal esophageal narrowing. The length of the narrowed esophageal segment was found to be longer than 3.5 cm in 80% of the patients with pseudoachalsia which is the most important feature in radiological differentiation. A CT scan may show asymmetric thickening of the esophageal wall or cardia, mediastinal lymphadenopathy or may identify primary malignancy in secondary achalasia.

Methylmalonic acidaemia (MMA)

3 year old female child came with developmental delay, lethargy, seizures and hypoglycemia, MRI brain T2 weighted image at the level of basal ganglia showing bilateral symmetrical hyperintensities in globi pallidi.

MMA encompasses a heterogeneous group of disorders characterized by accumulation of methylmalonic acid and its by-products in biological fluids. These disorders are due to a deficiency of the adenosylcobalamin-dependent enzyme methylmalonyl-CoA mutase (apoenzyme deficiency), a defect in intracellular cobalamin metabolism (coenzyme deficiency), transcobalamin II deficiency, intrinsic factor deficiency, or dietary cobalamin deficiency, which is found in vegetarians. The incidence, as derived form a neonatal screening program, is one in 48,000 live births (6). The actual occurrence, however, is estimated to be one in 25,000 live births.

CT and MR imaging of the brain typically reveal atrophy, delay in myelination, and abnormalities in the basal ganglia, predominantly in the globi pallidi. The globi pallidi are particularly sensitive to mitochondrial dysfunction, and are thus prime targets for injury. MR Spectroscopy may show elevated lactate levels either in CSF or in brain parenchyma i.e regions of infarcts. Differential diagnosis for bilateral globi pallidi lesions are HIE (hypoxic ischemic encephalopathy), kernicterus, mitochondrial encephalopathy etc.

MOYAMOYA DISEASE

Two year old male boy presented with recurrent episodes of transient ischemic attacks since the age of 6 months following which he has delayed milestones. The boy also has seizures since one year. He was referred to MRI brain for further evaluation.

Figure a) T1weighted image at the level of basal ganglia show multiple tiny low intensity rounded areas seen in bilateral basal ganglia (arrows) which appear hyperintense on T2 weighted images suggestive of collateral vessels. c) Fluid attenuation inversion recovery (FLAIR) sequence showing atrophy involving bilateral frontal and left parietal cortical areas with chronic ischemic changes. d) Volume rendered 3D time of flight frontal projection cerebral angiography showing significant stenosis in the supraclinoid internal carotid arteries on both the sides with absent flow in the anterior and middle cerebral arteries and multiple collaterals in bilateral basal ganglia appearing as “puff of smoke” (moyamoya). Cause is unknown in this boy.

Discussion:

The term ‘moyamoya’ means ‘wavering puff of smoke’, described by Takaku, Suzuki and others in Japan in the sixties1. Moyamoya disease is a cerebrovascular disease that features narrowing or stenosis, starting at the distal internal carotid and proximal portions of the anterior and middle cerebral arteries of unknown etiology. Moyamoya syndrome is a phenomenon caused by an oligemic state similar in presentation but caused by various disease entities. Some of the conditions associated with Moyamoya syndrome are chromosomal disorders (Neurofibromatosis, Down’s syndrome), hemolytic anemias, infectious diseases (leptospirosis, tuberculous meningitis), neoplasms (Craniopharyngioma, Wilms tumor), drug abuse (phenobarbitol) and others. Etiology of Moyamoya disease is still unknown. There have been recent reports of increased familial incidence of the disease with markers on chromosome 6 and 17, located at 3p24.2-26 and a possible linkage of the marker D6S441 to the disease on chromosome 6. Moyamoya is commonly seen during first decade of life. Frequently the children present with transient ischemic attacks or ischemic strokes. Cerebral ischemia may also present as reversible ischemic neurological deficit, sensory attacks or acute infantile hemiplegia. Headaches, involuntary choreiform movements, seizures and other motor disturbances have been described2.

Majority of children (50-60%) show atrophy of anterior brain more than posterior brain on CT scan, where as adults show hemorrhage especially in intraventricular region. Contrast enhanced CT shows enhancing dots in basal ganglia and ‘net like’ vessels at the base of brain. MRI and MR angiography are diagnostic imaging modality of choice. MRI show multiple dot-like flow voids in basal ganglia on T1 weighted image (WI). Flow voids in the multiple collateral vessels in the cisterns appearing as ‘net like’ cisternal filling defects, associated with hyperintense small vessel cortical and white matter infarcts are seen on T2 WI. Slow flowing engorged pial vessels with thickened arachnoid membranes appear as bright sulci called leptomeningeal “ivy sign”. MR angiography show narrowed distal ICA and proximal Circle of Willis vessels with multiple lenticulostriate and thalamoperforator collaterals giving appearance of a “puff of smoke”. MR spectroscopy will show lactate peak in acutely infracted tissue. Treatment is mainly Encephalo-duro-arterio-synangiosis (EDAS) which is a method of indirect bypass2.

Teaching point:

Moyamoya disease or syndrome should be suspected in a child with recurrent ischemic attacks. MRI with MR angiography is the investigation of choice in this condition. MRI shows multiple dot-like flow voids in basal ganglia on T1 WI and flow voids in the multiple collateral vessels in the cisterns appear as ‘net like’ cisternal filing defects on T2WI. MR angiography show narrowed distal ICA and proximal Circle of Willis vessels with multiple lenticulostriate and thalamoperforator collaterals giving appearance of a “puff of smoke” which is typical appearance of moyamoya.

References:

1. Hoffman HJ. Moyamoya disease and syndrome. Clin Neurol Neurosurg1997; 99 Suppl 2 : S39-44
2. Gosalakkal JA. Moyamoya disease: a review. Neurol India. 2002 Mar;50(1):6-10.
3. Fujisawa I, Asato R, Nishimura K, Togashi K, Itoh K, Noma S, et al. Moyamoya disease: MR imaging. Radiology. 1987 Jul;164(1):103-5.

Putty kidney

43 year old female came for USG evaluation of abdomen to rule out metastasis from carcinoma breast. This USG showing calcified mass in whole of the left kidney witch is maintaining the renal contour with posterior acoustic shadow suggestive of putty kidney.

Putty kidney is an end stage of infection with tuberculosis in the genitourinary tract, calcification may entirely outline a nonfunctional kidney.The radiologic appearance of this condition, completely calcified kidney which is associated with autonephrectomy, has been described as the putty kidney. It is very common to see the radiographic and CT appearance of putty kidney but unusual to see the USG features of putty kidney.

MEDIASTINAL NEUROBLASTOMA

One year old female baby came with history of persistent cough, difficulty in breathing and stridor. Baby also had weight loss and sometimes mild fever. Routine hematological investigations were normal. Chest radiograph and contrast enhanced CT scan showed below mentioned findings

Figure 1 a) Radiograph frontal view showing homogenous opacity lesion in the right upper and mid zone with broad base towards mediastinum. The lesion is causing shift of mediastinum and trachea to the contralateral side and compressing the trachea just above the carina (arrow head). The lesion is extending above the clavicle (cervico-thoracic sign) and erosion of posterior end of third and fourth ribs (Long arrow). C) Contrast enhanced CT scan axial section mediastinal window showing heterogeneously enhancing mass lesion in the right posterior mediastinum extending to middle mediastinum causing compression of the trachea. The lesion is showing multiple small foci of calcification (black arrows in fig c).

Discussion:

Primary mediastinal neuroblastoma accounts for 14% of all neuroblastomas. Common location is posterior mediastinum, where they arise from paravertebral sympathetic chain. Patient commonly present with chest pain, cough and respiratory distress due to airway obstruction. Chest radiograph is the initial radiological investigation to be done in such patients. It demonstrates homogenous opacity mass in the mediastinum. If the tumor is large, there may be extrinsic compression and displacement of trachea and main bronchus with mediastinal shift (fig a-c). Rib erosion and asymmetrical widening of inercostal spaces may be seen on radiograph. Intraspinal extension may be seen as loss of vertebral height with widening of neural foramina on lateral radiograph. Approximately 50% of the lesions show calcification on radiograph.

CT scan is usually done to confirm the presence of lesion, and it also helps to define the location and extent of lesion, adjacent organ involvement, or vascular involvement. CT demonstrates calcification in up to 90%. The lesion characterization has become better with the advent of multiplanar image reconstructions in MDCT. However MR imaging is the investigation of choice for better characterization and demonstration of full extent of mass, extradural intraspinal extension and chest wall invasion. The advantages of MR over CT are its direct multiplanar imaging and better contrast resolution, which can allow differentiation of vascular from non vascular lesions without the aid of intravenous contrast agent. MR is very often used to evaluate tumor involving spine and spinal canal.

Teaching point:

Radiograph is the initial investigation to be done in the mediastinal masses and one should be able to identify the lesion and arrive at differential diagnosis. CT scan and MRI are done to confirm the lesion, location, extent, adjacent organ involvement or vascular involvement and intraspinal extension.

Congenital CMV infection

CT scan of 5 month old male showing paucity of white matter, gross hydrocephalus with periventricular calcification and patchygyria suggestive of congenital TORCH infection most likely CMV infection.

Cytomegalovirus infection may be acquired prenatally or perinatally. Signs at birth, if present, are intrauterine growth restriction, prematurity, microcephaly, jaundice, petechiae, hepatosplenomegaly, periventricular calcifications, chorioretinitis, and pneumonitis. Later in infancy, signs are pneumonia, hepatosplenomegaly, hepatitis, thrombocytopenia, and atypical lymphocytosis. Diagnosis is by virus isolation or serology. Treatment is supportive. Parenteral ganciclovir can prevent hearing deterioration, but its use remains controversial.

Differential diagnosis: TORCH infection, Congenital lymphocytic choriomeningitis, Pseudo-TORCH syndrome, Tuberous sclerosis.

Pseudo-torch syndrome: A rare genetic syndrome characterized by a small head, eye disease and brain abnormalities.

Medullary nephrocalcinosis

Ultrasonography of both kidneys in 9 year old female showing multiple areas of increased echogenicity involving all of the medullary pyramids consistent with nephrocalcinosis. The renal cortex is normal in echogenicity. There is no evidence of hydronephrosis.

Medullary nephrocalcinosis refers to calcification in the medullary pyramids rather than the renal collecting system. It is caused by a number of processes, but the three most common are : hyper-parathyroidism medullary , renal tubular acidosis and sponge kidney (tubular ectasia). Medullary nephrocalcinosis is usually associated with hypercalcuria and often with hypercalcemia. Primary hyperparathyroidism and distal renal tubular acidosis account for over 60% of these cases. The remaining 40% of cases are due to a variety of other causes of hypercalciuria, including milk-alkali syndrome, Cushing's syndrome, bony metastases, hyperthyroidism, hypothyroidism, sarcoidosis, furosemide therapy, and in this case, vitamin D therapy.

Ultrasonography is more sensitive than conventional radiography and CT and sonography is unusually sensitive in detecting this condition, and the sonographic changes predate any visible calcification and are generally more dramatic than the abnormalitie seen on CT. Nephrocalcinosis may affect some or ail of the pyramids. The deposits of calcium phosphate and calcium oxalate in the interstitium of the renal pyramids reverse the sonographic appearance of the normal kidneys. The pyramids are normally hypoechoic relative to the cortex. In its early stages it causes increased medullary echogenicity at the periphery of the pyramids and eventually involves the entire pyramids. With progressive calcification, shadowing begins. A regular arrangement of hyperechoic pyramids are seen which may shadow if large calcified foci are present, but not if the foci are numerous and tiny, as they are smaller than the beam width. Less frequently, calcification is seen in the renal cortex.

Cardiac hydatid cyst

CT scan of 58 year old male patient showing large well defined well capsulated hypodense lesion seen in the myocardium of the left ventricle with multiple daughter cysts within suggestive of hydatid cyst.

• Hydatid disease is a parasitic infection caused by larvae of Echinococcus granulosus, which is still endemic in many sheepraising countries.
• Hydatid cysts can be located in various tissues, although they are most common in the liver (50–70% of cases) and the lung (20–30% of cases) in humans.
• Cardiac involvement in hydatid disease is uncommon, constituting only 0.5–2% of all cases of hydatidosis.
• Heart involvement - LV – 60%, RV – 10%, pericardium – 7%, pulm Artery – 6%, left atrial appendage – 6%, and interventricular septum is rare – 4%.
• Cardiac involvement occurs by invasion of the myocardium - Through coronary circulation or pulmonary vein from rupture of pulm cysts in to vein.

• Signs and Symptoms •No symptoms due to its latency and slow growing nature unless it is situated in critical site. •Signs and symptoms are extremely variable and directly related to location and size of the cysts. •Precordial pain is the most common symptom and is most often vague and does not resemble angina pectoris. •Sudden rupture of intracardiac cysts is a frightful complication and can cause acute pericarditis or tamponade, acute pulmonary hypertension by embolization of several scolices, systemic arterial embolization, and severe anaphylactic shock can be life thretening.

• Imaging - Echocardiography, CT, and MRI can show the cystic nature of the mass and its relation to the cardiac chambers •CT best shows wall calcification. •MRI depicts the exact anatomic location and nature of the internal and external structures and is the technique used for posttreatment follow-up.
• The appearance of a hydatid cyst on MRI is usually a characteristic oval lesion that is hypointense on T1-weighted images and hyperintense on T2-weighted images. •A typical finding on T2-weighted images is a hypointense peripheral ring, which represents the pericyst (a dense fibrous capsule from the reactive host tissue). •A variety of tumors in the heart and a congenital pericardial cyst must be considered in the differential diagnosis; however, the multivesicular nature of the cystic mass and membrane detachment indicate the true diagnosis.
• The cysts may be single or multiple, uni or multiloculated, and thin or thick walled. •More specific signs are •Cyst wall calcification. •Presence of daughter cysts and Membrane detachment.
• •Surgery remains the treatment of choice in the management of hydatid disease. •Although antihelminthic drugs have been used in the preoperative and postoperative periods since 1977, extirpation of the lesion under cardiopulmonary bypass is recommended.
• To conclude CT and MRI are helpful for localizing and defining the morphologic features of hydatid cysts. •Specific signs include calcification of the cyst wall, presence of daughter cysts, and membrane detachment. •CT best shows wall calcification, whereas MRI depicts the exact anatomic location and nature of the internal and external structures.

Antenatal diagnosis Chiary II malformation - Fetal MRI

Gravida two female with previous history of abortion came for fetal MRI to ruleout congenital malformation showing lumbosacral myelomeningocele (arrow in first and third image), tonsillar herniation and corpus callosum dysgenesis (arrow in second image). features suggestive of Chiary 2 malformation.

The Austrian pathologist Hans Chiari in the late 1800s described seemingly related anomalies of the hindbrain, the so called Chiari malformations I, II and III. Later, other investigators added a fourth (Chiari IV) malformation.

Types include

Type I - Is generally asymptomatic during childhood, but often manifests with headaches and cerebellar symptoms. Herniation of cerebellar tonsils

Type II - Usually associated with myelomeningocele leading to partial or complete paralysis below the spinal defect. Abnormal development of the cerebellar vermis andmedulla oblongata occur, and they both descend into the foramen magnum. Hydrocephalus is frequently present.

Type III - Type II associated with with an encephalocele.

Type IV - Lack of cerebellar development.

The Chiari II malformation is a complex congenital malformation of the brain, nearly always associated withmyelomeningocele. This condition includes downward displacement of the medulla, fourth ventricle, and cerebellum into the cervical spinal canal, as well as elongation of the pons and fourth ventricle, probably due to a relatively small posterior fossa.

MRI Brain in Carbon monoxide poisoning

18 year old boy came with dizziness, head ache, nausea and loss of conciousness. Gives history of overnight sleeping in the room with burning charcoal heater. MRI FLAIR and T2 (a&b) image showing bilateral symmetrical hyperintensities in globus pallidi. (c&d) diffusion weighted images showing no restriction. features consistent with carbon monoxide poisoning.

In carbon monoxide poisoning, the gas crosses the alveolar capillary membrane and binds strongly with heme containing compounds. The toxicity is due to hypoxia and carbon monoxide mediated damage at the cellular level. Globus pallidus and pars reticulata of substantia nigra are the regions of the highest iron content in the brain. Carbon monoxide directly binds to heme iron in these two regions.

MRI in acute carbon monoxide poisoning, the abnormalities are detected as T2 hyperintensities. Lesions are in the basal ganglia involving the globus pallidus, putaman, caudate nucleus with other areas such as periventricular white matter, subcortical white matter, cerebral cortex, medial temporal lobe (hippocampus) and cerebellum. Diffusion Weighted Imaging(DWI) and MR Sprectroscopy are also useful. Diffusion weighted imaging shows diffuse hyperintensity in periventricular white matter and semiovale, splenium of corpus callosum, internal capsules, and brainstem, with moderately decreased apparent duffusion co-efficient (ADC) values. In the globus pallidus, the ADC values are rather increased, with low signal intensities on DWI as seen in this case. The MRS (MR Spectroscopy) demonstrates decreases n-acetyl aspartase in bilateral basal ganglia.

Focal Nodular Hyperplasia of Liver - CT and MRI

MRI of 30 year old female T1 weighted image showing well defined slightly hypointense lesion with central hypointense scar which is showing slightly hyperintense on T2 WI. In venous phase the lesion is showing homogeneous contrast enhancement (arrow). In delayed phase image there is enhancement of scar.

CT of another 28 year old female showing well defined showing arterial enhanging lesion in the left lobe of liver with central non enhancing scar. On venous phase image the lesion shows homogeneous contrast enhancement. In delayed phase image there is enhancement of scar.
Discussion:

FNH is considered a non-neoplastic, hyperplastic response to a congenital vascular malformation. Histologically, FNH is not a tumor and consists of benign-appearing hepatocytes occurring in a liver that is otherwise normal (i.e. no cirrhosis).
On CT scan the FNH are hypervascular lesions with homogeneous enhancement in arterial phase and hypodense central scars in arterial and venous phase, which enhance in the equilibrium phase. This is characteristic of FNH.
On MR typical FNH is slightly hypointense on T1WI and slightly hyperintense on T2WI. The scar is somewhat hyperintense on T2. The enhancement is as we expect with 'capillary blush' with a scar that enhances late in the equilibrium phase. We need to differentiate fibrolammellar carcinoma (FLC) of liver from FNH as the imaging findings are almost similar except for few differentiating points. The central scar is hyperintense on T2 in FNH where as it is Hypo in FLC. Scar enhances in delayed phase of contrast study in FNH where as it will not enhances in FLC. May see calcification in FLC and not in FNH.

Osteosarcoma of Sternum

CT scan and MRI of 40 year old male came with swelling and pain in the sternum since 3 months shows large destructive soft tissue mass lesion in the body of sternum having osteoid matrix. The lesion is extending anteriorly in the subcutanesous region, psoteriorly in to mediastinum abutting large vessels. We can better appreciate the sternal destruction in SSD image. MR T2 weighted image shows hyperintense signal throughout the lesion. Histopathology proved to be osteosarcoma.

The primary sternal tumors are quite rare. The most commonly occurring malignant tumor in sternum is chondrosarcoma and occurrence of osteosarcoma in sternum is extremely rare. The most common tumors of sternum are the metastases of lung, renal or thyroidal malignancies. CT may show lytic, mixed or sclerotic pattern and it is observed as an expansile mass lesion with irregular borders, and the lesion invades bone marrow by destroying the cortex. MRI clearly demonstrates the extent of the lesion and characterization of the lesion.

Occular Metallic Foreign body

17 year old male CT coronal, axial and coronal bone window showing metallinc foreign body in the right globe adherent to lateral wall.
Metallic foreign body in another patient in right orbit on radiograph (arrow). CT scan axial section of the same patient showing foreign body just posterior to the limbus which is extra occular.

Intraocular foreign bodies (IOFBs) are rather variable in presentation, outcome, and prognosis. With increased awareness and advanced surgical techniques, the outcome and the prognosis for these potentially devastating injuries have substantially improved.

CT scans are the imaging study of choice for IOFB localization. A helical CT scan is the most efficient method to establish a diagnosis. Helical CT scans have a very high identification rate. With conventional CT scans, cuts of 0.5 mm are advised. With the advent of MDCT the role of radiologist has become easier in identification and diagnosis of occular foreign body. Plain x-ray is useful if a metallic IOFB is present and a CT scan is unavailable. MRI is generally not recommended for metallic IOFBs. Ultrasound is a useful tool in localizing IOFBs, and its careful use is possible even if the globe is still open; alternatively, intraoperative use after wound closure can be attempted. The ultrasound biomicroscope may help with IOFBs in the anterior segment.

Pheochromocytoma

MRI abdomen of 14 year old male patient came with uncontrolled hypertension with raised urinary catecholamines showing well defined focal soft tissue intensity mass in the left supra renal gland having intensely hyperintense on T2 W image and hypointense on T1W image. Features are consistent with pheochromocytoma.

Pheochromocytomas are rare but treacherous catecholamine-producing tumors, which if missed or not properly treated, will almost invariably prove fatal. Prompt diagnosis is, therefore, essential for effective treatment, usually by surgical resection. The manifestations are diverse and the tumor can mimic a variety of conditions, often resulting in either erroneous diagnoses or a delayed diagnosis. Imaging is very essential for accurate diagnosis.

Pheochromocytomas are extra adrenal (10%), multicentric (10%), bilateral (5%), and malignant (10%)..Size is variable from 1-20 cm.The treatment is surgical excision of tumor, which is curative in all cases. The initial imaging findings in benign and malignant pheochromocytomas are nearly identical. Only the presence of metastasis can clearly define a lesion as malignant. On CT it appears as round or oval discrete mass with homogenous density. Similar findings have been noted in the present case. Central necrosis, calcification and cystic changes may be present in minority of cases. These vascular lesions enhance uniformly after administration of contrast material. MR is also excellent for evaluating intraadrenal pheochromocytoma.On T1, mass has intensity similar to or slightly less than solid organs. OnT2 lesion is hyper intense as result of their long T2 time. Sometimes adrenal metastases also present overlapping imaging findings. Combination of MIBG,CT and MRI scanning is definitive in the diagnosis of pheochromocytoma.

Focal Pyelonephritis

40 year old male patient came to emergency with history of right lumbar pain and fever, USG Doppler of right kidney shows focal hypoechoic area in upper pole with small anechoic area within. CT scan of the same patient showwed focal hypoenhancing lesion in upper pole of right kidney with small non enhancing area within. These features are suggestive of focal pyelonephritis with evolution of abscess.

Acute focal pyelonephritis (AFP) is a variant of pyelonephritis in which single or multiple discrete areas show changes of inflammation. The sonographic appearances of AFP are varied and can be echogenic, echopoor or of mixed echogenicity, but are typically described as being echopoor. CT typically shows focal hypoenhancing areas. Imaging is done mainly to identify the complications like intra renal and peri renal abscess.